Merge #10951

10951: feat: assist to generate documentation templates r=Veykril a=numero-744

Closes #10878, #1915 and #4767

Full description is in #10878, better read [the tests](https://github.com/rust-analyzer/rust-analyzer/pull/10951/files#diff-7a64e2efb66b2625443340fcbc96d531baff12c17cc0aaf51885ea94f67de254R424) to understand what this feature does.

- [x] There is one remaining thing about non-`pub` functions, what do you think about it?
- [x] In this PR [empty examples are generated](https://github.com/rust-analyzer/rust-analyzer/pull/10951/files#diff-7a64e2efb66b2625443340fcbc96d531baff12c17cc0aaf51885ea94f67de254R99) for `trait` functions, but maybe no examples should be provided at all.
- [x] If there is already a documentation, add another one with a separator ([currently done](https://github.com/rust-analyzer/rust-analyzer/pull/10951/files#diff-7a64e2efb66b2625443340fcbc96d531baff12c17cc0aaf51885ea94f67de254R74)) or simply disable this assist?
- [x] I will check once more that the generated examples are correct (ie. they are easy to fill before that they are built and tested)

Comments appreciated :smile: 

Co-authored-by: Côme ALLART <come.allart@etu.emse.fr>

3 files changed, 1123 insertions, 0 deletions

diff --git a/crates/ide_assists/src/handlers/generate_documentation_template.rs b/crates/ide_assists/src/handlers/generate_documentation_template.rs
new file mode 100644
index 00000000000..cfc7e9d0436
--- /dev/null
+++ b/crates/ide_assists/src/handlers/generate_documentation_template.rs
@@ -0,0 +1,1091 @@
+use hir::{AsAssocItem, HasVisibility, ModuleDef, Visibility};
+use ide_db::assists::{AssistId, AssistKind};
+use itertools::Itertools;
+use stdx::to_lower_snake_case;
+use syntax::{
+    ast::{self, edit::IndentLevel, HasDocComments, HasName},
+    AstNode,
+};
+
+use crate::assist_context::{AssistContext, Assists};
+
+// Assist: generate_documentation_template
+//
+// Adds a documentation template above a function definition / declaration.
+//
+// ```
+// pub fn my_$0func(a: i32, b: i32) -> Result<(), std::io::Error> {
+//     unimplemented!()
+// }
+// ```
+// ->
+// ```
+// /// .
+// ///
+// /// # Examples
+// ///
+// /// ```
+// /// use test::my_func;
+// ///
+// /// assert_eq!(my_func(a, b), );
+// /// ```
+// ///
+// /// # Errors
+// ///
+// /// This function will return an error if .
+// pub fn my_func(a: i32, b: i32) -> Result<(), std::io::Error> {
+//     unimplemented!()
+// }
+// ```
+pub(crate) fn generate_documentation_template(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+) -> Option<()> {
+    let name = ctx.find_node_at_offset::<ast::Name>()?;
+    let ast_func = name.syntax().parent().and_then(ast::Fn::cast)?;
+    if is_in_trait_impl(&ast_func, ctx)
+        || !is_public(&ast_func, ctx)?
+        || ast_func.doc_comments().next().is_some()
+    {
+        return None;
+    }
+
+    let parent_syntax = ast_func.syntax();
+    let text_range = parent_syntax.text_range();
+    let indent_level = IndentLevel::from_node(&parent_syntax);
+
+    acc.add(
+        AssistId("generate_documentation_template", AssistKind::Generate),
+        "Generate a documentation template",
+        text_range,
+        |builder| {
+            let mut doc_lines = Vec::new();
+            // Introduction / short function description before the sections
+            doc_lines.push(introduction_builder(&ast_func, ctx));
+            // Then come the sections
+            if let Some(mut lines) = examples_builder(&ast_func, ctx) {
+                doc_lines.push("".into());
+                doc_lines.append(&mut lines);
+            }
+            for section_builder in [panics_builder, errors_builder, safety_builder] {
+                if let Some(mut lines) = section_builder(&ast_func) {
+                    doc_lines.push("".into());
+                    doc_lines.append(&mut lines);
+                }
+            }
+            builder.insert(text_range.start(), documentation_from_lines(doc_lines, indent_level));
+        },
+    )
+}
+
+/// Builds an introduction, trying to be smart if the function is `::new()`
+fn introduction_builder(ast_func: &ast::Fn, ctx: &AssistContext) -> String {
+    || -> Option<String> {
+        let hir_func = ctx.sema.to_def(ast_func)?;
+        let container = hir_func.as_assoc_item(ctx.db())?.container(ctx.db());
+        if let hir::AssocItemContainer::Impl(implementation) = container {
+            let ret_ty = hir_func.ret_type(ctx.db());
+            let self_ty = implementation.self_ty(ctx.db());
+
+            let is_new = ast_func.name()?.to_string() == "new";
+            match is_new && ret_ty == self_ty {
+                true => Some(format!("Creates a new [`{}`].", self_type(ast_func)?)),
+                false => None,
+            }
+        } else {
+            None
+        }
+    }()
+    .unwrap_or_else(|| ".".into())
+}
+
+/// Builds an `# Examples` section. An option is returned to be able to manage an error in the AST.
+fn examples_builder(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<Vec<String>> {
+    let mut lines = string_vec_from(&["# Examples", "", "```"]);
+    if is_in_trait_def(ast_func, ctx) {
+        lines.push("// Example template not implemented for trait functions".into());
+    } else {
+        lines.append(&mut gen_ex_template(ast_func, ctx)?)
+    };
+
+    lines.push("```".into());
+    Some(lines)
+}
+
+/// Builds an optional `# Panics` section
+fn panics_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
+    match can_panic(ast_func) {
+        Some(true) => Some(string_vec_from(&["# Panics", "", "Panics if ."])),
+        _ => None,
+    }
+}
+
+/// Builds an optional `# Errors` section
+fn errors_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
+    match return_type(ast_func)?.to_string().contains("Result") {
+        true => Some(string_vec_from(&["# Errors", "", "This function will return an error if ."])),
+        false => None,
+    }
+}
+
+/// Builds an optional `# Safety` section
+fn safety_builder(ast_func: &ast::Fn) -> Option<Vec<String>> {
+    let is_unsafe = ast_func.unsafe_token().is_some();
+    match is_unsafe {
+        true => Some(string_vec_from(&["# Safety", "", "."])),
+        false => None,
+    }
+}
+
+/// Generates an example template
+fn gen_ex_template(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<Vec<String>> {
+    let mut lines = Vec::new();
+    let is_unsafe = ast_func.unsafe_token().is_some();
+    let param_list = ast_func.param_list()?;
+    let ref_mut_params = ref_mut_params(&param_list);
+    let self_name: Option<String> = self_name(ast_func);
+
+    lines.push(format!("use {};", build_path(ast_func, ctx)?));
+    lines.push("".into());
+    if let Some(self_definition) = self_definition(ast_func, self_name.as_deref()) {
+        lines.push(self_definition);
+    }
+    for param_name in &ref_mut_params {
+        lines.push(format!("let mut {} = ;", param_name))
+    }
+    // Call the function, check result
+    let function_call = function_call(ast_func, &param_list, self_name.as_deref(), is_unsafe)?;
+    if returns_a_value(ast_func, ctx) {
+        if count_parameters(&param_list) < 3 {
+            lines.push(format!("assert_eq!({}, );", function_call));
+        } else {
+            lines.push(format!("let result = {};", function_call));
+            lines.push("assert_eq!(result, );".into());
+        }
+    } else {
+        lines.push(format!("{};", function_call));
+    }
+    // Check the mutated values
+    if is_ref_mut_self(ast_func) == Some(true) {
+        lines.push(format!("assert_eq!({}, );", self_name?));
+    }
+    for param_name in &ref_mut_params {
+        lines.push(format!("assert_eq!({}, );", param_name));
+    }
+    Some(lines)
+}
+
+/// Checks if the function is public / exported
+fn is_public(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<bool> {
+    let hir_func = ctx.sema.to_def(ast_func)?;
+    Some(
+        hir_func.visibility(ctx.db()) == Visibility::Public
+            && all_parent_mods_public(&hir_func, ctx),
+    )
+}
+
+/// Checks that all parent modules of the function are public / exported
+fn all_parent_mods_public(hir_func: &hir::Function, ctx: &AssistContext) -> bool {
+    let mut module = hir_func.module(ctx.db());
+    loop {
+        if let Some(parent) = module.parent(ctx.db()) {
+            match ModuleDef::from(module).visibility(ctx.db()) {
+                Visibility::Public => module = parent,
+                _ => break false,
+            }
+        } else {
+            break true;
+        }
+    }
+}
+
+/// Returns the name of the current crate
+fn crate_name(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<String> {
+    let krate = ctx.sema.scope(&ast_func.syntax()).module()?.krate();
+    Some(krate.display_name(ctx.db())?.to_string())
+}
+
+/// `None` if function without a body; some bool to guess if function can panic
+fn can_panic(ast_func: &ast::Fn) -> Option<bool> {
+    let body = ast_func.body()?.to_string();
+    let can_panic = body.contains("panic!(")
+        // FIXME it would be better to not match `debug_assert*!` macro invocations
+        || body.contains("assert!(")
+        || body.contains(".unwrap()")
+        || body.contains(".expect(");
+    Some(can_panic)
+}
+
+/// Helper function to get the name that should be given to `self` arguments
+fn self_name(ast_func: &ast::Fn) -> Option<String> {
+    self_partial_type(ast_func).map(|name| to_lower_snake_case(&name))
+}
+
+/// Heper function to get the name of the type of `self`
+fn self_type(ast_func: &ast::Fn) -> Option<String> {
+    ast_func
+        .syntax()
+        .ancestors()
+        .find_map(ast::Impl::cast)
+        .and_then(|i| i.self_ty())
+        .map(|t| (t.to_string()))
+}
+
+/// Heper function to get the name of the type of `self` without generic arguments
+fn self_partial_type(ast_func: &ast::Fn) -> Option<String> {
+    let mut self_type = self_type(ast_func)?;
+    if let Some(idx) = self_type.find(|c| ['<', ' '].contains(&c)) {
+        self_type.truncate(idx);
+    }
+    Some(self_type)
+}
+
+/// Helper function to determine if the function is in a trait implementation
+fn is_in_trait_impl(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
+    ctx.sema
+        .to_def(ast_func)
+        .and_then(|hir_func| hir_func.as_assoc_item(ctx.db()))
+        .and_then(|assoc_item| assoc_item.containing_trait_impl(ctx.db()))
+        .is_some()
+}
+
+/// Helper function to determine if the function definition is in a trait definition
+fn is_in_trait_def(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
+    ctx.sema
+        .to_def(ast_func)
+        .and_then(|hir_func| hir_func.as_assoc_item(ctx.db()))
+        .and_then(|assoc_item| assoc_item.containing_trait(ctx.db()))
+        .is_some()
+}
+
+/// Returns `None` if no `self` at all, `Some(true)` if there is `&mut self` else `Some(false)`
+fn is_ref_mut_self(ast_func: &ast::Fn) -> Option<bool> {
+    let self_param = ast_func.param_list()?.self_param()?;
+    Some(self_param.mut_token().is_some() && self_param.amp_token().is_some())
+}
+
+/// Helper function to define an variable to be the `self` argument
+fn self_definition(ast_func: &ast::Fn, self_name: Option<&str>) -> Option<String> {
+    let definition = match is_ref_mut_self(ast_func)? {
+        true => format!("let mut {} = ;", self_name?),
+        false => format!("let {} = ;", self_name?),
+    };
+    Some(definition)
+}
+
+/// Helper function to determine if a parameter is `&mut`
+fn is_a_ref_mut_param(param: &ast::Param) -> bool {
+    match param.ty() {
+        Some(ast::Type::RefType(param_ref)) => param_ref.mut_token().is_some(),
+        _ => false,
+    }
+}
+
+/// Helper function to build the list of `&mut` parameters
+fn ref_mut_params(param_list: &ast::ParamList) -> Vec<String> {
+    param_list
+        .params()
+        .filter_map(|param| match is_a_ref_mut_param(&param) {
+            // Maybe better filter the param name (to do this maybe extract a function from
+            // `arguments_from_params`?) in case of a `mut a: &mut T`. Anyway managing most (not
+            // all) cases might be enough, the goal is just to produce a template.
+            true => Some(param.pat()?.to_string()),
+            false => None,
+        })
+        .collect()
+}
+
+/// Helper function to build the comma-separated list of arguments of the function
+fn arguments_from_params(param_list: &ast::ParamList) -> String {
+    let args_iter = param_list.params().map(|param| match param.pat() {
+        // To avoid `mut` in the function call (which would be a nonsense), `Pat` should not be
+        // written as is so its variants must be managed independently. Other variants (for
+        // instance `TuplePat`) could be managed later.
+        Some(ast::Pat::IdentPat(ident_pat)) => match ident_pat.name() {
+            Some(name) => match is_a_ref_mut_param(&param) {
+                true => format!("&mut {}", name.to_string()),
+                false => name.to_string(),
+            },
+            None => "_".to_string(),
+        },
+        _ => "_".to_string(),
+    });
+    Itertools::intersperse(args_iter, ", ".to_string()).collect()
+}
+
+/// Helper function to build a function call. `None` if expected `self_name` was not provided
+fn function_call(
+    ast_func: &ast::Fn,
+    param_list: &ast::ParamList,
+    self_name: Option<&str>,
+    is_unsafe: bool,
+) -> Option<String> {
+    let name = ast_func.name()?;
+    let arguments = arguments_from_params(&param_list);
+    let function_call = if param_list.self_param().is_some() {
+        format!("{}.{}({})", self_name?, name, arguments)
+    } else if let Some(implementation) = self_partial_type(ast_func) {
+        format!("{}::{}({})", implementation, name, arguments)
+    } else {
+        format!("{}({})", name, arguments)
+    };
+    match is_unsafe {
+        true => Some(format!("unsafe {{ {} }}", function_call)),
+        false => Some(function_call),
+    }
+}
+
+/// Helper function to count the parameters including `self`
+fn count_parameters(param_list: &ast::ParamList) -> usize {
+    param_list.params().count() + if param_list.self_param().is_some() { 1 } else { 0 }
+}
+
+/// Helper function to transform lines of documentation into a Rust code documentation
+fn documentation_from_lines(doc_lines: Vec<String>, indent_level: IndentLevel) -> String {
+    let mut result = String::new();
+    for doc_line in doc_lines {
+        result.push_str("///");
+        if !doc_line.is_empty() {
+            result.push(' ');
+            result.push_str(&doc_line);
+        }
+        result.push('\n');
+        result.push_str(&indent_level.to_string());
+    }
+    result
+}
+
+/// Helper function to transform an array of borrowed strings to an owned `Vec<String>`
+fn string_vec_from(string_array: &[&str]) -> Vec<String> {
+    string_array.iter().map(|&s| s.to_owned()).collect()
+}
+
+/// Helper function to build the path of the module in the which is the node
+fn build_path(ast_func: &ast::Fn, ctx: &AssistContext) -> Option<String> {
+    let crate_name = crate_name(ast_func, ctx)?;
+    let leaf = self_partial_type(ast_func)
+        .or_else(|| ast_func.name().map(|n| n.to_string()))
+        .unwrap_or_else(|| "*".into());
+    let module_def: ModuleDef = ctx.sema.to_def(ast_func)?.module(ctx.db()).into();
+    match module_def.canonical_path(ctx.db()) {
+        Some(path) => Some(format!("{}::{}::{}", crate_name, path, leaf)),
+        None => Some(format!("{}::{}", crate_name, leaf)),
+    }
+}
+
+/// Helper function to get the return type of a function
+fn return_type(ast_func: &ast::Fn) -> Option<ast::Type> {
+    ast_func.ret_type()?.ty()
+}
+
+/// Helper function to determine if the function returns some data
+fn returns_a_value(ast_func: &ast::Fn, ctx: &AssistContext) -> bool {
+    ctx.sema
+        .to_def(ast_func)
+        .map(|hir_func| hir_func.ret_type(ctx.db()))
+        .map(|ret_ty| !ret_ty.is_unit() && !ret_ty.is_never())
+        .unwrap_or(false)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn not_applicable_on_function_calls() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+fn hello_world() {}
+fn calls_hello_world() {
+    hello_world$0();
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn not_applicable_in_trait_impl() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+trait MyTrait {}
+struct MyStruct;
+impl MyTrait for MyStruct {
+    fn hello_world$0();
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn not_applicable_if_function_is_private() {
+        check_assist_not_applicable(generate_documentation_template, r#"fn priv$0ate() {}"#);
+    }
+
+    #[test]
+    fn not_applicable_if_function_is_pub_crate() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"pub(crate) fn pri$0vate() {}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_if_function_is_in_private_mod() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+mod PrivateModule {
+    pub fn pri$0vate() {}
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_if_function_is_in_pub_crate_mod() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+pub(crate) mod PrivateModule {
+    pub fn pr$0ivate() {}
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_if_function_is_in_non_public_mod_is_recursive() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+mod ParentPrivateModule {
+    pub mod PrivateModule {
+        pub fn pr$0ivate() {}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_if_function_already_documented() {
+        check_assist_not_applicable(
+            generate_documentation_template,
+            r#"
+/// Some documentation here
+pub fn $0documented_function() {}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_noop_function() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn no$0op() {}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::noop;
+///
+/// noop();
+/// ```
+pub fn noop() {}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_a_parameter() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn no$0op_with_param(_a: i32) {}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::noop_with_param;
+///
+/// noop_with_param(_a);
+/// ```
+pub fn noop_with_param(_a: i32) {}
+"#,
+        );
+    }
+
+    #[test]
+    fn detects_unsafe_function() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub unsafe fn no$0op_unsafe() {}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::noop_unsafe;
+///
+/// unsafe { noop_unsafe() };
+/// ```
+///
+/// # Safety
+///
+/// .
+pub unsafe fn noop_unsafe() {}
+"#,
+        );
+    }
+
+    #[test]
+    fn guesses_panic_macro_can_panic() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn panic$0s_if(a: bool) {
+    if a {
+        panic!();
+    }
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::panics_if;
+///
+/// panics_if(a);
+/// ```
+///
+/// # Panics
+///
+/// Panics if .
+pub fn panics_if(a: bool) {
+    if a {
+        panic!();
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn guesses_assert_macro_can_panic() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn $0panics_if_not(a: bool) {
+    assert!(a == true);
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::panics_if_not;
+///
+/// panics_if_not(a);
+/// ```
+///
+/// # Panics
+///
+/// Panics if .
+pub fn panics_if_not(a: bool) {
+    assert!(a == true);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn guesses_unwrap_can_panic() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn $0panics_if_none(a: Option<()>) {
+    a.unwrap();
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::panics_if_none;
+///
+/// panics_if_none(a);
+/// ```
+///
+/// # Panics
+///
+/// Panics if .
+pub fn panics_if_none(a: Option<()>) {
+    a.unwrap();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn guesses_expect_can_panic() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn $0panics_if_none2(a: Option<()>) {
+    a.expect("Bouh!");
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::panics_if_none2;
+///
+/// panics_if_none2(a);
+/// ```
+///
+/// # Panics
+///
+/// Panics if .
+pub fn panics_if_none2(a: Option<()>) {
+    a.expect("Bouh!");
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn checks_output_in_example() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn returns_a_value$0() -> i32 {
+    0
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::returns_a_value;
+///
+/// assert_eq!(returns_a_value(), );
+/// ```
+pub fn returns_a_value() -> i32 {
+    0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn detects_result_output() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn returns_a_result$0() -> Result<i32, std::io::Error> {
+    Ok(0)
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::returns_a_result;
+///
+/// assert_eq!(returns_a_result(), );
+/// ```
+///
+/// # Errors
+///
+/// This function will return an error if .
+pub fn returns_a_result() -> Result<i32, std::io::Error> {
+    Ok(0)
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn checks_ref_mut_in_example() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn modifies_a_value$0(a: &mut i32) {
+    *a = 0;
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::modifies_a_value;
+///
+/// let mut a = ;
+/// modifies_a_value(&mut a);
+/// assert_eq!(a, );
+/// ```
+pub fn modifies_a_value(a: &mut i32) {
+    *a = 0;
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn stores_result_if_at_least_3_params() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub fn sum3$0(a: i32, b: i32, c: i32) -> i32 {
+    a + b + c
+}
+"#,
+            r#"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::sum3;
+///
+/// let result = sum3(a, b, c);
+/// assert_eq!(result, );
+/// ```
+pub fn sum3(a: i32, b: i32, c: i32) -> i32 {
+    a + b + c
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_fn_in_mods() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub mod a {
+    pub mod b {
+        pub fn no$0op() {}
+    }
+}
+"#,
+            r#"
+pub mod a {
+    pub mod b {
+        /// .
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use test::a::b::noop;
+        ///
+        /// noop();
+        /// ```
+        pub fn noop() {}
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_fn_in_impl() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub struct MyStruct;
+impl MyStruct {
+    pub fn no$0op() {}
+}
+"#,
+            r#"
+pub struct MyStruct;
+impl MyStruct {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use test::MyStruct;
+    ///
+    /// MyStruct::noop();
+    /// ```
+    pub fn noop() {}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_fn_in_trait() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub trait MyTrait {
+    fn fun$0ction_trait();
+}
+"#,
+            r#"
+pub trait MyTrait {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // Example template not implemented for trait functions
+    /// ```
+    fn function_trait();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_unsafe_fn_in_trait() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub trait MyTrait {
+    unsafe fn unsafe_funct$0ion_trait();
+}
+"#,
+            r#"
+pub trait MyTrait {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // Example template not implemented for trait functions
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// .
+    unsafe fn unsafe_function_trait();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_fn_in_trait_with_default_panicking() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub trait MyTrait {
+    fn function_trait_with_$0default_panicking() {
+        panic!()
+    }
+}
+"#,
+            r#"
+pub trait MyTrait {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // Example template not implemented for trait functions
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if .
+    fn function_trait_with_default_panicking() {
+        panic!()
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_fn_in_trait_returning_result() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+pub trait MyTrait {
+    fn function_tr$0ait_returning_result() -> Result<(), std::io::Error>;
+}
+"#,
+            r#"
+pub trait MyTrait {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// // Example template not implemented for trait functions
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if .
+    fn function_trait_returning_result() -> Result<(), std::io::Error>;
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn detects_new() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+#[derive(Debug, PartialEq)]
+pub struct MyGenericStruct<T> {
+    pub x: T,
+}
+impl<T> MyGenericStruct<T> {
+    pub fn new$0(x: T) -> MyGenericStruct<T> {
+        MyGenericStruct { x }
+    }
+}
+"#,
+            r#"
+#[derive(Debug, PartialEq)]
+pub struct MyGenericStruct<T> {
+    pub x: T,
+}
+impl<T> MyGenericStruct<T> {
+    /// Creates a new [`MyGenericStruct<T>`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use test::MyGenericStruct;
+    ///
+    /// assert_eq!(MyGenericStruct::new(x), );
+    /// ```
+    pub fn new(x: T) -> MyGenericStruct<T> {
+        MyGenericStruct { x }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn detects_new_with_self() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+#[derive(Debug, PartialEq)]
+pub struct MyGenericStruct2<T> {
+    pub x: T,
+}
+impl<T> MyGenericStruct2<T> {
+    pub fn new$0(x: T) -> Self {
+        MyGenericStruct2 { x }
+    }
+}
+"#,
+            r#"
+#[derive(Debug, PartialEq)]
+pub struct MyGenericStruct2<T> {
+    pub x: T,
+}
+impl<T> MyGenericStruct2<T> {
+    /// Creates a new [`MyGenericStruct2<T>`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use test::MyGenericStruct2;
+    ///
+    /// assert_eq!(MyGenericStruct2::new(x), );
+    /// ```
+    pub fn new(x: T) -> Self {
+        MyGenericStruct2 { x }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn supports_method_call() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+impl<T> MyGenericStruct<T> {
+    pub fn co$0nsume(self) {}
+}
+"#,
+            r#"
+impl<T> MyGenericStruct<T> {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use test::MyGenericStruct;
+    ///
+    /// let my_generic_struct = ;
+    /// my_generic_struct.consume();
+    /// ```
+    pub fn consume(self) {}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn checks_modified_self_param() {
+        check_assist(
+            generate_documentation_template,
+            r#"
+impl<T> MyGenericStruct<T> {
+    pub fn modi$0fy(&mut self, new_value: T) {
+        self.x = new_value;
+    }
+}
+"#,
+            r#"
+impl<T> MyGenericStruct<T> {
+    /// .
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use test::MyGenericStruct;
+    ///
+    /// let mut my_generic_struct = ;
+    /// my_generic_struct.modify(new_value);
+    /// assert_eq!(my_generic_struct, );
+    /// ```
+    pub fn modify(&mut self, new_value: T) {
+        self.x = new_value;
+    }
+}
+"#,
+        );
+    }
+}
diff --git a/crates/ide_assists/src/lib.rs b/crates/ide_assists/src/lib.rs
index 5d4c1532dbe..61ac45637be 100644
--- a/crates/ide_assists/src/lib.rs
+++ b/crates/ide_assists/src/lib.rs
@@ -136,6 +136,7 @@ mod handlers {
     mod generate_default_from_new;
     mod generate_deref;
     mod generate_derive;
+    mod generate_documentation_template;
     mod generate_enum_is_method;
     mod generate_enum_projection_method;
     mod generate_from_impl_for_enum;
@@ -219,6 +220,7 @@ mod handlers {
             generate_delegate_methods::generate_delegate_methods,
             generate_deref::generate_deref,
             generate_derive::generate_derive,
+            generate_documentation_template::generate_documentation_template,
             generate_enum_is_method::generate_enum_is_method,
             generate_enum_projection_method::generate_enum_as_method,
             generate_enum_projection_method::generate_enum_try_into_method,
diff --git a/crates/ide_assists/src/tests/generated.rs b/crates/ide_assists/src/tests/generated.rs
index e30f98bcd13..c67e15b2ce4 100644
--- a/crates/ide_assists/src/tests/generated.rs
+++ b/crates/ide_assists/src/tests/generated.rs
@@ -840,6 +840,36 @@ struct Point {
 }
 
 #[test]
+fn doctest_generate_documentation_template() {
+    check_doc_test(
+        "generate_documentation_template",
+        r#####"
+pub fn my_$0func(a: i32, b: i32) -> Result<(), std::io::Error> {
+    unimplemented!()
+}
+"#####,
+        r#####"
+/// .
+///
+/// # Examples
+///
+/// ```
+/// use test::my_func;
+///
+/// assert_eq!(my_func(a, b), );
+/// ```
+///
+/// # Errors
+///
+/// This function will return an error if .
+pub fn my_func(a: i32, b: i32) -> Result<(), std::io::Error> {
+    unimplemented!()
+}
+"#####,
+    )
+}
+
+#[test]
 fn doctest_generate_enum_as_method() {
     check_doc_test(
         "generate_enum_as_method",