Automatically add semicolon when completing unit-returning functions

But provide a config to suppress that.

I didn't check whether we are in statement expression position, because this is hard in completion (due to the natural incompleteness of source code when completion is invoked), and anyway using function returning unit as an argument to something seems... dubious.

crates/ide-completion/src/completions/dot.rs

@@ -600,7 +600,7 @@ fn foo(a: A) { a.$0 }
 struct A {}
 trait Trait { fn the_method(&self); }
 impl Trait for A {}
-fn foo(a: A) { a.the_method()$0 }
+fn foo(a: A) { a.the_method();$0 }
 "#,
         );
     }

crates/ide-completion/src/config.rs

@@ -19,6 +19,7 @@ pub struct CompletionConfig {
     pub term_search_fuel: u64,
     pub full_function_signatures: bool,
     pub callable: Option<CallableSnippets>,
+    pub add_semicolon_to_unit: bool,
     pub snippet_cap: Option<SnippetCap>,
     pub insert_use: InsertUseConfig,
     pub prefer_no_std: bool,

crates/ide-completion/src/render.rs

@@ -1185,7 +1185,7 @@ fn main() { fo$0 }
                         label: "main()",
                         source_range: 68..70,
                         delete: 68..70,
-                        insert: "main()$0",
+                        insert: "main();$0",
                         kind: SymbolKind(
                             Function,
                         ),
@@ -1244,7 +1244,7 @@ fn main() { let _: m::Spam = S$0 }
                         label: "main()",
                         source_range: 75..76,
                         delete: 75..76,
-                        insert: "main()$0",
+                        insert: "main();$0",
                         kind: SymbolKind(
                             Function,
                         ),
@@ -1331,7 +1331,7 @@ fn main() { som$0 }
                         label: "main()",
                         source_range: 56..59,
                         delete: 56..59,
-                        insert: "main()$0",
+                        insert: "main();$0",
                         kind: SymbolKind(
                             Function,
                         ),
@@ -1342,7 +1342,7 @@ fn main() { som$0 }
                         label: "something_deprecated()",
                         source_range: 56..59,
                         delete: 56..59,
-                        insert: "something_deprecated()$0",
+                        insert: "something_deprecated();$0",
                         kind: SymbolKind(
                             Function,
                         ),
@@ -1413,7 +1413,7 @@ impl S {
                         label: "bar()",
                         source_range: 94..94,
                         delete: 94..94,
-                        insert: "bar()$0",
+                        insert: "bar();$0",
                         kind: SymbolKind(
                             Method,
                         ),
@@ -1540,7 +1540,7 @@ fn foo(s: S) { s.$0 }
                         label: "the_method()",
                         source_range: 81..81,
                         delete: 81..81,
-                        insert: "the_method()$0",
+                        insert: "the_method();$0",
                         kind: SymbolKind(
                             Method,
                         ),
@@ -2789,7 +2789,7 @@ fn main() {
             r#"
 mod m { pub fn r#type {} }
 fn main() {
-    m::r#type()$0
+    m::r#type();$0
 }
 "#,
         )
@@ -2963,7 +2963,7 @@ fn main() {
                         label: "flush()",
                         source_range: 193..193,
                         delete: 193..193,
-                        insert: "flush()$0",
+                        insert: "flush();$0",
                         kind: SymbolKind(
                             Method,
                         ),
@@ -2990,7 +2990,7 @@ fn main() {
                         label: "write()",
                         source_range: 193..193,
                         delete: 193..193,
-                        insert: "write()$0",
+                        insert: "write();$0",
                         kind: SymbolKind(
                             Method,
                         ),

crates/ide-completion/src/render/function.rs

@@ -1,10 +1,12 @@
 //! Renderer for function calls.
 
+use std::ops::ControlFlow;
+
 use hir::{db::HirDatabase, AsAssocItem, HirDisplay};
 use ide_db::{SnippetCap, SymbolKind};
 use itertools::Itertools;
 use stdx::{format_to, to_lower_snake_case};
-use syntax::{format_smolstr, AstNode, Edition, SmolStr, ToSmolStr};
+use syntax::{ast, format_smolstr, AstNode, Edition, SmolStr, SyntaxKind, ToSmolStr, T};
 
 use crate::{
     context::{CompletionContext, DotAccess, DotAccessKind, PathCompletionCtx, PathKind},
@@ -160,7 +162,16 @@ fn render(
         .lookup_by(name.unescaped().display(db).to_smolstr());
 
     if let Some((cap, (self_param, params))) = complete_call_parens {
-        add_call_parens(&mut item, completion, cap, call, escaped_call, self_param, params);
+        add_call_parens(
+            &mut item,
+            completion,
+            cap,
+            call,
+            escaped_call,
+            self_param,
+            params,
+            &ret_type,
+        );
     }
 
     match ctx.import_to_add {
@@ -217,10 +228,11 @@ pub(super) fn add_call_parens<'b>(
     escaped_name: SmolStr,
     self_param: Option<hir::SelfParam>,
     params: Vec<hir::Param>,
+    ret_type: &hir::Type,
 ) -> &'b mut Builder {
     cov_mark::hit!(inserts_parens_for_function_calls);
 
-    let (snippet, label_suffix) = if self_param.is_none() && params.is_empty() {
+    let (mut snippet, label_suffix) = if self_param.is_none() && params.is_empty() {
         (format!("{escaped_name}()$0"), "()")
     } else {
         builder.trigger_call_info();
@@ -265,6 +277,35 @@ pub(super) fn add_call_parens<'b>(
 
         (snippet, "(…)")
     };
+    if ret_type.is_unit() && ctx.config.add_semicolon_to_unit {
+        let next_non_trivia_token =
+            std::iter::successors(ctx.token.next_token(), |it| it.next_token())
+                .find(|it| !it.kind().is_trivia());
+        let in_match_arm = ctx.token.parent_ancestors().try_for_each(|ancestor| {
+            if ast::MatchArm::can_cast(ancestor.kind()) {
+                ControlFlow::Break(true)
+            } else if matches!(ancestor.kind(), SyntaxKind::EXPR_STMT | SyntaxKind::BLOCK_EXPR) {
+                ControlFlow::Break(false)
+            } else {
+                ControlFlow::Continue(())
+            }
+        });
+        // FIXME: This will assume expr macros are not inside match, we need to somehow go to the "parent" of the root node.
+        let in_match_arm = match in_match_arm {
+            ControlFlow::Continue(()) => false,
+            ControlFlow::Break(it) => it,
+        };
+        let complete_token = if in_match_arm { T![,] } else { T![;] };
+        if next_non_trivia_token.map(|it| it.kind()) != Some(complete_token) {
+            cov_mark::hit!(complete_semicolon);
+            let ch = if in_match_arm { ',' } else { ';' };
+            if snippet.ends_with("$0") {
+                snippet.insert(snippet.len() - "$0".len(), ch);
+            } else {
+                snippet.push(ch);
+            }
+        }
+    }
     builder.label(SmolStr::from_iter([&name, label_suffix])).insert_snippet(cap, snippet)
 }
 
@@ -393,7 +434,7 @@ fn main() { no_$0 }
 "#,
             r#"
 fn no_args() {}
-fn main() { no_args()$0 }
+fn main() { no_args();$0 }
 "#,
         );
 
@@ -405,7 +446,7 @@ fn main() { with_$0 }
 "#,
             r#"
 fn with_args(x: i32, y: String) {}
-fn main() { with_args(${1:x}, ${2:y})$0 }
+fn main() { with_args(${1:x}, ${2:y});$0 }
 "#,
         );
 
@@ -414,14 +455,14 @@ fn main() { with_args(${1:x}, ${2:y})$0 }
             r#"
 struct S;
 impl S {
-    fn foo(&self) {}
+    fn foo(&self) -> i32 { 0 }
 }
 fn bar(s: &S) { s.f$0 }
 "#,
             r#"
 struct S;
 impl S {
-    fn foo(&self) {}
+    fn foo(&self) -> i32 { 0 }
 }
 fn bar(s: &S) { s.foo()$0 }
 "#,
@@ -444,7 +485,7 @@ impl S {
     fn foo(&self, x: i32) {}
 }
 fn bar(s: &S) {
-    s.foo(${1:x})$0
+    s.foo(${1:x});$0
 }
 "#,
         );
@@ -463,7 +504,7 @@ impl S {
 struct S {}
 impl S {
     fn foo(&self, x: i32) {
-        self.foo(${1:x})$0
+        self.foo(${1:x});$0
     }
 }
 "#,
@@ -486,7 +527,7 @@ struct S;
 impl S {
     fn foo(&self) {}
 }
-fn main() { S::foo(${1:&self})$0 }
+fn main() { S::foo(${1:&self});$0 }
 "#,
         );
     }
@@ -503,7 +544,7 @@ fn main() { with_$0 }
 "#,
             r#"
 fn with_args(x: i32, y: String) {}
-fn main() { with_args($0) }
+fn main() { with_args($0); }
 "#,
         );
     }
@@ -518,7 +559,7 @@ fn main() { f$0 }
 "#,
             r#"
 fn foo(_foo: i32, ___bar: bool, ho_ge_: String) {}
-fn main() { foo(${1:foo}, ${2:bar}, ${3:ho_ge_})$0 }
+fn main() { foo(${1:foo}, ${2:bar}, ${3:ho_ge_});$0 }
 "#,
         );
     }
@@ -540,7 +581,7 @@ struct Foo {}
 fn ref_arg(x: &Foo) {}
 fn main() {
     let x = Foo {};
-    ref_arg(${1:&x})$0
+    ref_arg(${1:&x});$0
 }
 "#,
         );
@@ -563,7 +604,7 @@ struct Foo {}
 fn ref_arg(x: &mut Foo) {}
 fn main() {
     let x = Foo {};
-    ref_arg(${1:&mut x})$0
+    ref_arg(${1:&mut x});$0
 }
 "#,
         );
@@ -596,7 +637,7 @@ impl Bar {
 fn main() {
     let x = Foo {};
     let y = Bar {};
-    y.apply_foo(${1:&x})$0
+    y.apply_foo(${1:&x});$0
 }
 "#,
         );
@@ -617,7 +658,7 @@ fn main() {
 fn take_mutably(mut x: &i32) {}
 
 fn main() {
-    take_mutably(${1:x})$0
+    take_mutably(${1:x});$0
 }
 "#,
         );
@@ -650,7 +691,7 @@ fn qux(Foo { bar }: Foo) {
 }
 
 fn main() {
-  qux(${1:foo})$0
+  qux(${1:foo});$0
 }
 "#,
         );
@@ -736,6 +777,115 @@ fn g(foo: ()#[baz = "qux"] mut ba$0)
             r#"
 fn f(foo: (), #[baz = "qux"] mut bar: u32) {}
 fn g(foo: (), #[baz = "qux"] mut bar: u32)
+"#,
+        );
+    }
+
+    #[test]
+    fn complete_semicolon_for_unit() {
+        cov_mark::check!(complete_semicolon);
+        check_edit(
+            r#"foo"#,
+            r#"
+fn foo() {}
+fn bar() {
+    foo$0
+}
+"#,
+            r#"
+fn foo() {}
+fn bar() {
+    foo();$0
+}
+"#,
+        );
+        check_edit(
+            r#"foo"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo$0
+}
+"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo(${1:a});$0
+}
+"#,
+        );
+        check_edit(
+            r#"foo"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo$0;
+}
+"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo(${1:a})$0;
+}
+"#,
+        );
+        check_edit_with_config(
+            CompletionConfig { add_semicolon_to_unit: false, ..TEST_CONFIG },
+            r#"foo"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo$0
+}
+"#,
+            r#"
+fn foo(a: i32) {}
+fn bar() {
+    foo(${1:a})$0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn complete_comma_for_unit_match_arm() {
+        cov_mark::check!(complete_semicolon);
+        check_edit(
+            r#"foo"#,
+            r#"
+fn foo() {}
+fn bar() {
+    match Some(false) {
+        v => fo$0
+    }
+}
+"#,
+            r#"
+fn foo() {}
+fn bar() {
+    match Some(false) {
+        v => foo(),$0
+    }
+}
+"#,
+        );
+        check_edit(
+            r#"foo"#,
+            r#"
+fn foo() {}
+fn bar() {
+    match Some(false) {
+        v => fo$0,
+    }
+}
+"#,
+            r#"
+fn foo() {}
+fn bar() {
+    match Some(false) {
+        v => foo()$0,
+    }
+}
 "#,
         );
     }

crates/ide-completion/src/tests.rs

@@ -70,6 +70,7 @@ pub(crate) const TEST_CONFIG: CompletionConfig = CompletionConfig {
     term_search_fuel: 200,
     full_function_signatures: false,
     callable: Some(CallableSnippets::FillArguments),
+    add_semicolon_to_unit: true,
     snippet_cap: SnippetCap::new(true),
     insert_use: InsertUseConfig {
         granularity: ImportGranularity::Crate,

crates/ide-completion/src/tests/flyimport.rs

@@ -53,7 +53,7 @@ fn main() {
 use dep::io::stdin;
 
 fn main() {
-    stdin()$0
+    stdin();$0
 }
 "#,
     );
@@ -274,7 +274,7 @@ fn trait_function_fuzzy_completion() {
 use dep::test_mod::TestTrait;
 
 fn main() {
-    dep::test_mod::TestStruct::weird_function()$0
+    dep::test_mod::TestStruct::weird_function();$0
 }
 "#,
     );
@@ -368,7 +368,7 @@ use dep::test_mod::TestTrait;
 
 fn main() {
     let test_struct = dep::test_mod::TestStruct {};
-    test_struct.random_method()$0
+    test_struct.random_method();$0
 }
 "#,
     );
@@ -419,7 +419,7 @@ impl foo::TestTrait for fundamental::Box<TestStruct> {
 
 fn main() {
     let t = fundamental::Box(TestStruct);
-    t.some_method()$0
+    t.some_method();$0
 }
 "#,
     );
@@ -466,7 +466,7 @@ impl foo::TestTrait for &TestStruct {
 
 fn main() {
     let t = &TestStruct;
-    t.some_method()$0
+    t.some_method();$0
 }
 "#,
     );
@@ -507,7 +507,7 @@ fn completion<T: Wrapper>(whatever: T) {
 use foo::{NotInScope, Wrapper};
 
 fn completion<T: Wrapper>(whatever: T) {
-    whatever.inner().not_in_scope()$0
+    whatever.inner().not_in_scope();$0
 }
 "#,
     );
@@ -579,7 +579,7 @@ fn main() {
 use dep::test_mod::TestTrait;
 
 fn main() {
-    dep::test_mod::TestAlias::random_method()$0
+    dep::test_mod::TestAlias::random_method();$0
 }
 "#,
     );
@@ -702,7 +702,7 @@ fn main() {
 use dep::test_mod::TestTrait;
 
 fn main() {
-    dep::test_mod::TestStruct::another_function()$0
+    dep::test_mod::TestStruct::another_function();$0
 }
 "#,
     );

crates/ide-completion/src/tests/raw_identifiers.rs

@@ -30,7 +30,7 @@ fn foo() {
 "#,
         expect![[r#"
             fn foo() {
-                a::dyn()$0
+                a::dyn();$0
         "#]],
     );
 
@@ -45,7 +45,7 @@ fn foo() {
 "#,
         expect![[r#"
             fn foo() {
-                a::dyn()$0
+                a::dyn();$0
         "#]],
     );
 }
@@ -63,7 +63,7 @@ fn foo() {
 "#,
         expect![[r#"
             fn foo() {
-                a::r#dyn()$0
+                a::r#dyn();$0
         "#]],
     );
 
@@ -78,7 +78,7 @@ fn foo() {
 "#,
         expect![[r#"
             fn foo() {
-                a::r#dyn()$0
+                a::r#dyn();$0
         "#]],
     );
 }

crates/ide-completion/src/tests/special.rs

@@ -63,7 +63,7 @@ fn _alpha() {}
 "#,
         r#"
 fn main() {
-    _alpha()$0
+    _alpha();$0
 }
 fn _alpha() {}
 "#,

crates/rust-analyzer/src/config.rs

@@ -420,6 +420,10 @@ config_data! {
         assist_termSearch_fuel: usize = 1800,
 
 
+        /// Whether to automatically add a semicolon when completing unit-returning functions.
+        ///
+        /// In `match` arms it completes a comma instead.
+        completion_addSemicolonToUnit: bool = true,
         /// Toggles the additional completions that automatically add imports when completed.
         /// Note that your client must specify the `additionalTextEdits` LSP client capability to truly have this feature enabled.
         completion_autoimport_enable: bool       = true,
@@ -1441,6 +1445,7 @@ impl Config {
                 CallableCompletionDef::AddParentheses => Some(CallableSnippets::AddParentheses),
                 CallableCompletionDef::None => None,
             },
+            add_semicolon_to_unit: *self.completion_addSemicolonToUnit(source_root),
             snippet_cap: SnippetCap::new(self.completion_snippet()),
             insert_use: self.insert_use_config(source_root),
             prefer_no_std: self.imports_preferNoStd(source_root).to_owned(),

crates/rust-analyzer/src/integrated_benchmarks.rs

@@ -167,6 +167,7 @@ fn integrated_completion_benchmark() {
             prefer_absolute: false,
             snippets: Vec::new(),
             limit: None,
+            add_semicolon_to_unit: true,
         };
         let position =
             FilePosition { file_id, offset: TextSize::try_from(completion_offset).unwrap() };
@@ -213,6 +214,7 @@ fn integrated_completion_benchmark() {
             prefer_absolute: false,
             snippets: Vec::new(),
             limit: None,
+            add_semicolon_to_unit: true,
         };
         let position =
             FilePosition { file_id, offset: TextSize::try_from(completion_offset).unwrap() };
@@ -257,6 +259,7 @@ fn integrated_completion_benchmark() {
             prefer_absolute: false,
             snippets: Vec::new(),
             limit: None,
+            add_semicolon_to_unit: true,
         };
         let position =
             FilePosition { file_id, offset: TextSize::try_from(completion_offset).unwrap() };

docs/user/generated_config.adoc

@@ -261,6 +261,13 @@ Aliased as `"checkOnSave.targets"`.
 Whether `--workspace` should be passed to `cargo check`.
 If false, `-p <package>` will be passed instead.
 --
+[[rust-analyzer.completion.addSemicolonToUnit]]rust-analyzer.completion.addSemicolonToUnit (default: `true`)::
++
+--
+Whether to automatically add a semicolon when completing unit-returning functions.
+
+In `match` arms it completes a comma instead.
+--
 [[rust-analyzer.completion.autoimport.enable]]rust-analyzer.completion.autoimport.enable (default: `true`)::
 +
 --

editors/code/package.json

@@ -1027,6 +1027,16 @@
                     }
                 }
             },
+            {
+                "title": "completion",
+                "properties": {
+                    "rust-analyzer.completion.addSemicolonToUnit": {
+                        "markdownDescription": "Whether to automatically add a semicolon when completing unit-returning functions.\n\nIn `match` arms it completes a comma instead.",
+                        "default": true,
+                        "type": "boolean"
+                    }
+                }
+            },
             {
                 "title": "completion",
                 "properties": {