Input output checking (#9680)

# Description

This PR tights input/output type-checking a bit more. There are a lot of
commands that don't have correct input/output types, so part of the
effort is updating them.

This PR now contains updates to commands that had wrong input/output
signatures. It doesn't add examples for these new signatures, but that
can be follow-up work.

# User-Facing Changes

BREAKING CHANGE BREAKING CHANGE

This work enforces many more checks on pipeline type correctness than
previous nushell versions. This strictness may uncover incompatibilities
in existing scripts or shortcomings in the type information for internal
commands.

# Tests + Formatting
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crates/nu-cmd-extra/src/extra/bits/and.rs

@@ -15,7 +15,13 @@ impl Command for BitsAnd {
 
     fn signature(&self) -> Signature {
         Signature::build("bits and")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required(
                 "target",

crates/nu-cmd-extra/src/extra/bits/not.rs

@@ -16,7 +16,13 @@ impl Command for BitsNot {
 
     fn signature(&self) -> Signature {
         Signature::build("bits not")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .switch(
                 "signed",

crates/nu-cmd-extra/src/extra/bits/or.rs

@@ -15,7 +15,13 @@ impl Command for BitsOr {
 
     fn signature(&self) -> Signature {
         Signature::build("bits or")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required(
                 "target",

crates/nu-cmd-extra/src/extra/bits/rotate_left.rs

@@ -18,7 +18,13 @@ impl Command for BitsRol {
 
     fn signature(&self) -> Signature {
         Signature::build("bits rol")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required("bits", SyntaxShape::Int, "number of bits to rotate left")
             .switch(

crates/nu-cmd-extra/src/extra/bits/rotate_right.rs

@@ -18,7 +18,13 @@ impl Command for BitsRor {
 
     fn signature(&self) -> Signature {
         Signature::build("bits ror")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required("bits", SyntaxShape::Int, "number of bits to rotate right")
             .switch(

crates/nu-cmd-extra/src/extra/bits/shift_left.rs

@@ -18,7 +18,13 @@ impl Command for BitsShl {
 
     fn signature(&self) -> Signature {
         Signature::build("bits shl")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required("bits", SyntaxShape::Int, "number of bits to shift left")
             .switch(

crates/nu-cmd-extra/src/extra/bits/shift_right.rs

@@ -18,7 +18,13 @@ impl Command for BitsShr {
 
     fn signature(&self) -> Signature {
         Signature::build("bits shr")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required("bits", SyntaxShape::Int, "number of bits to shift right")
             .switch(

crates/nu-cmd-extra/src/extra/bits/xor.rs

@@ -15,7 +15,13 @@ impl Command for BitsXor {
 
     fn signature(&self) -> Signature {
         Signature::build("bits xor")
-            .input_output_types(vec![(Type::Int, Type::Int)])
+            .input_output_types(vec![
+                (Type::Int, Type::Int),
+                (
+                    Type::List(Box::new(Type::Int)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .required(
                 "target",

crates/nu-cmd-extra/src/extra/bytes/length.rs

@@ -16,7 +16,13 @@ impl Command for BytesLen {
 
     fn signature(&self) -> Signature {
         Signature::build("bytes length")
-            .input_output_types(vec![(Type::Binary, Type::Int)])
+            .input_output_types(vec![
+                (Type::Binary, Type::Int),
+                (
+                    Type::List(Box::new(Type::Binary)),
+                    Type::List(Box::new(Type::Int)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-cmd-extra/src/extra/bytes/remove.rs

@@ -30,7 +30,10 @@ impl Command for BytesRemove {
 
     fn signature(&self) -> Signature {
         Signature::build("bytes remove")
-            .input_output_types(vec![(Type::Binary, Type::Binary)])
+            .input_output_types(vec![
+                (Type::Binary, Type::Binary),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .required("pattern", SyntaxShape::Binary, "the pattern to find")
             .rest(
                 "rest",

crates/nu-cmd-extra/src/extra/bytes/replace.rs

@@ -30,7 +30,10 @@ impl Command for BytesReplace {
 
     fn signature(&self) -> Signature {
         Signature::build("bytes replace")
-            .input_output_types(vec![(Type::Binary, Type::Binary)])
+            .input_output_types(vec![
+                (Type::Binary, Type::Binary),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .required("find", SyntaxShape::Binary, "the pattern to find")
             .required("replace", SyntaxShape::Binary, "the replacement pattern")
             .rest(

crates/nu-cmd-extra/src/extra/math/cos.rs

@@ -13,7 +13,13 @@ impl Command for SubCommand {
     fn signature(&self) -> Signature {
         Signature::build("math cos")
             .switch("degrees", "Use degrees instead of radians", Some('d'))
-            .input_output_types(vec![(Type::Number, Type::Float)])
+            .input_output_types(vec![
+                (Type::Number, Type::Float),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Float)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .category(Category::Math)
     }

crates/nu-cmd-extra/src/extra/math/sin.rs

@@ -13,7 +13,13 @@ impl Command for SubCommand {
     fn signature(&self) -> Signature {
         Signature::build("math sin")
             .switch("degrees", "Use degrees instead of radians", Some('d'))
-            .input_output_types(vec![(Type::Number, Type::Float)])
+            .input_output_types(vec![
+                (Type::Number, Type::Float),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Float)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .category(Category::Math)
     }

crates/nu-cmd-extra/src/extra/math/tan.rs

@@ -13,7 +13,13 @@ impl Command for SubCommand {
     fn signature(&self) -> Signature {
         Signature::build("math tan")
             .switch("degrees", "Use degrees instead of radians", Some('d'))
-            .input_output_types(vec![(Type::Number, Type::Float)])
+            .input_output_types(vec![
+                (Type::Number, Type::Float),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Float)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .category(Category::Math)
     }

crates/nu-cmd-extra/tests/commands/bytes/starts_with.rs

@@ -21,7 +21,7 @@ fn basic_string_fails() {
         "#
     );
 
-    assert!(actual.err.contains("Input type not supported"));
+    assert!(actual.err.contains("command doesn't support"));
     assert_eq!(actual.out, "");
 }
 

crates/nu-cmd-lang/src/core_commands/collect.rs

@@ -16,7 +16,7 @@ impl Command for Collect {
 
     fn signature(&self) -> Signature {
         Signature::build("collect")
-            .input_output_types(vec![(Type::List(Box::new(Type::Any)), Type::Any)])
+            .input_output_types(vec![(Type::Any, Type::Any)])
             .required(
                 "closure",
                 SyntaxShape::Closure(Some(vec![SyntaxShape::Any])),

crates/nu-command/src/conversions/into/decimal.rs

@@ -17,15 +17,21 @@ impl Command for SubCommand {
     fn signature(&self) -> Signature {
         Signature::build("into decimal")
             .input_output_types(vec![
+                (Type::Int, Type::Number),
                 (Type::String, Type::Number),
                 (Type::Bool, Type::Number),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Number)),
+                ),
             ])
             .rest(
                 "rest",
                 SyntaxShape::CellPath,
                 "for a data structure input, convert data at the given cell paths",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Conversions)
     }
 

crates/nu-command/src/conversions/into/int.rs

@@ -36,10 +36,17 @@ impl Command for SubCommand {
                 (Type::Bool, Type::Int),
                 // Unix timestamp in nanoseconds
                 (Type::Date, Type::Int),
+                (Type::Duration, Type::Int),
                 // TODO: Users should do this by dividing a Filesize by a Filesize explicitly
                 (Type::Filesize, Type::Int),
+                (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Int)),
+                ),
             ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .named("radix", SyntaxShape::Number, "radix of integer", Some('r'))
             .switch("little-endian", "use little-endian byte decoding", None)
             .rest(

crates/nu-command/src/conversions/into/string.rs

@@ -40,6 +40,10 @@ impl Command for SubCommand {
                 (Type::Bool, Type::String),
                 (Type::Filesize, Type::String),
                 (Type::Date, Type::String),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::String)),
+                ),
             ])
             .allow_variants_without_examples(true) // https://github.com/nushell/nushell/issues/7032
             .rest(

crates/nu-command/src/env/load_env.rs

@@ -19,7 +19,10 @@ impl Command for LoadEnv {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("load-env")
-            .input_output_types(vec![(Type::Record(vec![]), Type::Nothing)])
+            .input_output_types(vec![
+                (Type::Record(vec![]), Type::Nothing),
+                (Type::Nothing, Type::Nothing),
+            ])
             .allow_variants_without_examples(true)
             .optional(
                 "update",

crates/nu-command/src/filters/append.rs

@@ -16,11 +16,15 @@ impl Command for Append {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("append")
-            .input_output_types(vec![(
+            .input_output_types(vec![
+                (
                     Type::List(Box::new(Type::Any)),
                     Type::List(Box::new(Type::Any)),
-            )])
+                ),
+                (Type::Record(vec![]), Type::Table(vec![])),
+            ])
             .required("row", SyntaxShape::Any, "the row, list, or table to append")
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/each.rs

@@ -41,6 +41,7 @@ with 'transpose' first."#
                     Type::List(Box::new(Type::Any)),
                 ),
                 (Type::Table(vec![]), Type::List(Box::new(Type::Any))),
+                (Type::Any, Type::Any),
             ])
             .required(
                 "closure",
@@ -48,6 +49,7 @@ with 'transpose' first."#
                 "the closure to run",
             )
             .switch("keep-empty", "keep empty result cells", Some('k'))
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/find.rs

@@ -29,7 +29,7 @@ impl Command for Find {
                     Type::List(Box::new(Type::Any)),
                     Type::List(Box::new(Type::Any)),
                 ),
-                (Type::String, Type::String),
+                (Type::String, Type::Any),
                 (
                     // For find -p
                     Type::Table(vec![]),

crates/nu-command/src/filters/first.rs

@@ -33,12 +33,14 @@ impl Command for First {
                     Type::Any,
                 ),
                 (Type::Binary, Type::Binary),
+                (Type::Range, Type::Any),
             ])
             .optional(
                 "rows",
                 SyntaxShape::Int,
                 "starting from the front, the number of rows to return",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/get.rs

@@ -34,6 +34,7 @@ If multiple cell paths are given, this will produce a list of values."#
                     Type::Any,
                 ),
                 (Type::Table(vec![]), Type::Any),
+                (Type::Record(vec![]), Type::Any),
             ])
             .required(
                 "cell_path",
@@ -51,6 +52,7 @@ If multiple cell paths are given, this will produce a list of values."#
                 "get path in a case sensitive manner",
                 Some('s'),
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/insert.rs

@@ -19,6 +19,10 @@ impl Command for Insert {
             .input_output_types(vec![
                 (Type::Record(vec![]), Type::Record(vec![])),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
             ])
             .required(
                 "field",
@@ -30,6 +34,7 @@ impl Command for Insert {
                 SyntaxShape::Any,
                 "the new value to give the cell(s)",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/select.rs

@@ -21,6 +21,7 @@ impl Command for Select {
             .input_output_types(vec![
                 (Type::Record(vec![]), Type::Record(vec![])),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (Type::List(Box::new(Type::Any)), Type::Any),
             ])
             .switch(
                 "ignore-errors",
@@ -32,6 +33,7 @@ impl Command for Select {
                 SyntaxShape::CellPath,
                 "the columns to select from the table",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/sort_by.rs

@@ -16,7 +16,13 @@ impl Command for SortBy {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("sort-by")
-            .input_output_types(vec![(Type::Table(vec![]), Type::Table(vec![]))])
+            .input_output_types(vec![
+                (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
+            ])
             .rest("columns", SyntaxShape::Any, "the column(s) to sort by")
             .switch("reverse", "Sort in reverse order", Some('r'))
             .switch(
@@ -29,6 +35,7 @@ impl Command for SortBy {
                 "Sort alphanumeric string-based columns naturally (1, 9, 10, 99, 100, ...)",
                 Some('n'),
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/transpose.rs

@@ -29,6 +29,7 @@ impl Command for Transpose {
             .input_output_types(vec![
                 (Type::Table(vec![]), Type::Table(vec![])),
                 (Type::Table(vec![]), Type::Record(vec![])),
+                (Type::Record(vec![]), Type::Table(vec![])),
             ])
             .switch(
                 "header-row",
@@ -55,6 +56,7 @@ impl Command for Transpose {
                 "on repetition of record fields due to `header-row`, keep all the values obtained",
                 Some('a'),
             )
+            .allow_variants_without_examples(true)
             .rest(
                 "rest",
                 SyntaxShape::String,

crates/nu-command/src/filters/uniq_by.rs

@@ -17,7 +17,13 @@ impl Command for UniqBy {
 
     fn signature(&self) -> Signature {
         Signature::build("uniq-by")
-            .input_output_types(vec![(Type::Table(vec![]), Type::Table(vec![]))])
+            .input_output_types(vec![
+                (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
+            ])
             .rest("columns", SyntaxShape::Any, "the column(s) to filter by")
             .switch(
                 "count",
@@ -39,6 +45,7 @@ impl Command for UniqBy {
                 "Return the input values that occur once only",
                 Some('u'),
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/update.rs

@@ -19,6 +19,10 @@ impl Command for Update {
             .input_output_types(vec![
                 (Type::Record(vec![]), Type::Record(vec![])),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
             ])
             .required(
                 "field",
@@ -30,6 +34,7 @@ impl Command for Update {
                 SyntaxShape::Any,
                 "the new value to give the cell(s), or a closure to create the value",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/upsert.rs

@@ -19,6 +19,10 @@ impl Command for Upsert {
             .input_output_types(vec![
                 (Type::Record(vec![]), Type::Record(vec![])),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
             ])
             .required(
                 "field",
@@ -30,6 +34,7 @@ impl Command for Upsert {
                 SyntaxShape::Any,
                 "the new value to give the cell(s), or a closure to create the value",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/where_.rs

@@ -32,12 +32,14 @@ not supported."#
                     Type::List(Box::new(Type::Any)),
                 ),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (Type::Range, Type::Any),
             ])
             .required(
                 "row_condition",
                 SyntaxShape::RowCondition,
                 "Filter condition",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/filters/wrap.rs

@@ -23,8 +23,10 @@ impl Command for Wrap {
             .input_output_types(vec![
                 (Type::List(Box::new(Type::Any)), Type::Table(vec![])),
                 (Type::Range, Type::Table(vec![])),
+                (Type::Any, Type::Record(vec![])),
             ])
             .required("name", SyntaxShape::String, "the name of the column")
+            .allow_variants_without_examples(true)
             .category(Category::Filters)
     }
 

crates/nu-command/src/math/abs.rs

@@ -12,8 +12,15 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math abs")
-            .input_output_types(vec![(Type::Number, Type::Number)])
+            .input_output_types(vec![
+                (Type::Number, Type::Number),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/avg.rs

@@ -14,7 +14,12 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math avg")
-            .input_output_types(vec![(Type::List(Box::new(Type::Number)), Type::Number)])
+            .input_output_types(vec![
+                (Type::List(Box::new(Type::Number)), Type::Number),
+                (Type::List(Box::new(Type::Duration)), Type::Duration),
+                (Type::List(Box::new(Type::Filesize)), Type::Filesize),
+            ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/ceil.rs

@@ -12,8 +12,15 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math ceil")
-            .input_output_types(vec![(Type::Number, Type::Int)])
+            .input_output_types(vec![
+                (Type::Number, Type::Int),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/floor.rs

@@ -12,8 +12,15 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math floor")
-            .input_output_types(vec![(Type::Number, Type::Int)])
+            .input_output_types(vec![
+                (Type::Number, Type::Int),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/log.rs

@@ -20,7 +20,15 @@ impl Command for SubCommand {
                 SyntaxShape::Number,
                 "Base for which the logarithm should be computed",
             )
-            .input_output_types(vec![(Type::Number, Type::Float)])
+            .input_output_types(vec![
+                (Type::Number, Type::Float),
+                (Type::Number, Type::Int),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
+            .allow_variants_without_examples(true)
             .vectorizes_over_list(true)
             .category(Category::Math)
     }

crates/nu-command/src/math/max.rs

@@ -18,6 +18,7 @@ impl Command for SubCommand {
                 (Type::List(Box::new(Type::Number)), Type::Number),
                 (Type::Table(vec![]), Type::Record(vec![])),
             ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/median.rs

@@ -20,6 +20,7 @@ impl Command for SubCommand {
                 (Type::List(Box::new(Type::Number)), Type::Number),
                 (Type::Table(vec![]), Type::Record(vec![])),
             ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/min.rs

@@ -18,6 +18,7 @@ impl Command for SubCommand {
                 (Type::List(Box::new(Type::Number)), Type::Number),
                 (Type::Table(vec![]), Type::Record(vec![])),
             ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/mode.rs

@@ -45,6 +45,7 @@ impl Command for SubCommand {
                 ),
                 (Type::Table(vec![]), Type::Record(vec![])),
             ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/round.rs

@@ -15,7 +15,13 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math round")
-            .input_output_types(vec![(Type::Number, Type::Number)])
+            .input_output_types(vec![
+                (Type::Number, Type::Number),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .named(
                 "precision",

crates/nu-command/src/math/sqrt.rs

@@ -12,8 +12,15 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math sqrt")
-            .input_output_types(vec![(Type::Number, Type::Number)])
+            .input_output_types(vec![
+                (Type::Number, Type::Number),
+                (
+                    Type::List(Box::new(Type::Number)),
+                    Type::List(Box::new(Type::Number)),
+                ),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/math/sum.rs

@@ -14,7 +14,12 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("math sum")
-            .input_output_types(vec![(Type::List(Box::new(Type::Number)), Type::Number)])
+            .input_output_types(vec![
+                (Type::List(Box::new(Type::Number)), Type::Number),
+                (Type::Range, Type::Number),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
+            .allow_variants_without_examples(true)
             .category(Category::Math)
     }
 

crates/nu-command/src/network/url/encode.rs

@@ -17,7 +17,7 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("url encode")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![(Type::String, Type::String), (Type::List(Box::new(Type::String)), Type::List(Box::new(Type::String)))])
             .vectorizes_over_list(true)
             .switch(
             "all",

crates/nu-command/src/path/join.rs

@@ -35,6 +35,7 @@ impl Command for SubCommand {
             .input_output_types(vec![
                 (Type::String, Type::String),
                 (Type::List(Box::new(Type::String)), Type::String),
+                (Type::Record(vec![]), Type::String),
                 (Type::Table(vec![]), Type::List(Box::new(Type::String))),
             ])
             .named(
@@ -43,6 +44,7 @@ impl Command for SubCommand {
                 "For a record or table input, join strings at the given columns",
                 Some('c'),
             )
+            .allow_variants_without_examples(true)
             .rest("append", SyntaxShape::String, "Path to append to the input")
     }
 

crates/nu-command/src/platform/ansi/strip.rs

@@ -15,12 +15,13 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("ansi strip")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![(Type::String, Type::String), (Type::List(Box::new(Type::String)), Type::List(Box::new(Type::String)))])
             .rest(
                 "cell path",
                 SyntaxShape::CellPath,
                 "for a data structure input, remove ANSI sequences from strings at the given cell paths",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Platform)
     }
 

crates/nu-command/src/strings/parse.rs

@@ -30,8 +30,12 @@ impl Command for Parse {
                 SyntaxShape::String,
                 "the pattern to match. Eg) \"{foo}: {bar}\"",
             )
-            .input_output_types(vec![(Type::String, Type::Table(vec![]))])
+            .input_output_types(vec![
+                (Type::String, Type::Table(vec![])),
+                (Type::List(Box::new(Type::Any)), Type::Table(vec![])),
+            ])
             .switch("regex", "use full regex syntax for patterns", Some('r'))
+            .allow_variants_without_examples(true)
             .category(Category::Strings)
     }
 

crates/nu-command/src/strings/split/row.rs

@@ -16,8 +16,12 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("split row")
-            .input_output_types(vec![(Type::String, Type::List(Box::new(Type::String)))])
+            .input_output_types(vec![
+                (Type::String, Type::List(Box::new(Type::String))),
+                (Type::List(Box::new(Type::String)), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .required(
                 "separator",
                 SyntaxShape::String,

crates/nu-command/src/strings/str_/case/camel_case.rs

@@ -17,7 +17,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str camel-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/capitalize.rs

@@ -15,7 +15,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str capitalize")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/downcase.rs

@@ -15,7 +15,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str downcase")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/kebab_case.rs

@@ -17,7 +17,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str kebab-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/pascal_case.rs

@@ -17,7 +17,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str pascal-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/screaming_snake_case.rs

@@ -16,7 +16,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str screaming-snake-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/snake_case.rs

@@ -16,7 +16,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str snake-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/title_case.rs

@@ -17,7 +17,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str title-case")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/case/upcase.rs

@@ -14,8 +14,12 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str upcase")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .rest(
                 "rest",
                 SyntaxShape::CellPath,

crates/nu-command/src/strings/str_/contains.rs

@@ -32,6 +32,7 @@ impl Command for SubCommand {
             .input_output_types(vec![
                 (Type::String, Type::Bool),
                 (Type::Table(vec![]), Type::Table(vec![])),
+                (Type::List(Box::new(Type::String)), Type::List(Box::new(Type::Bool)))
             ])
             .vectorizes_over_list(true)
             .required("string", SyntaxShape::String, "the substring to find")

crates/nu-command/src/strings/str_/join.rs

@@ -16,12 +16,16 @@ impl Command for StrJoin {
 
     fn signature(&self) -> Signature {
         Signature::build("str join")
-            .input_output_types(vec![(Type::List(Box::new(Type::String)), Type::String)])
+            .input_output_types(vec![
+                (Type::List(Box::new(Type::Any)), Type::String),
+                (Type::String, Type::String),
+            ])
             .optional(
                 "separator",
                 SyntaxShape::String,
                 "optional separator to use when creating string",
             )
+            .allow_variants_without_examples(true)
             .category(Category::Strings)
     }
 

crates/nu-command/src/strings/str_/length.rs

@@ -29,7 +29,7 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str length")
-            .input_output_types(vec![(Type::String, Type::Int)])
+            .input_output_types(vec![(Type::String, Type::Int), (Type::List(Box::new(Type::String)), Type::List(Box::new(Type::Int)))])
             .vectorizes_over_list(true)
             .switch(
                 "grapheme-clusters",

crates/nu-command/src/strings/str_/replace.rs

@@ -34,7 +34,10 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str replace")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
             .required("find", SyntaxShape::String, "the pattern to find")
             .required("replace", SyntaxShape::String, "the replacement string")

crates/nu-command/src/strings/str_/reverse.rs

@@ -16,7 +16,13 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str reverse")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (
+                    Type::List(Box::new(Type::String)),
+                    Type::List(Box::new(Type::String)),
+                ),
+            ])
             .vectorizes_over_list(true)
             .rest(
                 "rest",

crates/nu-command/src/strings/str_/substring.rs

@@ -42,8 +42,9 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str substring")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![(Type::String, Type::String), (Type::Table(vec![]), Type::Table(vec![]))])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .switch(
                 "grapheme-clusters",
                 "count indexes and split using grapheme clusters (all visible chars have length 1)",

crates/nu-command/src/strings/str_/trim/trim_.rs

@@ -35,8 +35,16 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str trim")
-            .input_output_types(vec![(Type::String, Type::String)])
+            .input_output_types(vec![
+                (Type::String, Type::String),
+                (
+                    Type::List(Box::new(Type::String)),
+                    Type::List(Box::new(Type::String)),
+                ),
+                (Type::Table(vec![]), Type::Table(vec![])),
+            ])
             .vectorizes_over_list(true)
+            .allow_variants_without_examples(true)
             .rest(
                 "rest",
                 SyntaxShape::CellPath,

crates/nu-command/tests/commands/drop.rs

@@ -91,5 +91,5 @@ fn nth_missing_first_argument() {
 fn fail_on_non_iterator() {
     let actual = nu!("1 | drop 50");
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/last.rs

@@ -78,7 +78,7 @@ fn last_errors_on_negative_index() {
 fn fail_on_non_iterator() {
     let actual = nu!("1 | last");
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }
 
 #[test]

crates/nu-command/tests/commands/math/round.rs

@@ -32,5 +32,5 @@ fn can_round_float_with_negative_precision() {
 fn fails_with_wrong_input_type() {
     let actual = nu!("\"not_a_number\" | math round");
 
-    assert!(actual.err.contains("Input type not supported"))
+    assert!(actual.err.contains("command doesn't support"))
 }

crates/nu-command/tests/commands/mkdir.rs

@@ -70,7 +70,6 @@ fn print_created_paths() {
          pipeline(
              r#"
                  mkdir -v dir_1 dir_2 dir_3
-                 | length
              "#
         ));
 

crates/nu-command/tests/commands/rename.rs

@@ -83,7 +83,7 @@ fn errors_if_no_columns_present() {
                 "#
         ));
 
-        assert!(actual.err.contains("only record input data is supported"));
+        assert!(actual.err.contains("command doesn't support"));
     })
 }
 

crates/nu-command/tests/commands/reverse.rs

@@ -14,5 +14,5 @@ fn can_get_reverse_first() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | reverse"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/skip/skip_.rs

@@ -19,5 +19,5 @@ fn binary_skip() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | skip 2"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/skip/until.rs

@@ -54,5 +54,5 @@ fn condition_is_met() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | skip until {|row| $row == 2}"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/skip/while_.rs

@@ -54,5 +54,5 @@ fn condition_is_met() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | skip while {|row| $row == 2}"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/sort_by.rs

@@ -126,5 +126,5 @@ fn no_column_specified_fails() {
 fn fail_on_non_iterator() {
     let actual = nu!("1 | sort-by");
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/take/rows.rs

@@ -51,7 +51,7 @@ fn fails_on_string() {
             "#
     ));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }
 
 #[test]

crates/nu-command/tests/commands/take/until.rs

@@ -55,5 +55,5 @@ fn condition_is_met() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | take until {|row| $row == 2}"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/take/while_.rs

@@ -54,5 +54,5 @@ fn condition_is_met() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline("1 | take while {|row| $row == 2}"));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }

crates/nu-command/tests/commands/where_.rs

@@ -180,7 +180,7 @@ fn contains_operator() {
 fn fail_on_non_iterator() {
     let actual = nu!(cwd: ".", pipeline(r#"{"name": "foo", "size": 3} | where name == "foo""#));
 
-    assert!(actual.err.contains("only_supports_this_input_type"));
+    assert!(actual.err.contains("command doesn't support"));
 }
 
 // Test that filtering on columns that might be missing/null works

crates/nu-command/tests/format_conversions/csv.rs

@@ -405,5 +405,5 @@ fn string_to_csv_error() {
         "#
     ));
 
-    assert!(actual.err.contains("can't convert"))
+    assert!(actual.err.contains("command doesn't support"))
 }

crates/nu-command/tests/format_conversions/toml.rs

@@ -70,7 +70,7 @@ fn table_to_toml_fails() {
         "#
     ));
 
-    assert_eq!(actual.out, "true");
+    assert!(actual.err.contains("command doesn't support"));
 }
 
 #[test]
@@ -83,7 +83,7 @@ fn string_to_toml_fails() {
         "#
     ));
 
-    assert_eq!(actual.out, "true");
+    assert!(actual.err.contains("command doesn't support"));
 }
 
 #[test]

crates/nu-parser/src/parser.rs

@@ -4,7 +4,7 @@ use crate::{
     lite_parser::{lite_parse, LiteCommand, LiteElement, LitePipeline},
     parse_mut,
     parse_patterns::{parse_match_pattern, parse_pattern},
-    type_check::{math_result_type, type_compatible},
+    type_check::{self, math_result_type, type_compatible},
     Token, TokenContents,
 };
 
@@ -5582,6 +5582,8 @@ pub fn parse_block(
 
     block.span = Some(span);
 
+    type_check::check_block_input_output(working_set, &block);
+
     block
 }
 

crates/nu-parser/src/type_check.rs

@@ -1,5 +1,8 @@
 use nu_protocol::{
-    ast::{Bits, Boolean, Comparison, Expr, Expression, Math, Operator},
+    ast::{
+        Bits, Block, Boolean, Comparison, Expr, Expression, Math, Operator, Pipeline,
+        PipelineElement,
+    },
     engine::StateWorkingSet,
     ParseError, Type,
 };
@@ -24,7 +27,30 @@ pub fn type_compatible(lhs: &Type, rhs: &Type) -> bool {
 
     match (lhs, rhs) {
         (Type::List(c), Type::List(d)) => type_compatible(c, d),
-        (Type::List(c), Type::Table(_)) => matches!(**c, Type::Any),
+        (Type::ListStream, Type::List(_)) => true,
+        (Type::List(_), Type::ListStream) => true,
+        (Type::List(c), Type::Table(table_fields)) => {
+            if matches!(**c, Type::Any) {
+                return true;
+            }
+
+            if let Type::Record(fields) = &**c {
+                is_compatible(fields, table_fields)
+            } else {
+                false
+            }
+        }
+        (Type::Table(table_fields), Type::List(c)) => {
+            if matches!(**c, Type::Any) {
+                return true;
+            }
+
+            if let Type::Record(fields) = &**c {
+                is_compatible(table_fields, fields)
+            } else {
+                false
+            }
+        }
         (Type::Number, Type::Int) => true,
         (Type::Int, Type::Number) => true,
         (Type::Number, Type::Float) => true,
@@ -921,3 +947,108 @@ pub fn math_result_type(
         }
     }
 }
+
+pub fn check_pipeline_type(
+    working_set: &mut StateWorkingSet,
+    pipeline: &Pipeline,
+    input_type: Type,
+) -> Type {
+    let mut current_type = input_type;
+
+    'elem: for elem in &pipeline.elements {
+        match elem {
+            PipelineElement::Expression(
+                _,
+                Expression {
+                    expr: Expr::Call(call),
+                    ..
+                },
+            ) => {
+                let decl = working_set.get_decl(call.decl_id);
+
+                if current_type == Type::Any {
+                    let mut new_current_type = None;
+                    for (_, call_output) in decl.signature().input_output_types {
+                        if let Some(inner_current_type) = &new_current_type {
+                            if inner_current_type == &Type::Any {
+                                break;
+                            } else if inner_current_type != &call_output {
+                                // Union unequal types to Any for now
+                                new_current_type = Some(Type::Any)
+                            }
+                        } else {
+                            new_current_type = Some(call_output.clone())
+                        }
+                    }
+
+                    if let Some(new_current_type) = new_current_type {
+                        current_type = new_current_type
+                    } else {
+                        current_type = Type::Any;
+                    }
+                    continue 'elem;
+                } else {
+                    for (call_input, call_output) in decl.signature().input_output_types {
+                        if type_compatible(&call_input, &current_type) {
+                            current_type = call_output.clone();
+                            continue 'elem;
+                        }
+                    }
+                }
+
+                if !decl.signature().input_output_types.is_empty() {
+                    working_set.error(ParseError::InputMismatch(current_type, call.head))
+                }
+                current_type = Type::Any;
+            }
+            PipelineElement::Expression(_, Expression { ty, .. }) => {
+                current_type = ty.clone();
+            }
+            _ => {
+                current_type = Type::Any;
+            }
+        }
+    }
+
+    current_type
+}
+
+pub fn check_block_input_output(working_set: &mut StateWorkingSet, block: &Block) {
+    // let inputs = block.input_types();
+
+    for (input_type, output_type) in &block.signature.input_output_types {
+        let mut current_type = input_type.clone();
+        let mut current_output_type = Type::Nothing;
+
+        for pipeline in &block.pipelines {
+            current_output_type = check_pipeline_type(working_set, pipeline, current_type);
+            current_type = Type::Nothing;
+        }
+
+        if !type_compatible(output_type, &current_output_type)
+            && output_type != &Type::Any
+            && current_output_type != Type::Any
+        {
+            working_set.error(ParseError::OutputMismatch(
+                output_type.clone(),
+                block
+                    .pipelines
+                    .last()
+                    .expect("internal error: we should have pipelines")
+                    .elements
+                    .last()
+                    .expect("internal error: we should have elements")
+                    .span(),
+            ))
+        }
+    }
+
+    if block.signature.input_output_types.is_empty() {
+        let mut current_type = Type::Any;
+
+        for pipeline in &block.pipelines {
+            let _ = check_pipeline_type(working_set, pipeline, current_type);
+            current_type = Type::Nothing;
+        }
+    }
+}

crates/nu-protocol/src/ast/block.rs

@@ -1,5 +1,5 @@
-use super::{Expr, Expression, Pipeline};
+use super::Pipeline;
-use crate::{ast::PipelineElement, engine::StateWorkingSet, Signature, Span, Type, VarId};
+use crate::{ast::PipelineElement, Signature, Span, Type, VarId};
 use serde::{Deserialize, Serialize};
 use std::ops::{Index, IndexMut};
 
@@ -66,37 +66,6 @@ impl Block {
         }
     }
 
-    pub fn input_type(&self, working_set: &StateWorkingSet) -> Type {
-        if let Some(first) = self.pipelines.first() {
-            if let Some(first) = first.elements.first() {
-                match first {
-                    PipelineElement::Expression(
-                        _,
-                        Expression {
-                            expr: Expr::Call(call),
-                            ..
-                        },
-                    ) => {
-                        let decl = working_set.get_decl(call.decl_id);
-
-                        decl.signature().get_input_type()
-                    }
-                    PipelineElement::Expression(
-                        _,
-                        Expression {
-                            expr: Expr::ExternalCall(..),
-                            ..
-                        },
-                    ) => Type::Any,
-                    _ => Type::Nothing,
-                }
-            } else {
-                Type::Nothing
-            }
-        } else {
-            Type::Nothing
-        }
-    }
     pub fn output_type(&self) -> Type {
         if let Some(last) = self.pipelines.last() {
             if let Some(last) = last.elements.last() {

crates/nu-protocol/src/parse_error.rs

@@ -48,6 +48,14 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::parse_mismatch_with_full_string_msg))]
     ExpectedWithStringMsg(String, #[label("expected {0}")] Span),
 
+    #[error("Command does not support {0} input.")]
+    #[diagnostic(code(nu::parser::input_type_mismatch))]
+    InputMismatch(Type, #[label("command doesn't support {0} input")] Span),
+
+    #[error("Command output doesn't match {0}.")]
+    #[diagnostic(code(nu::parser::output_type_mismatch))]
+    OutputMismatch(Type, #[label("command doesn't output {0}")] Span),
+
     #[error("Type mismatch during operation.")]
     #[diagnostic(code(nu::parser::type_mismatch))]
     Mismatch(String, String, #[label("expected {0}, found {1}")] Span), // expected, found, span
@@ -526,6 +534,8 @@ impl ParseError {
             ParseError::KeywordMissingArgument(_, _, s) => *s,
             ParseError::MissingType(s) => *s,
             ParseError::TypeMismatch(_, _, s) => *s,
+            ParseError::InputMismatch(_, s) => *s,
+            ParseError::OutputMismatch(_, s) => *s,
             ParseError::MissingRequiredFlag(_, s) => *s,
             ParseError::IncompleteMathExpression(s) => *s,
             ParseError::UnknownState(_, s) => *s,

src/tests/test_bits.rs

@@ -46,7 +46,7 @@ fn bits_xor_negative() -> TestResult {
 #[test]
 fn bits_xor_list() -> TestResult {
     run_test(
-        "[1 2 3 8 9 10] | bits xor 2 | str join '.'",
+        "[1 2 3 8 9 10] | bits xor 2 | into string | str join '.'",
         "3.0.1.10.11.8",
     )
 }

src/tests/test_engine.rs

@@ -55,7 +55,7 @@ fn in_and_if_else() -> TestResult {
 #[test]
 fn help_works_with_missing_requirements() -> TestResult {
     // `each while` is part of the *extra* feature and adds 3 lines
-    let expected_length = if cfg!(feature = "extra") { "65" } else { "62" };
+    let expected_length = if cfg!(feature = "extra") { "66" } else { "63" };
     run_test(r#"each --help | lines | length"#, expected_length)
 }