1 files changed, 927 insertions, 0 deletions

diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
new file mode 100644
index 000000000..002adf915
--- /dev/null
+++ b/crates/ide/src/inlay_hints.rs
@@ -0,0 +1,927 @@
+use hir::{Adt, Callable, HirDisplay, Semantics, Type};
+use ide_db::RootDatabase;
+use stdx::to_lower_snake_case;
+use syntax::{
+    ast::{self, ArgListOwner, AstNode},
+    match_ast, Direction, NodeOrToken, SmolStr, SyntaxKind, TextRange, T,
+};
+
+use crate::FileId;
+use ast::NameOwner;
+use either::Either;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct InlayHintsConfig {
+    pub type_hints: bool,
+    pub parameter_hints: bool,
+    pub chaining_hints: bool,
+    pub max_length: Option<usize>,
+}
+
+impl Default for InlayHintsConfig {
+    fn default() -> Self {
+        Self { type_hints: true, parameter_hints: true, chaining_hints: true, max_length: None }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum InlayKind {
+    TypeHint,
+    ParameterHint,
+    ChainingHint,
+}
+
+#[derive(Debug)]
+pub struct InlayHint {
+    pub range: TextRange,
+    pub kind: InlayKind,
+    pub label: SmolStr,
+}
+
+// Feature: Inlay Hints
+//
+// rust-analyzer shows additional information inline with the source code.
+// Editors usually render this using read-only virtual text snippets interspersed with code.
+//
+// rust-analyzer shows hits for
+//
+// * types of local variables
+// * names of function arguments
+// * types of chained expressions
+//
+// **Note:** VS Code does not have native support for inlay hints https://github.com/microsoft/vscode/issues/16221[yet] and the hints are implemented using decorations.
+// This approach has limitations, the caret movement and bracket highlighting near the edges of the hint may be weird:
+// https://github.com/rust-analyzer/rust-analyzer/issues/1623[1], https://github.com/rust-analyzer/rust-analyzer/issues/3453[2].
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Toggle inlay hints*
+// |===
+pub(crate) fn inlay_hints(
+    db: &RootDatabase,
+    file_id: FileId,
+    config: &InlayHintsConfig,
+) -> Vec<InlayHint> {
+    let _p = profile::span("inlay_hints");
+    let sema = Semantics::new(db);
+    let file = sema.parse(file_id);
+
+    let mut res = Vec::new();
+    for node in file.syntax().descendants() {
+        if let Some(expr) = ast::Expr::cast(node.clone()) {
+            get_chaining_hints(&mut res, &sema, config, expr);
+        }
+
+        match_ast! {
+            match node {
+                ast::CallExpr(it) => { get_param_name_hints(&mut res, &sema, config, ast::Expr::from(it)); },
+                ast::MethodCallExpr(it) => { get_param_name_hints(&mut res, &sema, config, ast::Expr::from(it)); },
+                ast::IdentPat(it) => { get_bind_pat_hints(&mut res, &sema, config, it); },
+                _ => (),
+            }
+        }
+    }
+    res
+}
+
+fn get_chaining_hints(
+    acc: &mut Vec<InlayHint>,
+    sema: &Semantics<RootDatabase>,
+    config: &InlayHintsConfig,
+    expr: ast::Expr,
+) -> Option<()> {
+    if !config.chaining_hints {
+        return None;
+    }
+
+    if matches!(expr, ast::Expr::RecordExpr(_)) {
+        return None;
+    }
+
+    let mut tokens = expr
+        .syntax()
+        .siblings_with_tokens(Direction::Next)
+        .filter_map(NodeOrToken::into_token)
+        .filter(|t| match t.kind() {
+            SyntaxKind::WHITESPACE if !t.text().contains('\n') => false,
+            SyntaxKind::COMMENT => false,
+            _ => true,
+        });
+
+    // Chaining can be defined as an expression whose next sibling tokens are newline and dot
+    // Ignoring extra whitespace and comments
+    let next = tokens.next()?.kind();
+    let next_next = tokens.next()?.kind();
+    if next == SyntaxKind::WHITESPACE && next_next == T![.] {
+        let ty = sema.type_of_expr(&expr)?;
+        if ty.is_unknown() {
+            return None;
+        }
+        if matches!(expr, ast::Expr::PathExpr(_)) {
+            if let Some(Adt::Struct(st)) = ty.as_adt() {
+                if st.fields(sema.db).is_empty() {
+                    return None;
+                }
+            }
+        }
+        let label = ty.display_truncated(sema.db, config.max_length).to_string();
+        acc.push(InlayHint {
+            range: expr.syntax().text_range(),
+            kind: InlayKind::ChainingHint,
+            label: label.into(),
+        });
+    }
+    Some(())
+}
+
+fn get_param_name_hints(
+    acc: &mut Vec<InlayHint>,
+    sema: &Semantics<RootDatabase>,
+    config: &InlayHintsConfig,
+    expr: ast::Expr,
+) -> Option<()> {
+    if !config.parameter_hints {
+        return None;
+    }
+
+    let args = match &expr {
+        ast::Expr::CallExpr(expr) => expr.arg_list()?.args(),
+        ast::Expr::MethodCallExpr(expr) => expr.arg_list()?.args(),
+        _ => return None,
+    };
+
+    let callable = get_callable(sema, &expr)?;
+    let hints = callable
+        .params(sema.db)
+        .into_iter()
+        .zip(args)
+        .filter_map(|((param, _ty), arg)| {
+            let param_name = match param? {
+                Either::Left(self_param) => self_param.to_string(),
+                Either::Right(pat) => match pat {
+                    ast::Pat::IdentPat(it) => it.name()?.to_string(),
+                    _ => return None,
+                },
+            };
+            Some((param_name, arg))
+        })
+        .filter(|(param_name, arg)| should_show_param_name_hint(sema, &callable, &param_name, &arg))
+        .map(|(param_name, arg)| InlayHint {
+            range: arg.syntax().text_range(),
+            kind: InlayKind::ParameterHint,
+            label: param_name.into(),
+        });
+
+    acc.extend(hints);
+    Some(())
+}
+
+fn get_bind_pat_hints(
+    acc: &mut Vec<InlayHint>,
+    sema: &Semantics<RootDatabase>,
+    config: &InlayHintsConfig,
+    pat: ast::IdentPat,
+) -> Option<()> {
+    if !config.type_hints {
+        return None;
+    }
+
+    let ty = sema.type_of_pat(&pat.clone().into())?;
+
+    if should_not_display_type_hint(sema.db, &pat, &ty) {
+        return None;
+    }
+
+    acc.push(InlayHint {
+        range: pat.syntax().text_range(),
+        kind: InlayKind::TypeHint,
+        label: ty.display_truncated(sema.db, config.max_length).to_string().into(),
+    });
+    Some(())
+}
+
+fn pat_is_enum_variant(db: &RootDatabase, bind_pat: &ast::IdentPat, pat_ty: &Type) -> bool {
+    if let Some(Adt::Enum(enum_data)) = pat_ty.as_adt() {
+        let pat_text = bind_pat.to_string();
+        enum_data
+            .variants(db)
+            .into_iter()
+            .map(|variant| variant.name(db).to_string())
+            .any(|enum_name| enum_name == pat_text)
+    } else {
+        false
+    }
+}
+
+fn should_not_display_type_hint(
+    db: &RootDatabase,
+    bind_pat: &ast::IdentPat,
+    pat_ty: &Type,
+) -> bool {
+    if pat_ty.is_unknown() {
+        return true;
+    }
+
+    if let Some(Adt::Struct(s)) = pat_ty.as_adt() {
+        if s.fields(db).is_empty() && s.name(db).to_string() == bind_pat.to_string() {
+            return true;
+        }
+    }
+
+    for node in bind_pat.syntax().ancestors() {
+        match_ast! {
+            match node {
+                ast::LetStmt(it) => {
+                    return it.ty().is_some()
+                },
+                ast::Param(it) => {
+                    return it.ty().is_some()
+                },
+                ast::MatchArm(_it) => {
+                    return pat_is_enum_variant(db, bind_pat, pat_ty);
+                },
+                ast::IfExpr(it) => {
+                    return it.condition().and_then(|condition| condition.pat()).is_some()
+                        && pat_is_enum_variant(db, bind_pat, pat_ty);
+                },
+                ast::WhileExpr(it) => {
+                    return it.condition().and_then(|condition| condition.pat()).is_some()
+                        && pat_is_enum_variant(db, bind_pat, pat_ty);
+                },
+                _ => (),
+            }
+        }
+    }
+    false
+}
+
+fn should_show_param_name_hint(
+    sema: &Semantics<RootDatabase>,
+    callable: &Callable,
+    param_name: &str,
+    argument: &ast::Expr,
+) -> bool {
+    let param_name = param_name.trim_start_matches('_');
+    let fn_name = match callable.kind() {
+        hir::CallableKind::Function(it) => Some(it.name(sema.db).to_string()),
+        hir::CallableKind::TupleStruct(_)
+        | hir::CallableKind::TupleEnumVariant(_)
+        | hir::CallableKind::Closure => None,
+    };
+    if param_name.is_empty()
+        || Some(param_name) == fn_name.as_ref().map(|s| s.trim_start_matches('_'))
+        || is_argument_similar_to_param_name(sema, argument, param_name)
+        || param_name.starts_with("ra_fixture")
+    {
+        return false;
+    }
+
+    // avoid displaying hints for common functions like map, filter, etc.
+    // or other obvious words used in std
+    !(callable.n_params() == 1 && is_obvious_param(param_name))
+}
+
+fn is_argument_similar_to_param_name(
+    sema: &Semantics<RootDatabase>,
+    argument: &ast::Expr,
+    param_name: &str,
+) -> bool {
+    if is_enum_name_similar_to_param_name(sema, argument, param_name) {
+        return true;
+    }
+    match get_string_representation(argument) {
+        None => false,
+        Some(repr) => {
+            let argument_string = repr.trim_start_matches('_');
+            argument_string.starts_with(param_name) || argument_string.ends_with(param_name)
+        }
+    }
+}
+
+fn is_enum_name_similar_to_param_name(
+    sema: &Semantics<RootDatabase>,
+    argument: &ast::Expr,
+    param_name: &str,
+) -> bool {
+    match sema.type_of_expr(argument).and_then(|t| t.as_adt()) {
+        Some(Adt::Enum(e)) => to_lower_snake_case(&e.name(sema.db).to_string()) == param_name,
+        _ => false,
+    }
+}
+
+fn get_string_representation(expr: &ast::Expr) -> Option<String> {
+    match expr {
+        ast::Expr::MethodCallExpr(method_call_expr) => {
+            Some(method_call_expr.name_ref()?.to_string())
+        }
+        ast::Expr::RefExpr(ref_expr) => get_string_representation(&ref_expr.expr()?),
+        _ => Some(expr.to_string()),
+    }
+}
+
+fn is_obvious_param(param_name: &str) -> bool {
+    let is_obvious_param_name =
+        matches!(param_name, "predicate" | "value" | "pat" | "rhs" | "other");
+    param_name.len() == 1 || is_obvious_param_name
+}
+
+fn get_callable(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<Callable> {
+    match expr {
+        ast::Expr::CallExpr(expr) => sema.type_of_expr(&expr.expr()?)?.as_callable(sema.db),
+        ast::Expr::MethodCallExpr(expr) => sema.resolve_method_call_as_callable(expr),
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use expect::{expect, Expect};
+    use test_utils::extract_annotations;
+
+    use crate::{inlay_hints::InlayHintsConfig, mock_analysis::single_file};
+
+    fn check(ra_fixture: &str) {
+        check_with_config(InlayHintsConfig::default(), ra_fixture);
+    }
+
+    fn check_with_config(config: InlayHintsConfig, ra_fixture: &str) {
+        let (analysis, file_id) = single_file(ra_fixture);
+        let expected = extract_annotations(&*analysis.file_text(file_id).unwrap());
+        let inlay_hints = analysis.inlay_hints(file_id, &config).unwrap();
+        let actual =
+            inlay_hints.into_iter().map(|it| (it.range, it.label.to_string())).collect::<Vec<_>>();
+        assert_eq!(expected, actual, "\nExpected:\n{:#?}\n\nActual:\n{:#?}", expected, actual);
+    }
+
+    fn check_expect(config: InlayHintsConfig, ra_fixture: &str, expect: Expect) {
+        let (analysis, file_id) = single_file(ra_fixture);
+        let inlay_hints = analysis.inlay_hints(file_id, &config).unwrap();
+        expect.assert_debug_eq(&inlay_hints)
+    }
+
+    #[test]
+    fn param_hints_only() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: true,
+                type_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn foo(a: i32, b: i32) -> i32 { a + b }
+fn main() {
+    let _x = foo(
+        4,
+      //^ a
+        4,
+      //^ b
+    );
+}"#,
+        );
+    }
+
+    #[test]
+    fn hints_disabled() {
+        check_with_config(
+            InlayHintsConfig {
+                type_hints: false,
+                parameter_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn foo(a: i32, b: i32) -> i32 { a + b }
+fn main() {
+    let _x = foo(4, 4);
+}"#,
+        );
+    }
+
+    #[test]
+    fn type_hints_only() {
+        check_with_config(
+            InlayHintsConfig {
+                type_hints: true,
+                parameter_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn foo(a: i32, b: i32) -> i32 { a + b }
+fn main() {
+    let _x = foo(4, 4);
+      //^^ i32
+}"#,
+        );
+    }
+
+    #[test]
+    fn default_generic_types_should_not_be_displayed() {
+        check(
+            r#"
+struct Test<K, T = u8> { k: K, t: T }
+
+fn main() {
+    let zz = Test { t: 23u8, k: 33 };
+      //^^ Test<i32>
+    let zz_ref = &zz;
+      //^^^^^^ &Test<i32>
+    let test = || zz;
+      //^^^^ || -> Test<i32>
+}"#,
+        );
+    }
+
+    #[test]
+    fn let_statement() {
+        check(
+            r#"
+#[derive(PartialEq)]
+enum Option<T> { None, Some(T) }
+
+#[derive(PartialEq)]
+struct Test { a: Option<u32>, b: u8 }
+
+fn main() {
+    struct InnerStruct {}
+
+    let test = 54;
+      //^^^^ i32
+    let test: i32 = 33;
+    let mut test = 33;
+      //^^^^^^^^ i32
+    let _ = 22;
+    let test = "test";
+      //^^^^ &str
+    let test = InnerStruct {};
+
+    let test = unresolved();
+
+    let test = (42, 'a');
+      //^^^^ (i32, char)
+    let (a,    (b,     (c,)) = (2, (3, (9.2,));
+       //^ i32  ^ i32   ^ f64
+    let &x = &92;
+       //^ i32
+}"#,
+        );
+    }
+
+    #[test]
+    fn closure_parameters() {
+        check(
+            r#"
+fn main() {
+    let mut start = 0;
+      //^^^^^^^^^ i32
+    (0..2).for_each(|increment| { start += increment; });
+                   //^^^^^^^^^ i32
+
+    let multiply =
+      //^^^^^^^^ |…| -> i32
+      | a,     b| a * b
+      //^ i32  ^ i32
+    ;
+
+    let _: i32 = multiply(1, 2);
+    let multiply_ref = &multiply;
+      //^^^^^^^^^^^^ &|…| -> i32
+
+    let return_42 = || 42;
+      //^^^^^^^^^ || -> i32
+}"#,
+        );
+    }
+
+    #[test]
+    fn for_expression() {
+        check(
+            r#"
+fn main() {
+    let mut start = 0;
+      //^^^^^^^^^ i32
+    for increment in 0..2 { start += increment; }
+      //^^^^^^^^^ i32
+}"#,
+        );
+    }
+
+    #[test]
+    fn if_expr() {
+        check(
+            r#"
+enum Option<T> { None, Some(T) }
+use Option::*;
+
+struct Test { a: Option<u32>, b: u8 }
+
+fn main() {
+    let test = Some(Test { a: Some(3), b: 1 });
+      //^^^^ Option<Test>
+    if let None = &test {};
+    if let test = &test {};
+         //^^^^ &Option<Test>
+    if let Some(test) = &test {};
+              //^^^^ &Test
+    if let Some(Test { a,             b }) = &test {};
+                     //^ &Option<u32> ^ &u8
+    if let Some(Test { a: x,             b: y }) = &test {};
+                        //^ &Option<u32>    ^ &u8
+    if let Some(Test { a: Some(x),  b: y }) = &test {};
+                             //^ &u32  ^ &u8
+    if let Some(Test { a: None,  b: y }) = &test {};
+                                  //^ &u8
+    if let Some(Test { b: y, .. }) = &test {};
+                        //^ &u8
+    if test == None {}
+}"#,
+        );
+    }
+
+    #[test]
+    fn while_expr() {
+        check(
+            r#"
+enum Option<T> { None, Some(T) }
+use Option::*;
+
+struct Test { a: Option<u32>, b: u8 }
+
+fn main() {
+    let test = Some(Test { a: Some(3), b: 1 });
+      //^^^^ Option<Test>
+    while let Some(Test { a: Some(x),  b: y }) = &test {};
+                                //^ &u32  ^ &u8
+}"#,
+        );
+    }
+
+    #[test]
+    fn match_arm_list() {
+        check(
+            r#"
+enum Option<T> { None, Some(T) }
+use Option::*;
+
+struct Test { a: Option<u32>, b: u8 }
+
+fn main() {
+    match Some(Test { a: Some(3), b: 1 }) {
+        None => (),
+        test => (),
+      //^^^^ Option<Test>
+        Some(Test { a: Some(x), b: y }) => (),
+                          //^ u32  ^ u8
+        _ => {}
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn hint_truncation() {
+        check_with_config(
+            InlayHintsConfig { max_length: Some(8), ..Default::default() },
+            r#"
+struct Smol<T>(T);
+
+struct VeryLongOuterName<T>(T);
+
+fn main() {
+    let a = Smol(0u32);
+      //^ Smol<u32>
+    let b = VeryLongOuterName(0usize);
+      //^ VeryLongOuterName<…>
+    let c = Smol(Smol(0u32))
+      //^ Smol<Smol<…>>
+}"#,
+        );
+    }
+
+    #[test]
+    fn function_call_parameter_hint() {
+        check(
+            r#"
+enum Option<T> { None, Some(T) }
+use Option::*;
+
+struct FileId {}
+struct SmolStr {}
+
+struct TextRange {}
+struct SyntaxKind {}
+struct NavigationTarget {}
+
+struct Test {}
+
+impl Test {
+    fn method(&self, mut param: i32) -> i32 { param * 2 }
+
+    fn from_syntax(
+        file_id: FileId,
+        name: SmolStr,
+        focus_range: Option<TextRange>,
+        full_range: TextRange,
+        kind: SyntaxKind,
+        docs: Option<String>,
+    ) -> NavigationTarget {
+        NavigationTarget {}
+    }
+}
+
+fn test_func(mut foo: i32, bar: i32, msg: &str, _: i32, last: i32) -> i32 {
+    foo + bar
+}
+
+fn main() {
+    let not_literal = 1;
+      //^^^^^^^^^^^ i32
+    let _: i32 = test_func(1,    2,      "hello", 3,  not_literal);
+                         //^ foo ^ bar   ^^^^^^^ msg  ^^^^^^^^^^^ last
+    let t: Test = Test {};
+    t.method(123);
+           //^^^ param
+    Test::method(&t,      3456);
+               //^^ &self ^^^^ param
+    Test::from_syntax(
+        FileId {},
+      //^^^^^^^^^ file_id
+        "impl".into(),
+      //^^^^^^^^^^^^^ name
+        None,
+      //^^^^ focus_range
+        TextRange {},
+      //^^^^^^^^^^^^ full_range
+        SyntaxKind {},
+      //^^^^^^^^^^^^^ kind
+        None,
+      //^^^^ docs
+    );
+}"#,
+        );
+    }
+
+    #[test]
+    fn omitted_parameters_hints_heuristics() {
+        check_with_config(
+            InlayHintsConfig { max_length: Some(8), ..Default::default() },
+            r#"
+fn map(f: i32) {}
+fn filter(predicate: i32) {}
+
+struct TestVarContainer {
+    test_var: i32,
+}
+
+impl TestVarContainer {
+    fn test_var(&self) -> i32 {
+        self.test_var
+    }
+}
+
+struct Test {}
+
+impl Test {
+    fn map(self, f: i32) -> Self {
+        self
+    }
+
+    fn filter(self, predicate: i32) -> Self {
+        self
+    }
+
+    fn field(self, value: i32) -> Self {
+        self
+    }
+
+    fn no_hints_expected(&self, _: i32, test_var: i32) {}
+
+    fn frob(&self, frob: bool) {}
+}
+
+struct Param {}
+
+fn different_order(param: &Param) {}
+fn different_order_mut(param: &mut Param) {}
+fn has_underscore(_param: bool) {}
+fn enum_matches_param_name(completion_kind: CompletionKind) {}
+fn param_destructuring_omitted_1((a, b): (u32, u32)) {}
+fn param_destructuring_omitted_2(TestVarContainer { test_var: _ }: TestVarContainer) {}
+
+fn twiddle(twiddle: bool) {}
+fn doo(_doo: bool) {}
+
+enum CompletionKind {
+    Keyword,
+}
+
+fn main() {
+    let container: TestVarContainer = TestVarContainer { test_var: 42 };
+    let test: Test = Test {};
+
+    map(22);
+    filter(33);
+
+    let test_processed: Test = test.map(1).filter(2).field(3);
+
+    let test_var: i32 = 55;
+    test_processed.no_hints_expected(22, test_var);
+    test_processed.no_hints_expected(33, container.test_var);
+    test_processed.no_hints_expected(44, container.test_var());
+    test_processed.frob(false);
+
+    twiddle(true);
+    doo(true);
+
+    let mut param_begin: Param = Param {};
+    different_order(&param_begin);
+    different_order(&mut param_begin);
+
+    let param: bool = true;
+    has_underscore(param);
+
+    enum_matches_param_name(CompletionKind::Keyword);
+
+    let a: f64 = 7.0;
+    let b: f64 = 4.0;
+    let _: f64 = a.div_euclid(b);
+    let _: f64 = a.abs_sub(b);
+
+    let range: (u32, u32) = (3, 5);
+    param_destructuring_omitted_1(range);
+    param_destructuring_omitted_2(container);
+}"#,
+        );
+    }
+
+    #[test]
+    fn unit_structs_have_no_type_hints() {
+        check_with_config(
+            InlayHintsConfig { max_length: Some(8), ..Default::default() },
+            r#"
+enum Result<T, E> { Ok(T), Err(E) }
+use Result::*;
+
+struct SyntheticSyntax;
+
+fn main() {
+    match Ok(()) {
+        Ok(_) => (),
+        Err(SyntheticSyntax) => (),
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn chaining_hints_ignore_comments() {
+        check_expect(
+            InlayHintsConfig {
+                parameter_hints: false,
+                type_hints: false,
+                chaining_hints: true,
+                max_length: None,
+            },
+            r#"
+struct A(B);
+impl A { fn into_b(self) -> B { self.0 } }
+struct B(C);
+impl B { fn into_c(self) -> C { self.0 } }
+struct C;
+
+fn main() {
+    let c = A(B(C))
+        .into_b() // This is a comment
+        .into_c();
+}
+"#,
+            expect![[r#"
+                [
+                    InlayHint {
+                        range: 147..172,
+                        kind: ChainingHint,
+                        label: "B",
+                    },
+                    InlayHint {
+                        range: 147..154,
+                        kind: ChainingHint,
+                        label: "A",
+                    },
+                ]
+            "#]],
+        );
+    }
+
+    #[test]
+    fn chaining_hints_without_newlines() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: false,
+                type_hints: false,
+                chaining_hints: true,
+                max_length: None,
+            },
+            r#"
+struct A(B);
+impl A { fn into_b(self) -> B { self.0 } }
+struct B(C);
+impl B { fn into_c(self) -> C { self.0 } }
+struct C;
+
+fn main() {
+    let c = A(B(C)).into_b().into_c();
+}"#,
+        );
+    }
+
+    #[test]
+    fn struct_access_chaining_hints() {
+        check_expect(
+            InlayHintsConfig {
+                parameter_hints: false,
+                type_hints: false,
+                chaining_hints: true,
+                max_length: None,
+            },
+            r#"
+struct A { pub b: B }
+struct B { pub c: C }
+struct C(pub bool);
+struct D;
+
+impl D {
+    fn foo(&self) -> i32 { 42 }
+}
+
+fn main() {
+    let x = A { b: B { c: C(true) } }
+        .b
+        .c
+        .0;
+    let x = D
+        .foo();
+}"#,
+            expect![[r#"
+                [
+                    InlayHint {
+                        range: 143..190,
+                        kind: ChainingHint,
+                        label: "C",
+                    },
+                    InlayHint {
+                        range: 143..179,
+                        kind: ChainingHint,
+                        label: "B",
+                    },
+                ]
+            "#]],
+        );
+    }
+
+    #[test]
+    fn generic_chaining_hints() {
+        check_expect(
+            InlayHintsConfig {
+                parameter_hints: false,
+                type_hints: false,
+                chaining_hints: true,
+                max_length: None,
+            },
+            r#"
+struct A<T>(T);
+struct B<T>(T);
+struct C<T>(T);
+struct X<T,R>(T, R);
+
+impl<T> A<T> {
+    fn new(t: T) -> Self { A(t) }
+    fn into_b(self) -> B<T> { B(self.0) }
+}
+impl<T> B<T> {
+    fn into_c(self) -> C<T> { C(self.0) }
+}
+fn main() {
+    let c = A::new(X(42, true))
+        .into_b()
+        .into_c();
+}
+"#,
+            expect![[r#"
+                [
+                    InlayHint {
+                        range: 246..283,
+                        kind: ChainingHint,
+                        label: "B<X<i32, bool>>",
+                    },
+                    InlayHint {
+                        range: 246..265,
+                        kind: ChainingHint,
+                        label: "A<X<i32, bool>>",
+                    },
+                ]
+            "#]],
+        );
+    }
+}