Declare input and output types of commands (#6796)

* Add failing test that list of ints and floats is List<Number>

* Start defining subtype relation

* Make it possible to declare input and output types for commands

- Enforce them in tests

* Declare input and output types of commands

* Add formatted signatures to `help commands` table

* Revert SyntaxShape::Table -> Type::Table change

* Revert unnecessary derive(Hash) on SyntaxShape

Co-authored-by: JT <547158+jntrnr@users.noreply.github.com>

crates/nu-command/src/core_commands/alias.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct Alias;
@@ -16,6 +16,7 @@ impl Command for Alias {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("alias")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("name", SyntaxShape::String, "name of the alias")
             .required(
                 "initial_value",
@@ -53,12 +54,12 @@ impl Command for Alias {
             Example {
                 description: "Alias ll to ls -l",
                 example: "alias ll = ls -l",
-                result: None,
+                result: Some(Value::nothing(Span::test_data())),
             },
             Example {
                 description: "Make an alias that makes a list of all custom commands",
                 example: "alias customs = ($nu.scope.commands | where is_custom | get command)",
-                result: None,
+                result: Some(Value::nothing(Span::test_data())),
             },
         ]
     }

crates/nu-command/src/core_commands/ast.rs

@@ -3,7 +3,8 @@ use nu_parser::parse;
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack, StateWorkingSet},
-    Category, Example, PipelineData, ShellError, Signature, Spanned, SyntaxShape,
+    Category, Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Type,
+    Value,
 };
 
 #[derive(Clone)]
@@ -20,6 +21,7 @@ impl Command for Ast {
 
     fn signature(&self) -> Signature {
         Signature::build("ast")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required(
                 "pipeline",
                 SyntaxShape::String,
@@ -50,17 +52,17 @@ impl Command for Ast {
             Example {
                 description: "Print the ast of a string",
                 example: "ast 'hello'",
-                result: None,
+                result: Some(Value::nothing(Span::test_data())),
             },
             Example {
                 description: "Print the ast of a pipeline",
                 example: "ast 'ls | where name =~ README'",
-                result: None,
+                result: Some(Value::nothing(Span::test_data())),
             },
             Example {
                 description: "Print the ast of a pipeline with an error",
                 example: "ast 'for x in 1..10 { echo $x '",
-                result: None,
+                result: Some(Value::nothing(Span::test_data())),
             },
         ]
     }

crates/nu-command/src/core_commands/commandline.rs

@@ -4,7 +4,7 @@ use nu_protocol::engine::ReplOperation;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::Category;
 use nu_protocol::IntoPipelineData;
-use nu_protocol::{PipelineData, ShellError, Signature, SyntaxShape, Value};
+use nu_protocol::{PipelineData, ShellError, Signature, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct Commandline;
@@ -16,6 +16,7 @@ impl Command for Commandline {
 
     fn signature(&self) -> Signature {
         Signature::build("commandline")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .switch(
                 "append",
                 "appends the string to the end of the buffer",

crates/nu-command/src/core_commands/debug.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Span, Value};
+use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Span, Type, Value};
 
 #[derive(Clone)]
 pub struct Debug;
@@ -15,11 +15,17 @@ impl Command for Debug {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("debug").category(Category::Core).switch(
-            "raw",
-            "Prints the raw value representation",
-            Some('r'),
-        )
+        Signature::build("debug")
+            .input_output_types(vec![
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::String)),
+                ),
+                (Type::Table(vec![]), Type::List(Box::new(Type::String))),
+                (Type::Any, Type::String),
+            ])
+            .category(Category::Core)
+            .switch("raw", "Prints the raw value representation", Some('r'))
     }
 
     fn run(
@@ -54,12 +60,20 @@ impl Command for Debug {
     fn examples(&self) -> Vec<Example> {
         vec![
             Example {
-                description: "Print the value of a string",
+                description: "Debug print a string",
                 example: "'hello' | debug",
                 result: Some(Value::test_string("hello")),
             },
             Example {
-                description: "Print the value of a table",
+                description: "Debug print a list",
+                example: "['hello'] | debug",
+                result: Some(Value::List {
+                    vals: vec![Value::test_string("hello")],
+                    span: Span::test_data(),
+                }),
+            },
+            Example {
+                description: "Debug print a table",
                 example: "echo [[version patch]; [0.1.0 false] [0.1.1 true] [0.2.0 false]] | debug",
                 result: Some(Value::List {
                     vals: vec![

crates/nu-command/src/core_commands/def.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct Def;
@@ -16,6 +16,7 @@ impl Command for Def {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("def")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("def_name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .required(

crates/nu-command/src/core_commands/def_env.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct DefEnv;
@@ -16,6 +16,7 @@ impl Command for DefEnv {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("def-env")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("def_name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .required(

crates/nu-command/src/core_commands/describe.rs

@@ -1,7 +1,7 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Value,
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
 };
 
 #[derive(Clone)]
@@ -17,7 +17,9 @@ impl Command for Describe {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("describe").category(Category::Core)
+        Signature::build("describe")
+            .input_output_types(vec![(Type::Any, Type::String)])
+            .category(Category::Core)
     }
 
     fn run(

crates/nu-command/src/core_commands/do_.rs

@@ -3,7 +3,7 @@ use nu_protocol::ast::Call;
 use nu_protocol::engine::{CaptureBlock, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, ListStream, PipelineData, RawStream, ShellError, Signature, SyntaxShape,
-    Value,
+    Type, Value,
 };
 
 #[derive(Clone)]
@@ -20,6 +20,7 @@ impl Command for Do {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("do")
+            .input_output_types(vec![(Type::Any, Type::Any)])
             .required("block", SyntaxShape::Any, "the block to run")
             .switch(
                 "ignore-errors",
@@ -197,8 +198,13 @@ impl Command for Do {
             },
             Example {
                 description: "Run the block, with a positional parameter",
-                example: r#"do {|x| 100 + $x } 50"#,
-                result: Some(Value::test_int(150)),
+                example: r#"do {|x| 100 + $x } 77"#,
+                result: Some(Value::test_int(177)),
+            },
+            Example {
+                description: "Run the block, with input",
+                example: r#"77 | do {|x| 100 + $in }"#,
+                result: None, // TODO: returns 177
             },
         ]
     }

crates/nu-command/src/core_commands/echo.rs

@@ -2,7 +2,8 @@ use nu_engine::CallExt;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, ListStream, PipelineData, ShellError, Signature, Span, SyntaxShape, Value,
+    Category, Example, ListStream, PipelineData, ShellError, Signature, Span, SyntaxShape, Type,
+    Value,
 };
 
 #[derive(Clone)]
@@ -19,6 +20,7 @@ impl Command for Echo {
 
     fn signature(&self) -> Signature {
         Signature::build("echo")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
             .rest("rest", SyntaxShape::Any, "the values to echo")
             .category(Category::Core)
     }

crates/nu-command/src/core_commands/export.rs

@@ -2,7 +2,7 @@ use nu_engine::get_full_help;
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, Example, IntoPipelineData, PipelineData, Signature, Span, Value,
+    Category, Example, IntoPipelineData, PipelineData, Signature, Span, Type, Value,
 };
 
 #[derive(Clone)]
@@ -14,7 +14,9 @@ impl Command for ExportCommand {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("export").category(Category::Core)
+        Signature::build("export")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .category(Category::Core)
     }
 
     fn usage(&self) -> &str {

crates/nu-command/src/core_commands/export_alias.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type};
 
 #[derive(Clone)]
 pub struct ExportAlias;
@@ -16,6 +16,7 @@ impl Command for ExportAlias {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export alias")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("name", SyntaxShape::String, "name of the alias")
             .required(
                 "initial_value",

crates/nu-command/src/core_commands/export_def.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct ExportDef;
@@ -16,6 +16,7 @@ impl Command for ExportDef {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export def")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .required(

crates/nu-command/src/core_commands/export_def_env.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct ExportDefEnv;
@@ -16,6 +16,7 @@ impl Command for ExportDefEnv {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export def-env")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .required(

crates/nu-command/src/core_commands/export_extern.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type};
 
 #[derive(Clone)]
 pub struct ExportExtern;
@@ -16,6 +16,7 @@ impl Command for ExportExtern {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export extern")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("def_name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .category(Category::Core)

crates/nu-command/src/core_commands/export_use.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct ExportUse;
@@ -16,6 +16,7 @@ impl Command for ExportUse {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export use")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("pattern", SyntaxShape::ImportPattern, "import pattern")
             .category(Category::Core)
     }

crates/nu-command/src/core_commands/extern_.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type};
 
 #[derive(Clone)]
 pub struct Extern;
@@ -16,6 +16,7 @@ impl Command for Extern {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("extern")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("def_name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .category(Category::Core)

crates/nu-command/src/core_commands/for_.rs

@@ -3,7 +3,7 @@ use nu_protocol::ast::Call;
 use nu_protocol::engine::{CaptureBlock, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoInterruptiblePipelineData, ListStream, PipelineData, Signature, Span,
-    SyntaxShape, Value,
+    SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -20,6 +20,7 @@ impl Command for For {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("for")
+            .input_output_types(vec![(Type::Nothing, Type::List(Box::new(Type::Any)))])
             .required(
                 "var_name",
                 SyntaxShape::VarWithOptType,

crates/nu-command/src/core_commands/help.rs

@@ -1,4 +1,5 @@
 use fancy_regex::Regex;
+use itertools::Itertools;
 use nu_ansi_term::{
     Color::{Default, Red, White},
     Style,
@@ -9,7 +10,7 @@ use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
     span, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
-    ShellError, Signature, Span, Spanned, SyntaxShape, Value,
+    ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
 };
 use std::borrow::Borrow;
 #[derive(Clone)]
@@ -22,6 +23,7 @@ impl Command for Help {
 
     fn signature(&self) -> Signature {
         Signature::build("help")
+            .input_output_types(vec![(Type::Nothing, Type::String)])
             .rest(
                 "rest",
                 SyntaxShape::String,
@@ -162,6 +164,16 @@ fn help(
                     span: head,
                 });
 
+                cols.push("signatures".into());
+                vals.push(Value::String {
+                    val: sig
+                        .input_output_types
+                        .iter()
+                        .map(|(i, o)| format!("{:?} => {:?}", i.to_shape(), o.to_shape()))
+                        .join("\n"),
+                    span: head,
+                });
+
                 cols.push("search_terms".into());
                 vals.push(if search_terms.is_empty() {
                     Value::nothing(head)
@@ -259,6 +271,16 @@ fn help(
                     span: head,
                 });
 
+                cols.push("signatures".into());
+                vals.push(Value::String {
+                    val: sig
+                        .input_output_types
+                        .iter()
+                        .map(|(i, o)| format!("{:?} => {:?}", i.to_shape(), o.to_shape()))
+                        .join("\n"),
+                    span: head,
+                });
+
                 cols.push("search_terms".into());
                 vals.push(if search_terms.is_empty() {
                     Value::nothing(head)

crates/nu-command/src/core_commands/hide.rs

@@ -1,7 +1,7 @@
 use nu_protocol::ast::{Call, Expr, Expression};
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Value,
+    Category, Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -14,6 +14,7 @@ impl Command for Hide {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("hide")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("pattern", SyntaxShape::ImportPattern, "import pattern")
             .category(Category::Core)
     }

crates/nu-command/src/core_commands/hide_env.rs

@@ -3,7 +3,7 @@ use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     did_you_mean, Category, Example, PipelineData, ShellError, Signature, Span, Spanned,
-    SyntaxShape, Value,
+    SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -16,6 +16,7 @@ impl Command for HideEnv {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("hide-env")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .rest(
                 "name",
                 SyntaxShape::String,

crates/nu-command/src/core_commands/if_.rs

@@ -2,7 +2,7 @@ use nu_engine::{eval_block, eval_expression, eval_expression_with_input, CallExt
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{CaptureBlock, Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, FromValue, PipelineData, ShellError, Signature, SyntaxShape, Value,
+    Category, Example, FromValue, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -19,6 +19,7 @@ impl Command for If {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("if")
+            .input_output_types(vec![(Type::Any, Type::Any)])
             .required("cond", SyntaxShape::Expression, "condition to check")
             .required(
                 "then_block",

crates/nu-command/src/core_commands/ignore.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, Type, Value};
 
 #[derive(Clone)]
 pub struct Ignore;
@@ -15,7 +15,9 @@ impl Command for Ignore {
     }
 
     fn signature(&self) -> nu_protocol::Signature {
-        Signature::build("ignore").category(Category::Core)
+        Signature::build("ignore")
+            .input_output_types(vec![(Type::Any, Type::Nothing)])
+            .category(Category::Core)
     }
 
     fn search_terms(&self) -> Vec<&str> {
@@ -37,7 +39,7 @@ impl Command for Ignore {
         vec![Example {
             description: "Ignore the output of an echo command",
             example: "echo done | ignore",
-            result: None,
+            result: Some(Value::nothing(Span::test_data())),
         }]
     }
 }

crates/nu-command/src/core_commands/let_.rs

@@ -1,7 +1,7 @@
 use nu_engine::eval_expression_with_input;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type};
 
 #[derive(Clone)]
 pub struct Let;
@@ -17,6 +17,8 @@ impl Command for Let {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("let")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .allow_variants_without_examples(true)
             .required("var_name", SyntaxShape::VarWithOptType, "variable name")
             .required(
                 "initial_value",

crates/nu-command/src/core_commands/metadata.rs

@@ -3,7 +3,7 @@ use nu_protocol::ast::{Call, Expr, Expression};
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, DataSource, Example, IntoPipelineData, PipelineData, PipelineMetadata, Signature,
-    Span, SyntaxShape, Value,
+    Span, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -20,6 +20,8 @@ impl Command for Metadata {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("metadata")
+            .input_output_types(vec![(Type::Nothing, Type::Record(vec![]))])
+            .allow_variants_without_examples(true)
             .optional(
                 "expression",
                 SyntaxShape::Any,

crates/nu-command/src/core_commands/module.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Value};
+use nu_protocol::{Category, Example, PipelineData, Signature, Span, SyntaxShape, Type, Value};
 
 #[derive(Clone)]
 pub struct Module;
@@ -16,6 +16,7 @@ impl Command for Module {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("module")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("module_name", SyntaxShape::String, "module name")
             .required(
                 "block",

crates/nu-command/src/core_commands/register.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape};
+use nu_protocol::{Category, Example, PipelineData, Signature, SyntaxShape, Type};
 
 #[derive(Clone)]
 pub struct Register;
@@ -16,6 +16,7 @@ impl Command for Register {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("register")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required(
                 "plugin",
                 SyntaxShape::Filepath,

crates/nu-command/src/core_commands/use_.rs

@@ -2,7 +2,7 @@ use nu_engine::{eval_block, find_in_dirs_env, redirect_env};
 use nu_protocol::ast::{Call, Expr, Expression};
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Value,
+    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -19,6 +19,7 @@ impl Command for Use {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("use")
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("pattern", SyntaxShape::ImportPattern, "import pattern")
             .category(Category::Core)
     }

crates/nu-command/src/core_commands/version.rs

@@ -1,6 +1,6 @@
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Example, IntoPipelineData, PipelineData, ShellError, Signature, Value};
+use nu_protocol::{Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value};
 
 pub mod shadow {
     include!(concat!(env!("OUT_DIR"), "/shadow.rs"));
@@ -16,6 +16,8 @@ impl Command for Version {
 
     fn signature(&self) -> Signature {
         Signature::build("version")
+            .input_output_types(vec![(Type::Nothing, Type::Record(vec![]))])
+            .allow_variants_without_examples(true)
     }
 
     fn usage(&self) -> &str {
@@ -215,3 +217,13 @@ fn features_enabled() -> Vec<String> {
 
     names
 }
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn test_examples() {
+        use super::Version;
+        use crate::test_examples;
+        test_examples(Version {})
+    }
+}