Merge #11755

11755: feat: Implement lifetime elision hints r=Veykril a=Veykril

With names on:
![Code_erl26zKvuf](https://user-images.githubusercontent.com/3757771/159134856-e2c75d2d-f17c-45c7-9a78-3da5ee8b1acd.png)
With names off:
![Code_MRP1Pbfe9d](https://user-images.githubusercontent.com/3757771/159134857-30fac3a1-825e-4f49-ba9b-9fa0bb215694.png)


Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

crates/ide/src/inlay_hints.rs

@@ -1,10 +1,13 @@
 use either::Either;
 use hir::{known, Callable, HasVisibility, HirDisplay, Semantics, TypeInfo};
-use ide_db::{base_db::FileRange, famous_defs::FamousDefs, RootDatabase};
+use ide_db::{
+    base_db::FileRange, famous_defs::FamousDefs, syntax_helpers::node_ext::walk_ty, RootDatabase,
+};
 use itertools::Itertools;
+use rustc_hash::FxHashMap;
 use stdx::to_lower_snake_case;
 use syntax::{
-    ast::{self, AstNode, HasArgList, HasName, UnaryOp},
+    ast::{self, AstNode, HasArgList, HasGenericParams, HasName, UnaryOp},
     match_ast, Direction, NodeOrToken, SmolStr, SyntaxKind, SyntaxNode, TextRange, T,
 };
 
@@ -17,16 +20,27 @@ pub struct InlayHintsConfig {
     pub parameter_hints: bool,
     pub chaining_hints: bool,
     pub closure_return_type_hints: bool,
+    pub lifetime_elision_hints: LifetimeElisionHints,
+    pub param_names_for_lifetime_elision_hints: bool,
     pub hide_named_constructor_hints: bool,
     pub max_length: Option<usize>,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum LifetimeElisionHints {
+    Always,
+    SkipTrivial,
+    Never,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum InlayKind {
     TypeHint,
     ParameterHint,
     ClosureReturnTypeHint,
     ChainingHint,
+    GenericParamListHint,
+    LifetimeHint,
 }
 
 #[derive(Debug)]
@@ -41,12 +55,17 @@ pub struct InlayHint {
 // 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 hints for
+// rust-analyzer by default shows hints for
 //
 // * types of local variables
 // * names of function arguments
 // * types of chained expressions
 //
+// Optionally, one can enable additional hints for
+//
+// * return types of closure expressions with blocks
+// * elided lifetimes
+//
 // **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].
@@ -108,11 +127,212 @@ fn hints(
             }
             _ => (),
         }
-    } else if let Some(it) = ast::IdentPat::cast(node) {
+    } else if let Some(it) = ast::IdentPat::cast(node.clone()) {
         bind_pat_hints(hints, sema, config, &it);
+    } else if let Some(it) = ast::Fn::cast(node) {
+        lifetime_hints(hints, config, it);
     }
 }
 
+fn lifetime_hints(
+    acc: &mut Vec<InlayHint>,
+    config: &InlayHintsConfig,
+    func: ast::Fn,
+) -> Option<()> {
+    if config.lifetime_elision_hints == LifetimeElisionHints::Never {
+        return None;
+    }
+    let param_list = func.param_list()?;
+    let generic_param_list = func.generic_param_list();
+    let ret_type = func.ret_type();
+    let self_param = param_list.self_param().filter(|it| it.amp_token().is_some());
+
+    let mut used_names: FxHashMap<SmolStr, usize> = generic_param_list
+        .iter()
+        .filter(|_| config.param_names_for_lifetime_elision_hints)
+        .flat_map(|gpl| gpl.lifetime_params())
+        .filter_map(|param| param.lifetime())
+        .filter_map(|lt| Some((SmolStr::from(lt.text().as_str().get(1..)?), 0)))
+        .collect();
+
+    let mut allocated_lifetimes = vec![];
+    let mut gen_idx_name = {
+        let mut gen = (0u8..).map(|idx| match idx {
+            idx if idx < 10 => SmolStr::from_iter(['\'', (idx + 48) as char]),
+            idx => format!("'{idx}").into(),
+        });
+        move || gen.next().unwrap_or_default()
+    };
+
+    let mut potential_lt_refs: Vec<_> = vec![];
+    param_list
+        .params()
+        .filter_map(|it| {
+            Some((
+                config.param_names_for_lifetime_elision_hints.then(|| it.pat()).flatten(),
+                it.ty()?,
+            ))
+        })
+        .for_each(|(pat, ty)| {
+            // FIXME: check path types
+            walk_ty(&ty, &mut |ty| match ty {
+                ast::Type::RefType(r) => potential_lt_refs.push((
+                    pat.as_ref().and_then(|it| match it {
+                        ast::Pat::IdentPat(p) => p.name(),
+                        _ => None,
+                    }),
+                    r,
+                )),
+                _ => (),
+            })
+        });
+
+    enum LifetimeKind {
+        Elided,
+        Named(SmolStr),
+        Static,
+    }
+
+    let fetch_lt_text = |lt: Option<ast::Lifetime>| match lt {
+        Some(lt) => match lt.text().as_str() {
+            "'_" => LifetimeKind::Elided,
+            "'static" => LifetimeKind::Static,
+            name => LifetimeKind::Named(name.into()),
+        },
+        None => LifetimeKind::Elided,
+    };
+    let is_elided = |lt: Option<ast::Lifetime>| match lt {
+        Some(lt) => matches!(lt.text().as_str(), "'_"),
+        None => true,
+    };
+
+    // allocate names
+    if let Some(self_param) = &self_param {
+        if is_elided(self_param.lifetime()) {
+            allocated_lifetimes.push(if config.param_names_for_lifetime_elision_hints {
+                // self can't be used as a lifetime, so no need to check for collisions
+                "'self".into()
+            } else {
+                gen_idx_name()
+            });
+        }
+    }
+    potential_lt_refs.iter().for_each(|(name, it)| {
+        if is_elided(it.lifetime()) {
+            let name = match name {
+                Some(it) => {
+                    if let Some(c) = used_names.get_mut(it.text().as_str()) {
+                        *c += 1;
+                        SmolStr::from(format!("'{text}{c}", text = it.text().as_str()))
+                    } else {
+                        used_names.insert(it.text().as_str().into(), 0);
+                        SmolStr::from_iter(["\'", it.text().as_str()])
+                    }
+                }
+                _ => gen_idx_name(),
+            };
+            allocated_lifetimes.push(name);
+        }
+    });
+
+    // fetch output lifetime if elision rule applies
+
+    let output = if let Some(self_param) = &self_param {
+        match fetch_lt_text(self_param.lifetime()) {
+            LifetimeKind::Elided => allocated_lifetimes.get(0).cloned(),
+            LifetimeKind::Named(name) => Some(name),
+            LifetimeKind::Static => None,
+        }
+    } else {
+        match potential_lt_refs.as_slice() {
+            [(_, r)] => match fetch_lt_text(r.lifetime()) {
+                LifetimeKind::Elided => allocated_lifetimes.get(0).cloned(),
+                LifetimeKind::Named(name) => Some(name),
+                LifetimeKind::Static => None,
+            },
+            [..] => None,
+        }
+    };
+
+    if allocated_lifetimes.is_empty() && output.is_none() {
+        return None;
+    }
+
+    // apply hints
+    // apply output if required
+    let mut is_trivial = true;
+    if let (Some(output_lt), Some(r)) = (&output, ret_type) {
+        if let Some(ty) = r.ty() {
+            walk_ty(&ty, &mut |ty| match ty {
+                ast::Type::RefType(ty) if ty.lifetime().is_none() => {
+                    if let Some(amp) = ty.amp_token() {
+                        is_trivial = false;
+                        acc.push(InlayHint {
+                            range: amp.text_range(),
+                            kind: InlayKind::LifetimeHint,
+                            label: output_lt.clone(),
+                        });
+                    }
+                }
+                _ => (),
+            })
+        }
+    }
+
+    if config.lifetime_elision_hints == LifetimeElisionHints::SkipTrivial && is_trivial {
+        return None;
+    }
+
+    let mut idx = match &self_param {
+        Some(self_param) if is_elided(self_param.lifetime()) => {
+            if let Some(amp) = self_param.amp_token() {
+                let lt = allocated_lifetimes[0].clone();
+                acc.push(InlayHint {
+                    range: amp.text_range(),
+                    kind: InlayKind::LifetimeHint,
+                    label: lt,
+                });
+            }
+            1
+        }
+        _ => 0,
+    };
+
+    for (_, p) in potential_lt_refs.iter() {
+        if is_elided(p.lifetime()) {
+            let t = p.amp_token()?;
+            let lt = allocated_lifetimes[idx].clone();
+            acc.push(InlayHint { range: t.text_range(), kind: InlayKind::LifetimeHint, label: lt });
+            idx += 1;
+        }
+    }
+
+    // generate generic param list things
+    match (generic_param_list, allocated_lifetimes.as_slice()) {
+        (_, []) => (),
+        (Some(gpl), allocated_lifetimes) => {
+            let angle_tok = gpl.l_angle_token()?;
+            let is_empty = gpl.generic_params().next().is_none();
+            acc.push(InlayHint {
+                range: angle_tok.text_range(),
+                kind: InlayKind::GenericParamListHint,
+                label: format!(
+                    "{}{}",
+                    allocated_lifetimes.iter().format(", "),
+                    if is_empty { "" } else { ", " }
+                )
+                .into(),
+            });
+        }
+        (None, allocated_lifetimes) => acc.push(InlayHint {
+            range: func.name()?.syntax().text_range(),
+            kind: InlayKind::GenericParamListHint,
+            label: format!("<{}>", allocated_lifetimes.iter().format(", "),).into(),
+        }),
+    }
+    Some(())
+}
+
 fn closure_ret_hints(
     acc: &mut Vec<InlayHint>,
     sema: &Semantics<RootDatabase>,
@@ -600,18 +820,21 @@ fn get_callable(
 mod tests {
     use expect_test::{expect, Expect};
     use ide_db::base_db::FileRange;
+    use itertools::Itertools;
     use syntax::{TextRange, TextSize};
     use test_utils::extract_annotations;
 
-    use crate::{fixture, inlay_hints::InlayHintsConfig};
+    use crate::{fixture, inlay_hints::InlayHintsConfig, LifetimeElisionHints};
 
     const DISABLED_CONFIG: InlayHintsConfig = InlayHintsConfig {
         render_colons: false,
         type_hints: false,
         parameter_hints: false,
         chaining_hints: false,
+        lifetime_elision_hints: LifetimeElisionHints::Never,
         hide_named_constructor_hints: false,
         closure_return_type_hints: false,
+        param_names_for_lifetime_elision_hints: false,
         max_length: None,
     };
     const TEST_CONFIG: InlayHintsConfig = InlayHintsConfig {
@@ -619,6 +842,7 @@ mod tests {
         parameter_hints: true,
         chaining_hints: true,
         closure_return_type_hints: true,
+        lifetime_elision_hints: LifetimeElisionHints::Always,
         ..DISABLED_CONFIG
     };
 
@@ -648,10 +872,15 @@ mod tests {
     #[track_caller]
     fn check_with_config(config: InlayHintsConfig, ra_fixture: &str) {
         let (analysis, file_id) = fixture::file(ra_fixture);
-        let expected = extract_annotations(&*analysis.file_text(file_id).unwrap());
+        let mut expected = extract_annotations(&*analysis.file_text(file_id).unwrap());
         let inlay_hints = analysis.inlay_hints(&config, file_id, None).unwrap();
-        let actual =
-            inlay_hints.into_iter().map(|it| (it.range, it.label.to_string())).collect::<Vec<_>>();
+        let actual = inlay_hints
+            .into_iter()
+            .map(|it| (it.range, it.label.to_string()))
+            .sorted_by_key(|(range, _)| range.start())
+            .collect::<Vec<_>>();
+        expected.sort_by_key(|(range, _)| range.start());
+
         assert_eq!(expected, actual, "\nExpected:\n{:#?}\n\nActual:\n{:#?}", expected, actual);
     }
 
@@ -1289,41 +1518,6 @@ fn main() {
         );
     }
 
-    #[test]
-    fn incomplete_for_no_hint() {
-        check_types(
-            r#"
-fn main() {
-    let data = &[1i32, 2, 3];
-      //^^^^ &[i32; 3]
-    for i
-}"#,
-        );
-        check(
-            r#"
-pub struct Vec<T> {}
-
-impl<T> Vec<T> {
-    pub fn new() -> Self { Vec {} }
-    pub fn push(&mut self, t: T) {}
-}
-
-impl<T> IntoIterator for Vec<T> {
-    type Item=T;
-}
-
-fn main() {
-    let mut data = Vec::new();
-          //^^^^ Vec<&str>
-    data.push("foo");
-    for i in
-
-    println!("Unit expr");
-}
-"#,
-        );
-    }
-
     #[test]
     fn complete_for_hint() {
         check_types(
@@ -1825,4 +2019,103 @@ fn main() {
             "#]],
         );
     }
+
+    #[test]
+    fn hints_lifetimes() {
+        check(
+            r#"
+fn empty() {}
+
+fn no_gpl(a: &()) {}
+ //^^^^^^<'0>
+          // ^'0
+fn empty_gpl<>(a: &()) {}
+      //    ^'0   ^'0
+fn partial<'b>(a: &(), b: &'b ()) {}
+//        ^'0, $  ^'0
+fn partial<'a>(a: &'a (), b: &()) {}
+//        ^'0, $             ^'0
+
+fn single_ret(a: &()) -> &() {}
+// ^^^^^^^^^^<'0>
+              // ^'0     ^'0
+fn full_mul(a: &(), b: &()) {}
+// ^^^^^^^^<'0, '1>
+            // ^'0     ^'1
+
+fn foo<'c>(a: &'c ()) -> &() {}
+                      // ^'c
+
+fn nested_in(a: &   &X< &()>) {}
+// ^^^^^^^^^<'0, '1, '2>
+              //^'0 ^'1 ^'2
+fn nested_out(a: &()) -> &   &X< &()>{}
+// ^^^^^^^^^^<'0>
+               //^'0     ^'0 ^'0 ^'0
+
+impl () {
+    fn foo(&self) {}
+    // ^^^<'0>
+        // ^'0
+    fn foo(&self) -> &() {}
+    // ^^^<'0>
+        // ^'0       ^'0
+    fn foo(&self, a: &()) -> &() {}
+    // ^^^<'0, '1>
+        // ^'0       ^'1     ^'0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn hints_lifetimes_named() {
+        check_with_config(
+            InlayHintsConfig { param_names_for_lifetime_elision_hints: true, ..TEST_CONFIG },
+            r#"
+fn nested_in<'named>(named: &        &X<      &()>) {}
+//          ^'named1, 'named2, 'named3, $
+                          //^'named1 ^'named2 ^'named3
+"#,
+        );
+    }
+
+    #[test]
+    fn hints_lifetimes_trivial_skip() {
+        check_with_config(
+            InlayHintsConfig {
+                lifetime_elision_hints: LifetimeElisionHints::SkipTrivial,
+                ..TEST_CONFIG
+            },
+            r#"
+fn no_gpl(a: &()) {}
+fn empty_gpl<>(a: &()) {}
+fn partial<'b>(a: &(), b: &'b ()) {}
+fn partial<'a>(a: &'a (), b: &()) {}
+
+fn single_ret(a: &()) -> &() {}
+// ^^^^^^^^^^<'0>
+              // ^'0     ^'0
+fn full_mul(a: &(), b: &()) {}
+
+fn foo<'c>(a: &'c ()) -> &() {}
+                      // ^'c
+
+fn nested_in(a: &   &X< &()>) {}
+fn nested_out(a: &()) -> &   &X< &()>{}
+// ^^^^^^^^^^<'0>
+               //^'0     ^'0 ^'0 ^'0
+
+impl () {
+    fn foo(&self) {}
+    fn foo(&self) -> &() {}
+    // ^^^<'0>
+        // ^'0       ^'0
+    fn foo(&self, a: &()) -> &() {}
+    // ^^^<'0, '1>
+        // ^'0       ^'1     ^'0
+}
+"#,
+        );
+    }
 }

crates/ide/src/lib.rs

@@ -80,7 +80,7 @@ pub use crate::{
     folding_ranges::{Fold, FoldKind},
     highlight_related::{HighlightRelatedConfig, HighlightedRange},
     hover::{HoverAction, HoverConfig, HoverDocFormat, HoverGotoTypeData, HoverResult},
-    inlay_hints::{InlayHint, InlayHintsConfig, InlayKind},
+    inlay_hints::{InlayHint, InlayHintsConfig, InlayKind, LifetimeElisionHints},
     join_lines::JoinLinesConfig,
     markup::Markup,
     moniker::{MonikerKind, MonikerResult, PackageInformation},

crates/ide/src/static_index.rs

@@ -12,11 +12,14 @@ use ide_db::{
 use rustc_hash::FxHashSet;
 use syntax::{AstNode, SyntaxKind::*, SyntaxToken, TextRange, T};
 
-use crate::moniker::{crate_for_file, def_to_moniker, MonikerResult};
 use crate::{
     hover::hover_for_definition, Analysis, Fold, HoverConfig, HoverDocFormat, HoverResult,
     InlayHint, InlayHintsConfig, TryToNav,
 };
+use crate::{
+    moniker::{crate_for_file, def_to_moniker, MonikerResult},
+    LifetimeElisionHints,
+};
 
 /// A static representation of fully analyzed source code.
 ///
@@ -110,7 +113,9 @@ impl StaticIndex<'_> {
                     parameter_hints: true,
                     chaining_hints: true,
                     closure_return_type_hints: true,
+                    lifetime_elision_hints: LifetimeElisionHints::Never,
                     hide_named_constructor_hints: false,
+                    param_names_for_lifetime_elision_hints: false,
                     max_length: Some(25),
                 },
                 file_id,

crates/rust-analyzer/src/config.rs

@@ -12,7 +12,8 @@ use std::{ffi::OsString, iter, path::PathBuf};
 use flycheck::FlycheckConfig;
 use ide::{
     AssistConfig, CompletionConfig, DiagnosticsConfig, ExprFillDefaultMode, HighlightRelatedConfig,
-    HoverConfig, HoverDocFormat, InlayHintsConfig, JoinLinesConfig, Snippet, SnippetScope,
+    HoverConfig, HoverDocFormat, InlayHintsConfig, JoinLinesConfig, LifetimeElisionHints, Snippet,
+    SnippetScope,
 };
 use ide_db::{
     imports::insert_use::{ImportGranularity, InsertUseConfig, PrefixKind},
@@ -243,20 +244,24 @@ config_data! {
         hoverActions_run: bool             = "true",
 
         /// Whether to render trailing colons for parameter hints, and trailing colons for parameter hints.
-        inlayHints_renderColons: bool               = "true",
+        inlayHints_renderColons: bool                      = "true",
         /// Maximum length for inlay hints. Set to null to have an unlimited length.
-        inlayHints_maxLength: Option<usize>         = "25",
+        inlayHints_maxLength: Option<usize>                = "25",
         /// Whether to show function parameter name inlay hints at the call
         /// site.
-        inlayHints_parameterHints: bool             = "true",
+        inlayHints_parameterHints: bool                     = "true",
         /// Whether to show inlay type hints for variables.
-        inlayHints_typeHints: bool                  = "true",
+        inlayHints_typeHints: bool                          = "true",
         /// Whether to show inlay type hints for method chains.
-        inlayHints_chainingHints: bool              = "true",
+        inlayHints_chainingHints: bool                      = "true",
         /// Whether to show inlay type hints for return types of closures with blocks.
-        inlayHints_closureReturnTypeHints: bool     = "false",
+        inlayHints_closureReturnTypeHints: bool             = "false",
+        /// Whether to show inlay type hints for elided lifetimes in function signatures.
+        inlayHints_lifetimeElisionHints: LifetimeElisionDef = "\"never\"",
+        /// Whether to prefer using parameter names as the name for elided lifetime hints if possible.
+        inlayHints_lifetimeElisionHints_useParameterNames: bool  = "false",
         /// Whether to hide inlay hints for constructors.
-        inlayHints_hideNamedConstructorHints: bool  = "false",
+        inlayHints_hideNamedConstructorHints: bool          = "false",
 
         /// Join lines inserts else between consecutive ifs.
         joinLines_joinElseIf: bool = "true",
@@ -855,7 +860,15 @@ impl Config {
             parameter_hints: self.data.inlayHints_parameterHints,
             chaining_hints: self.data.inlayHints_chainingHints,
             closure_return_type_hints: self.data.inlayHints_closureReturnTypeHints,
+            lifetime_elision_hints: match self.data.inlayHints_lifetimeElisionHints {
+                LifetimeElisionDef::Always => LifetimeElisionHints::Always,
+                LifetimeElisionDef::Never => LifetimeElisionHints::Never,
+                LifetimeElisionDef::SkipTrivial => LifetimeElisionHints::SkipTrivial,
+            },
             hide_named_constructor_hints: self.data.inlayHints_hideNamedConstructorHints,
+            param_names_for_lifetime_elision_hints: self
+                .data
+                .inlayHints_lifetimeElisionHints_useParameterNames,
             max_length: self.data.inlayHints_maxLength,
         }
     }
@@ -1125,6 +1138,16 @@ enum ImportGranularityDef {
     Module,
 }
 
+#[derive(Deserialize, Debug, Clone)]
+#[serde(rename_all = "snake_case")]
+enum LifetimeElisionDef {
+    #[serde(alias = "true")]
+    Always,
+    #[serde(alias = "false")]
+    Never,
+    SkipTrivial,
+}
+
 #[derive(Deserialize, Debug, Clone)]
 #[serde(rename_all = "snake_case")]
 enum ImportPrefixDef {
@@ -1377,7 +1400,16 @@ fn field_props(field: &str, ty: &str, doc: &[&str], default: &str) -> serde_json
             "minimum": 0,
             "maximum": 255
         },
-        _ => panic!("{}: {}", ty, default),
+        "LifetimeElisionDef" => set! {
+            "type": "string",
+            "enum": ["always", "never", "skip_trivial"],
+            "enumDescriptions": [
+                "Always show lifetime elision hints.",
+                "Never show lifetime elision hints.",
+                "Only show lifetime elision hints if a return type is involved."
+            ],
+        },
+        _ => panic!("missing entry for {}: {}", ty, default),
     }
 
     map.into()

crates/rust-analyzer/src/to_proto.rs

@@ -427,27 +427,34 @@ pub(crate) fn inlay_hint(
         }),
         position: match inlay_hint.kind {
             InlayKind::ParameterHint => position(line_index, inlay_hint.range.start()),
-            InlayKind::ClosureReturnTypeHint | InlayKind::TypeHint | InlayKind::ChainingHint => {
-                position(line_index, inlay_hint.range.end())
-            }
+            InlayKind::ClosureReturnTypeHint
+            | InlayKind::TypeHint
+            | InlayKind::ChainingHint
+            | InlayKind::GenericParamListHint
+            | InlayKind::LifetimeHint => position(line_index, inlay_hint.range.end()),
         },
         kind: match inlay_hint.kind {
             InlayKind::ParameterHint => Some(lsp_ext::InlayHintKind::PARAMETER),
             InlayKind::ClosureReturnTypeHint | InlayKind::TypeHint | InlayKind::ChainingHint => {
                 Some(lsp_ext::InlayHintKind::TYPE)
             }
+            InlayKind::GenericParamListHint | InlayKind::LifetimeHint => None,
         },
         tooltip: None,
         padding_left: Some(match inlay_hint.kind {
             InlayKind::TypeHint => !render_colons,
             InlayKind::ParameterHint | InlayKind::ClosureReturnTypeHint => false,
             InlayKind::ChainingHint => true,
+            InlayKind::GenericParamListHint => false,
+            InlayKind::LifetimeHint => false,
         }),
         padding_right: Some(match inlay_hint.kind {
             InlayKind::TypeHint | InlayKind::ChainingHint | InlayKind::ClosureReturnTypeHint => {
                 false
             }
             InlayKind::ParameterHint => true,
+            InlayKind::LifetimeHint => true,
+            InlayKind::GenericParamListHint => false,
         }),
     }
 }

crates/test_utils/src/lib.rs

@@ -306,15 +306,15 @@ fn extract_line_annotations(mut line: &str) -> Vec<LineAnnotation> {
         let end_marker = line_no_caret.find(|c| c == '$');
         let next = line_no_caret.find(marker).map_or(line.len(), |it| it + len);
 
-        let mut content = match end_marker {
-            Some(end_marker)
-                if end_marker < next
-                    && line_no_caret[end_marker..]
+        let cond = |end_marker| {
+            end_marker < next
+                && (line_no_caret[end_marker + 1..].is_empty()
+                    || line_no_caret[end_marker + 1..]
                         .strip_prefix(|c: char| c.is_whitespace() || c == '^')
-                        .is_some() =>
-            {
-                &line_no_caret[..end_marker]
-            }
+                        .is_some())
+        };
+        let mut content = match end_marker {
+            Some(end_marker) if cond(end_marker) => &line_no_caret[..end_marker],
             _ => line_no_caret[..next - len].trim_end(),
         };
 

docs/user/generated_config.adoc

@@ -378,6 +378,16 @@ Whether to show inlay type hints for method chains.
 --
 Whether to show inlay type hints for return types of closures with blocks.
 --
+[[rust-analyzer.inlayHints.lifetimeElisionHints]]rust-analyzer.inlayHints.lifetimeElisionHints (default: `"never"`)::
++
+--
+Whether to show inlay type hints for elided lifetimes in function signatures.
+--
+[[rust-analyzer.inlayHints.lifetimeElisionHints.useParameterNames]]rust-analyzer.inlayHints.lifetimeElisionHints.useParameterNames (default: `false`)::
++
+--
+Whether to prefer using parameter names as the name for elided lifetime hints if possible.
+--
 [[rust-analyzer.inlayHints.hideNamedConstructorHints]]rust-analyzer.inlayHints.hideNamedConstructorHints (default: `false`)::
 +
 --

editors/code/package.json

@@ -795,6 +795,26 @@
                     "default": false,
                     "type": "boolean"
                 },
+                "rust-analyzer.inlayHints.lifetimeElisionHints": {
+                    "markdownDescription": "Whether to show inlay type hints for elided lifetimes in function signatures.",
+                    "default": "never",
+                    "type": "string",
+                    "enum": [
+                        "always",
+                        "never",
+                        "skip_trivial"
+                    ],
+                    "enumDescriptions": [
+                        "Always show lifetime elision hints.",
+                        "Never show lifetime elision hints.",
+                        "Only show lifetime elision hints if a return type is involved."
+                    ]
+                },
+                "rust-analyzer.inlayHints.lifetimeElisionHints.useParameterNames": {
+                    "markdownDescription": "Whether to prefer using parameter names as the name for elided lifetime hints if possible.",
+                    "default": false,
+                    "type": "boolean"
+                },
                 "rust-analyzer.inlayHints.hideNamedConstructorHints": {
                     "markdownDescription": "Whether to hide inlay hints for constructors.",
                     "default": false,