Add signature help for tuple struct patterns

crates/ide/src/signature_help.rs

@@ -109,7 +109,13 @@ pub(crate) fn signature_help(db: &RootDatabase, position: FilePosition) -> Optio
                     }
                     return signature_help_for_record_pat(&sema, record, token);
                 },
-                ast::TupleStructPat(tuple_pat) => {},
+                ast::TupleStructPat(tuple_pat) => {
+                    let cursor_outside = tuple_pat.r_paren_token().as_ref() == Some(&token);
+                    if cursor_outside {
+                        continue;
+                    }
+                    return signature_help_for_tuple_struct_pat(&sema, tuple_pat, token);
+                },
                 _ => (),
             }
         }
@@ -367,6 +373,90 @@ fn signature_help_for_record_lit(
     )
 }
 
+fn signature_help_for_record_pat(
+    sema: &Semantics<'_, RootDatabase>,
+    record: ast::RecordPat,
+    token: SyntaxToken,
+) -> Option<SignatureHelp> {
+    signature_help_for_record_(
+        sema,
+        record.record_pat_field_list()?.syntax().children_with_tokens(),
+        &record.path()?,
+        record
+            .record_pat_field_list()?
+            .fields()
+            .filter_map(|field| sema.resolve_record_pat_field(&field)),
+        token,
+    )
+}
+
+fn signature_help_for_tuple_struct_pat(
+    sema: &Semantics<'_, RootDatabase>,
+    pat: ast::TupleStructPat,
+    token: SyntaxToken,
+) -> Option<SignatureHelp> {
+    let rest_pat = pat.fields().find(|it| matches!(it, ast::Pat::RestPat(_)));
+    let is_left_of_rest_pat =
+        rest_pat.map_or(true, |it| token.text_range().start() < it.syntax().text_range().end());
+
+    let mut res = SignatureHelp {
+        doc: None,
+        signature: String::new(),
+        parameters: vec![],
+        active_parameter: None,
+    };
+
+    let db = sema.db;
+    let path_res = sema.resolve_path(&pat.path()?)?;
+    let fields: Vec<_> = if let PathResolution::Def(ModuleDef::Variant(variant)) = path_res {
+        let en = variant.parent_enum(db);
+
+        res.doc = en.docs(db).map(|it| it.into());
+        format_to!(res.signature, "enum {}::{} (", en.name(db), variant.name(db));
+        variant.fields(db)
+    } else {
+        let adt = match path_res {
+            PathResolution::SelfType(imp) => imp.self_ty(db).as_adt()?,
+            PathResolution::Def(ModuleDef::Adt(adt)) => adt,
+            _ => return None,
+        };
+
+        match adt {
+            hir::Adt::Struct(it) => {
+                res.doc = it.docs(db).map(|it| it.into());
+                format_to!(res.signature, "struct {} (", it.name(db));
+                it.fields(db)
+            }
+            _ => return None,
+        }
+    };
+    let commas = pat
+        .syntax()
+        .children_with_tokens()
+        .filter_map(syntax::NodeOrToken::into_token)
+        .filter(|t| t.kind() == syntax::T![,]);
+    res.active_parameter = Some(if is_left_of_rest_pat {
+        commas.take_while(|t| t.text_range().start() <= token.text_range().start()).count()
+    } else {
+        let n_commas = commas
+            .collect::<Vec<_>>()
+            .into_iter()
+            .rev()
+            .take_while(|t| t.text_range().start() > token.text_range().start())
+            .count();
+        fields.len().saturating_sub(1).saturating_sub(n_commas)
+    });
+
+    let mut buf = String::new();
+    for ty in fields.into_iter().map(|it| it.ty(db)) {
+        format_to!(buf, "{}", ty.display_truncated(db, Some(20)));
+        res.push_call_param(&buf);
+        buf.clear();
+    }
+    res.signature.push_str(")");
+    Some(res)
+}
+
 fn signature_help_for_record_(
     sema: &Semantics<'_, RootDatabase>,
     field_list_children: SyntaxElementChildren,
@@ -442,23 +532,6 @@ fn signature_help_for_record_(
     Some(res)
 }
 
-fn signature_help_for_record_pat(
-    sema: &Semantics<'_, RootDatabase>,
-    record: ast::RecordPat,
-    token: SyntaxToken,
-) -> Option<SignatureHelp> {
-    signature_help_for_record_(
-        sema,
-        record.record_pat_field_list()?.syntax().children_with_tokens(),
-        &record.path()?,
-        record
-            .record_pat_field_list()?
-            .fields()
-            .filter_map(|field| sema.resolve_record_pat_field(&field)),
-        token,
-    )
-}
-
 #[cfg(test)]
 mod tests {
     use std::iter;
@@ -480,6 +553,7 @@ pub(crate) fn position(ra_fixture: &str) -> (RootDatabase, FilePosition) {
         (database, FilePosition { file_id, offset })
     }
 
+    #[track_caller]
     fn check(ra_fixture: &str, expect: Expect) {
         let fixture = format!(
             r#"
@@ -931,6 +1005,119 @@ struct S(u32, i32)
         );
     }
 
+    #[test]
+    fn tuple_struct_pat() {
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32);
+fn main() {
+    let S(0, $0);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32)
+                          ---  ^^^
+            "#]],
+        );
+    }
+
+    #[test]
+    fn tuple_struct_pat_rest() {
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16);
+fn main() {
+    let S(0, .., $0);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16)
+                          ---  ---  ---  ^^^
+            "#]],
+        );
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16, u8);
+fn main() {
+    let S(0, .., $0, 0);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16, u8)
+                          ---  ---  ---  ^^^  --
+            "#]],
+        );
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16);
+fn main() {
+    let S($0, .., 1);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16)
+                          ^^^  ---  ---  ---
+            "#]],
+        );
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16, u8);
+fn main() {
+    let S(1, .., 1, $0, 2);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16, u8)
+                          ---  ---  ---  ^^^  --
+            "#]],
+        );
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16);
+fn main() {
+    let S(1, $0.., 1);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16)
+                          ---  ^^^  ---  ---
+            "#]],
+        );
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32, f32, u16);
+fn main() {
+    let S(1, ..$0, 1);
+}
+"#,
+            expect![[r#"
+                A cool tuple struct
+                ------
+                struct S (u32, i32, f32, u16)
+                          ---  ^^^  ---  ---
+            "#]],
+        );
+    }
+
     #[test]
     fn generic_struct() {
         check(

crates/parser/src/grammar/patterns.rs

@@ -431,14 +431,15 @@ fn slice_pat(p: &mut Parser<'_>) -> CompletedMarker {
 
 fn pat_list(p: &mut Parser<'_>, ket: SyntaxKind) {
     while !p.at(EOF) && !p.at(ket) {
-        if !p.at_ts(PAT_TOP_FIRST) {
-            p.error("expected a pattern");
-            break;
-        }
-
         pattern_top(p);
-        if !p.at(ket) {
+        if !p.at(T![,]) {
-            p.expect(T![,]);
+            if p.at_ts(PAT_TOP_FIRST) {
+                p.error(format!("expected {:?}, got {:?}", T![,], p.current()));
+            } else {
+                break;
+            }
+        } else {
+            p.bump(T![,]);
         }
     }
 }