8 files changed, 395 insertions, 5 deletions

diff --git a/crates/ra_assists/src/handlers/change_lifetime_anon_to_named.rs b/crates/ra_assists/src/handlers/change_lifetime_anon_to_named.rs
new file mode 100644
index 000000000..999aec421
--- /dev/null
+++ b/crates/ra_assists/src/handlers/change_lifetime_anon_to_named.rs
@@ -0,0 +1,303 @@
+use crate::{assist_context::AssistBuilder, AssistContext, AssistId, Assists};
+use ast::{NameOwner, ParamList, TypeAscriptionOwner, TypeParamList, TypeRef};
+use ra_syntax::{ast, ast::TypeParamsOwner, AstNode, SyntaxKind, TextRange, TextSize};
+use rustc_hash::FxHashSet;
+
+static ASSIST_NAME: &str = "change_lifetime_anon_to_named";
+static ASSIST_LABEL: &str = "Give anonymous lifetime a name";
+
+// Assist: change_lifetime_anon_to_named
+//
+// Change an anonymous lifetime to a named lifetime.
+//
+// ```
+// impl Cursor<'_<|>> {
+//     fn node(self) -> &SyntaxNode {
+//         match self {
+//             Cursor::Replace(node) | Cursor::Before(node) => node,
+//         }
+//     }
+// }
+// ```
+// ->
+// ```
+// impl<'a> Cursor<'a> {
+//     fn node(self) -> &SyntaxNode {
+//         match self {
+//             Cursor::Replace(node) | Cursor::Before(node) => node,
+//         }
+//     }
+// }
+// ```
+// FIXME: How can we handle renaming any one of multiple anonymous lifetimes?
+// FIXME: should also add support for the case fun(f: &Foo) -> &<|>Foo
+pub(crate) fn change_lifetime_anon_to_named(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let lifetime_token = ctx
+        .find_token_at_offset(SyntaxKind::LIFETIME)
+        .filter(|lifetime| lifetime.text() == "'_")?;
+    if let Some(fn_def) = lifetime_token.ancestors().find_map(ast::FnDef::cast) {
+        generate_fn_def_assist(acc, &fn_def, lifetime_token.text_range())
+    } else if let Some(impl_def) = lifetime_token.ancestors().find_map(ast::ImplDef::cast) {
+        // only allow naming the last anonymous lifetime
+        lifetime_token.next_token().filter(|tok| tok.kind() == SyntaxKind::R_ANGLE)?;
+        generate_impl_def_assist(acc, &impl_def, lifetime_token.text_range())
+    } else {
+        None
+    }
+}
+
+/// Generate the assist for the fn def case
+fn generate_fn_def_assist(
+    acc: &mut Assists,
+    fn_def: &ast::FnDef,
+    lifetime_loc: TextRange,
+) -> Option<()> {
+    let param_list: ParamList = fn_def.param_list()?;
+    let new_lifetime_param = generate_unique_lifetime_param_name(&fn_def.type_param_list())?;
+    let end_of_fn_ident = fn_def.name()?.ident_token()?.text_range().end();
+    let self_param =
+        // use the self if it's a reference and has no explicit lifetime
+        param_list.self_param().filter(|p| p.lifetime_token().is_none() && p.amp_token().is_some());
+    // compute the location which implicitly has the same lifetime as the anonymous lifetime
+    let loc_needing_lifetime = if let Some(self_param) = self_param {
+        // if we have a self reference, use that
+        Some(self_param.self_token()?.text_range().start())
+    } else {
+        // otherwise, if there's a single reference parameter without a named liftime, use that
+        let fn_params_without_lifetime: Vec<_> = param_list
+            .params()
+            .filter_map(|param| match param.ascribed_type() {
+                Some(TypeRef::ReferenceType(ascribed_type))
+                    if ascribed_type.lifetime_token() == None =>
+                {
+                    Some(ascribed_type.amp_token()?.text_range().end())
+                }
+                _ => None,
+            })
+            .collect();
+        match fn_params_without_lifetime.len() {
+            1 => Some(fn_params_without_lifetime.into_iter().nth(0)?),
+            0 => None,
+            // multiple unnnamed is invalid. assist is not applicable
+            _ => return None,
+        }
+    };
+    acc.add(AssistId(ASSIST_NAME), ASSIST_LABEL, lifetime_loc, |builder| {
+        add_lifetime_param(fn_def, builder, end_of_fn_ident, new_lifetime_param);
+        builder.replace(lifetime_loc, format!("'{}", new_lifetime_param));
+        loc_needing_lifetime.map(|loc| builder.insert(loc, format!("'{} ", new_lifetime_param)));
+    })
+}
+
+/// Generate the assist for the impl def case
+fn generate_impl_def_assist(
+    acc: &mut Assists,
+    impl_def: &ast::ImplDef,
+    lifetime_loc: TextRange,
+) -> Option<()> {
+    let new_lifetime_param = generate_unique_lifetime_param_name(&impl_def.type_param_list())?;
+    let end_of_impl_kw = impl_def.impl_token()?.text_range().end();
+    acc.add(AssistId(ASSIST_NAME), ASSIST_LABEL, lifetime_loc, |builder| {
+        add_lifetime_param(impl_def, builder, end_of_impl_kw, new_lifetime_param);
+        builder.replace(lifetime_loc, format!("'{}", new_lifetime_param));
+    })
+}
+
+/// Given a type parameter list, generate a unique lifetime parameter name
+/// which is not in the list
+fn generate_unique_lifetime_param_name(
+    existing_type_param_list: &Option<TypeParamList>,
+) -> Option<char> {
+    match existing_type_param_list {
+        Some(type_params) => {
+            let used_lifetime_params: FxHashSet<_> = type_params
+                .lifetime_params()
+                .map(|p| p.syntax().text().to_string()[1..].to_owned())
+                .collect();
+            (b'a'..=b'z').map(char::from).find(|c| !used_lifetime_params.contains(&c.to_string()))
+        }
+        None => Some('a'),
+    }
+}
+
+/// Add the lifetime param to `builder`. If there are type parameters in `type_params_owner`, add it to the end. Otherwise
+/// add new type params brackets with the lifetime parameter at `new_type_params_loc`.
+fn add_lifetime_param<TypeParamsOwner: ast::TypeParamsOwner>(
+    type_params_owner: &TypeParamsOwner,
+    builder: &mut AssistBuilder,
+    new_type_params_loc: TextSize,
+    new_lifetime_param: char,
+) {
+    match type_params_owner.type_param_list() {
+        // add the new lifetime parameter to an existing type param list
+        Some(type_params) => {
+            builder.insert(
+                (u32::from(type_params.syntax().text_range().end()) - 1).into(),
+                format!(", '{}", new_lifetime_param),
+            );
+        }
+        // create a new type param list containing only the new lifetime parameter
+        None => {
+            builder.insert(new_type_params_loc, format!("<'{}>", new_lifetime_param));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn test_example_case() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl Cursor<'_<|>> {
+                fn node(self) -> &SyntaxNode {
+                    match self {
+                        Cursor::Replace(node) | Cursor::Before(node) => node,
+                    }
+                }
+            }"#,
+            r#"impl<'a> Cursor<'a> {
+                fn node(self) -> &SyntaxNode {
+                    match self {
+                        Cursor::Replace(node) | Cursor::Before(node) => node,
+                    }
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn test_example_case_simplified() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl Cursor<'_<|>> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_example_case_cursor_after_tick() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl Cursor<'<|>_> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_example_case_cursor_before_tick() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl Cursor<<|>'_> {"#,
+            r#"impl<'a> Cursor<'a> {"#,
+        );
+    }
+
+    #[test]
+    fn test_not_applicable_cursor_position() {
+        check_assist_not_applicable(change_lifetime_anon_to_named, r#"impl Cursor<'_><|> {"#);
+        check_assist_not_applicable(change_lifetime_anon_to_named, r#"impl Cursor<|><'_> {"#);
+    }
+
+    #[test]
+    fn test_not_applicable_lifetime_already_name() {
+        check_assist_not_applicable(change_lifetime_anon_to_named, r#"impl Cursor<'a<|>> {"#);
+        check_assist_not_applicable(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun<'a>() -> X<'a<|>>"#,
+        );
+    }
+
+    #[test]
+    fn test_with_type_parameter() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl<T> Cursor<T, '_<|>>"#,
+            r#"impl<T, 'a> Cursor<T, 'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_with_existing_lifetime_name_conflict() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"impl<'a, 'b> Cursor<'a, 'b, '_<|>>"#,
+            r#"impl<'a, 'b, 'c> Cursor<'a, 'b, 'c>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_return_value_anon_lifetime_param() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun() -> X<'_<|>>"#,
+            r#"fn my_fun<'a>() -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_return_value_anon_reference_lifetime() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun() -> &'_<|> X"#,
+            r#"fn my_fun<'a>() -> &'a X"#,
+        );
+    }
+
+    #[test]
+    fn test_function_param_anon_lifetime() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun(x: X<'_<|>>)"#,
+            r#"fn my_fun<'a>(x: X<'a>)"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_params() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun(f: &Foo) -> X<'_<|>>"#,
+            r#"fn my_fun<'a>(f: &'a Foo) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_params_in_presence_of_other_lifetime() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun<'other>(f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(f: &'a Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_not_applicable_without_self_and_multiple_unnamed_param_lifetimes() {
+        // this is not permitted under lifetime elision rules
+        check_assist_not_applicable(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun(f: &Foo, b: &Bar) -> X<'_<|>>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_self_ref_param() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun<'other>(&self, f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(&'a self, f: &Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+
+    #[test]
+    fn test_function_add_lifetime_to_param_with_non_ref_self() {
+        check_assist(
+            change_lifetime_anon_to_named,
+            r#"fn my_fun<'other>(self, f: &Foo, b: &'other Bar) -> X<'_<|>>"#,
+            r#"fn my_fun<'other, 'a>(self, f: &'a Foo, b: &'other Bar) -> X<'a>"#,
+        );
+    }
+}
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 464bc03dd..3f8f7ffbf 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -112,6 +112,7 @@ mod handlers {
     mod add_turbo_fish;
     mod apply_demorgan;
     mod auto_import;
+    mod change_lifetime_anon_to_named;
     mod change_return_type_to_result;
     mod change_visibility;
     mod early_return;
@@ -151,6 +152,7 @@ mod handlers {
             add_turbo_fish::add_turbo_fish,
             apply_demorgan::apply_demorgan,
             auto_import::auto_import,
+            change_lifetime_anon_to_named::change_lifetime_anon_to_named,
             change_return_type_to_result::change_return_type_to_result,
             change_visibility::change_visibility,
             early_return::convert_to_guarded_return,
diff --git a/crates/ra_assists/src/tests/generated.rs b/crates/ra_assists/src/tests/generated.rs
index 4e0536828..73d43283d 100644
--- a/crates/ra_assists/src/tests/generated.rs
+++ b/crates/ra_assists/src/tests/generated.rs
@@ -288,6 +288,31 @@ pub mod std { pub mod collections { pub struct HashMap { } } }
 }
 
 #[test]
+fn doctest_change_lifetime_anon_to_named() {
+    check_doc_test(
+        "change_lifetime_anon_to_named",
+        r#####"
+impl Cursor<'_<|>> {
+    fn node(self) -> &SyntaxNode {
+        match self {
+            Cursor::Replace(node) | Cursor::Before(node) => node,
+        }
+    }
+}
+"#####,
+        r#####"
+impl<'a> Cursor<'a> {
+    fn node(self) -> &SyntaxNode {
+        match self {
+            Cursor::Replace(node) | Cursor::Before(node) => node,
+        }
+    }
+}
+"#####,
+    )
+}
+
+#[test]
 fn doctest_change_return_type_to_result() {
     check_doc_test(
         "change_return_type_to_result",
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 54bab3476..78084cb57 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -140,13 +140,13 @@ impl<'a> InferenceContext<'a> {
 
                 let mut sig_tys = Vec::new();
 
-                for (arg_pat, arg_type) in args.iter().zip(arg_types.iter()) {
-                    let expected = if let Some(type_ref) = arg_type {
+                // collect explicitly written argument types
+                for arg_type in arg_types.iter() {
+                    let arg_ty = if let Some(type_ref) = arg_type {
                         self.make_ty(type_ref)
                     } else {
-                        Ty::Unknown
+                        self.table.new_type_var()
                     };
-                    let arg_ty = self.infer_pat(*arg_pat, &expected, BindingMode::default());
                     sig_tys.push(arg_ty);
                 }
 
@@ -158,7 +158,7 @@ impl<'a> InferenceContext<'a> {
                 sig_tys.push(ret_ty.clone());
                 let sig_ty = Ty::apply(
                     TypeCtor::FnPtr { num_args: sig_tys.len() as u16 - 1 },
-                    Substs(sig_tys.into()),
+                    Substs(sig_tys.clone().into()),
                 );
                 let closure_ty =
                     Ty::apply_one(TypeCtor::Closure { def: self.owner, expr: tgt_expr }, sig_ty);
@@ -168,6 +168,12 @@ impl<'a> InferenceContext<'a> {
                 // infer the body.
                 self.coerce(&closure_ty, &expected.ty);
 
+                // Now go through the argument patterns
+                for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
+                    let resolved = self.resolve_ty_as_possible(arg_ty);
+                    self.infer_pat(*arg_pat, &resolved, BindingMode::default());
+                }
+
                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
                 let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
 
diff --git a/crates/ra_hir_ty/src/tests/patterns.rs b/crates/ra_hir_ty/src/tests/patterns.rs
index 0c5f972a2..fe62587c0 100644
--- a/crates/ra_hir_ty/src/tests/patterns.rs
+++ b/crates/ra_hir_ty/src/tests/patterns.rs
@@ -520,3 +520,53 @@ fn main() {
         105..107 '()': ()
     ")
 }
+
+#[test]
+fn match_ergonomics_in_closure_params() {
+    assert_snapshot!(
+        infer(r#"
+#[lang = "fn_once"]
+trait FnOnce<Args> {
+    type Output;
+}
+
+fn foo<T, U, F: FnOnce(T) -> U>(t: T, f: F) -> U { loop {} }
+
+fn test() {
+    foo(&(1, "a"), |&(x, y)| x); // normal, no match ergonomics
+    foo(&(1, "a"), |(x, y)| x);
+}
+"#),
+        @r###"
+    94..95 't': T
+    100..101 'f': F
+    111..122 '{ loop {} }': U
+    113..120 'loop {}': !
+    118..120 '{}': ()
+    134..233 '{     ... x); }': ()
+    140..143 'foo': fn foo<&(i32, &str), i32, |&(i32, &str)| -> i32>(&(i32, &str), |&(i32, &str)| -> i32) -> i32
+    140..167 'foo(&(...y)| x)': i32
+    144..153 '&(1, "a")': &(i32, &str)
+    145..153 '(1, "a")': (i32, &str)
+    146..147 '1': i32
+    149..152 '"a"': &str
+    155..166 '|&(x, y)| x': |&(i32, &str)| -> i32
+    156..163 '&(x, y)': &(i32, &str)
+    157..163 '(x, y)': (i32, &str)
+    158..159 'x': i32
+    161..162 'y': &str
+    165..166 'x': i32
+    204..207 'foo': fn foo<&(i32, &str), &i32, |&(i32, &str)| -> &i32>(&(i32, &str), |&(i32, &str)| -> &i32) -> &i32
+    204..230 'foo(&(...y)| x)': &i32
+    208..217 '&(1, "a")': &(i32, &str)
+    209..217 '(1, "a")': (i32, &str)
+    210..211 '1': i32
+    213..216 '"a"': &str
+    219..229 '|(x, y)| x': |&(i32, &str)| -> &i32
+    220..226 '(x, y)': (i32, &str)
+    221..222 'x': &i32
+    224..225 'y': &&str
+    228..229 'x': &i32
+    "###
+    );
+}
diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index 3ab1f0a21..0b53ebe69 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -398,6 +398,7 @@ fn highlight_element(
         INT_NUMBER | FLOAT_NUMBER => HighlightTag::NumericLiteral.into(),
         BYTE => HighlightTag::ByteLiteral.into(),
         CHAR => HighlightTag::CharLiteral.into(),
+        QUESTION => Highlight::new(HighlightTag::Operator) | HighlightModifier::ControlFlow,
         LIFETIME => {
             let h = Highlight::new(HighlightTag::Lifetime);
             match element.parent().map(|it| it.kind()) {
diff --git a/crates/ra_ide/src/syntax_highlighting/tags.rs b/crates/ra_ide/src/syntax_highlighting/tags.rs
index 46c718c91..1514531de 100644
--- a/crates/ra_ide/src/syntax_highlighting/tags.rs
+++ b/crates/ra_ide/src/syntax_highlighting/tags.rs
@@ -42,6 +42,7 @@ pub enum HighlightTag {
     Local,
     UnresolvedReference,
     FormatSpecifier,
+    Operator,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
@@ -89,6 +90,7 @@ impl HighlightTag {
             HighlightTag::Local => "variable",
             HighlightTag::UnresolvedReference => "unresolved_reference",
             HighlightTag::FormatSpecifier => "format_specifier",
+            HighlightTag::Operator => "operator",
         }
     }
 }
diff --git a/crates/rust-analyzer/src/to_proto.rs b/crates/rust-analyzer/src/to_proto.rs
index 8e8e7033d..2fbbb4e63 100644
--- a/crates/rust-analyzer/src/to_proto.rs
+++ b/crates/rust-analyzer/src/to_proto.rs
@@ -317,6 +317,7 @@ fn semantic_token_type_and_modifiers(
         HighlightTag::Keyword => lsp_types::SemanticTokenType::KEYWORD,
         HighlightTag::UnresolvedReference => semantic_tokens::UNRESOLVED_REFERENCE,
         HighlightTag::FormatSpecifier => semantic_tokens::FORMAT_SPECIFIER,
+        HighlightTag::Operator => lsp_types::SemanticTokenType::OPERATOR,
     };
 
     for modifier in highlight.modifiers.iter() {