Improve type hovers (#9515)

# Description

This PR does a few things to help improve type hovers and, in the
process, fixes a few outstanding issues in the type system. Here's a
list of the changes:

* `for` now will try to infer the type of the iteration variable based
on the expression it's given. This fixes things like `for x in [1, 2, 3]
{ }` where `x` now properly gets the int type.
* Removed old input/output type fields from the signature, focuses on
the vec of signatures. Updated a bunch of dataframe commands that hadn't
moved over. This helps tie things together a bit better
* Fixed inference of types from subexpressions to use the last
expression in the block
* Fixed handling of explicit types in `let` and `mut` calls, so we now
respect that as the authoritative type

I also tried to add `def` input/output type inference, but unfortunately
we only know the predecl types universally, which means we won't have
enough information to properly know what the types of the custom
commands are.

# User-Facing Changes

Script typechecking will get tighter in some cases
Hovers should be more accurate in some cases that previously resorted to
any.

# Tests + Formatting
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---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-cmd-dataframe/src/dataframe/series/all_false.rs

@@ -20,8 +20,10 @@ impl Command for AllFalse {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/all_true.rs

@@ -20,8 +20,10 @@ impl Command for AllTrue {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/arg_max.rs

@@ -25,8 +25,10 @@ impl Command for ArgMax {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/arg_min.rs

@@ -25,8 +25,10 @@ impl Command for ArgMin {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/cumulative.rs

@@ -56,8 +56,10 @@ impl Command for Cumulative {
         Signature::build(self.name())
             .required("type", SyntaxShape::String, "rolling operation")
             .switch("reverse", "Reverse cumulative calculation", Some('r'))
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/as_date.rs

@@ -31,9 +31,11 @@ impl Command for AsDate {
         Signature::build(self.name())
             .required("format", SyntaxShape::String, "formatting date string")
             .switch("not-exact", "the format string may be contained in the date (e.g. foo-2021-01-01-bar could match 2021-01-01)", Some('n'))
-                        .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
-.category(Category::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
+            .category(Category::Custom("dataframe".into()))
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-cmd-dataframe/src/dataframe/series/date/as_datetime.rs

@@ -40,9 +40,11 @@ impl Command for AsDateTime {
         Signature::build(self.name())
             .required("format", SyntaxShape::String, "formatting date time string")
             .switch("not-exact", "the format string may be contained in the date (e.g. foo-2021-01-01-bar could match 2021-01-01)", Some('n'))
-                        .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
-.category(Category::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
+            .category(Category::Custom("dataframe".into()))
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-cmd-dataframe/src/dataframe/series/date/get_day.rs

@@ -21,8 +21,10 @@ impl Command for GetDay {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_hour.rs

@@ -21,8 +21,10 @@ impl Command for GetHour {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_minute.rs

@@ -21,8 +21,10 @@ impl Command for GetMinute {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_month.rs

@@ -21,8 +21,10 @@ impl Command for GetMonth {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_nanosecond.rs

@@ -21,8 +21,10 @@ impl Command for GetNanosecond {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_ordinal.rs

@@ -21,8 +21,10 @@ impl Command for GetOrdinal {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_second.rs

@@ -21,8 +21,10 @@ impl Command for GetSecond {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_week.rs

@@ -21,8 +21,10 @@ impl Command for GetWeek {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_weekday.rs

@@ -21,8 +21,10 @@ impl Command for GetWeekDay {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/date/get_year.rs

@@ -21,8 +21,10 @@ impl Command for GetYear {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/indexes/arg_sort.rs

@@ -27,8 +27,10 @@ impl Command for ArgSort {
         Signature::build(self.name())
             .switch("reverse", "reverse order", Some('r'))
             .switch("nulls-last", "nulls ordered last", Some('n'))
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/indexes/arg_true.rs

@@ -25,8 +25,10 @@ impl Command for ArgTrue {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/indexes/arg_unique.rs

@@ -25,8 +25,10 @@ impl Command for ArgUnique {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/indexes/set_with_idx.rs

@@ -29,8 +29,10 @@ impl Command for SetWithIndex {
                 "list of indices indicating where to set the value",
                 Some('i'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/is_duplicated.rs

@@ -21,8 +21,10 @@ impl Command for IsDuplicated {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/is_in.rs

@@ -23,8 +23,10 @@ impl Command for IsIn {
     fn signature(&self) -> Signature {
         Signature::build(self.name())
             .required("other", SyntaxShape::Any, "right series")
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/is_not_null.rs

@@ -20,8 +20,10 @@ impl Command for IsNotNull {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/is_null.rs

@@ -20,8 +20,10 @@ impl Command for IsNull {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/is_unique.rs

@@ -21,8 +21,10 @@ impl Command for IsUnique {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/not.rs

@@ -22,8 +22,10 @@ impl Command for NotSeries {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/masks/set.rs

@@ -29,8 +29,10 @@ impl Command for SetSeries {
                 "mask indicating insertions",
                 Some('m'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/n_null.rs

@@ -20,8 +20,10 @@ impl Command for NNull {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/n_unique.rs

@@ -19,8 +19,10 @@ impl Command for NUnique {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/rolling.rs

@@ -59,8 +59,10 @@ impl Command for Rolling {
         Signature::build(self.name())
             .required("type", SyntaxShape::String, "rolling operation")
             .required("window", SyntaxShape::Int, "Window size for rolling")
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/shift.rs

@@ -30,8 +30,10 @@ impl Command for Shift {
                 "Expression used to fill the null values (lazy df)",
                 Some('f'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe or lazyframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/concatenate.rs

@@ -27,8 +27,10 @@ impl Command for Concatenate {
                 SyntaxShape::Any,
                 "Other array with string to be concatenated",
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/contains.rs

@@ -27,8 +27,10 @@ impl Command for Contains {
                 SyntaxShape::String,
                 "Regex pattern to be searched",
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/replace.rs

@@ -34,8 +34,10 @@ impl Command for Replace {
                 "replacing string",
                 Some('r'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/replace_all.rs

@@ -34,8 +34,10 @@ impl Command for ReplaceAll {
                 "replacing string",
                 Some('r'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/str_lengths.rs

@@ -21,8 +21,10 @@ impl Command for StrLengths {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/str_slice.rs

@@ -24,8 +24,10 @@ impl Command for StrSlice {
         Signature::build(self.name())
             .required("start", SyntaxShape::Int, "start of slice")
             .named("length", SyntaxShape::Int, "optional length", Some('l'))
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/strftime.rs

@@ -23,8 +23,10 @@ impl Command for StrFTime {
     fn signature(&self) -> Signature {
         Signature::build(self.name())
             .required("fmt", SyntaxShape::String, "Format rule")
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/to_lowercase.rs

@@ -21,8 +21,10 @@ impl Command for ToLowerCase {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/string/to_uppercase.rs

@@ -25,8 +25,10 @@ impl Command for ToUpperCase {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/unique.rs

@@ -40,8 +40,10 @@ impl Command for Unique {
                 "Keep the same order as the original DataFrame (lazy df)",
                 Some('k'),
             )
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe or lazyframe".into()))
     }
 

crates/nu-cmd-dataframe/src/dataframe/series/value_counts.rs

@@ -22,8 +22,10 @@ impl Command for ValueCount {
 
     fn signature(&self) -> Signature {
         Signature::build(self.name())
-            .input_type(Type::Custom("dataframe".into()))
-            .output_type(Type::Custom("dataframe".into()))
+            .input_output_type(
+                Type::Custom("dataframe".into()),
+                Type::Custom("dataframe".into()),
+            )
             .category(Category::Custom("dataframe".into()))
     }