1 files changed, 221 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs
new file mode 100644
index 000000000..e9c7c6bae
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs
@@ -0,0 +1,221 @@
+use syntax::{ast, AstNode};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: remove_parentheses
+//
+// Removes redundant parentheses.
+//
+// ```
+// fn main() {
+//     _ = $0(2) + 2;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     _ = 2 + 2;
+// }
+// ```
+pub(crate) fn remove_parentheses(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let parens = ctx.find_node_at_offset::<ast::ParenExpr>()?;
+
+    let cursor_in_range =
+        parens.l_paren_token()?.text_range().contains_range(ctx.selection_trimmed())
+            || parens.r_paren_token()?.text_range().contains_range(ctx.selection_trimmed());
+    if !cursor_in_range {
+        return None;
+    }
+
+    let expr = parens.expr()?;
+
+    let parent = parens.syntax().parent()?;
+    if expr.needs_parens_in(parent) {
+        return None;
+    }
+
+    let target = parens.syntax().text_range();
+    acc.add(
+        AssistId("remove_parentheses", AssistKind::Refactor),
+        "Remove redundant parentheses",
+        target,
+        |builder| builder.replace_ast(parens.into(), expr),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn remove_parens_simple() {
+        check_assist(remove_parentheses, r#"fn f() { $0(2) + 2; }"#, r#"fn f() { 2 + 2; }"#);
+        check_assist(remove_parentheses, r#"fn f() { ($02) + 2; }"#, r#"fn f() { 2 + 2; }"#);
+        check_assist(remove_parentheses, r#"fn f() { (2)$0 + 2; }"#, r#"fn f() { 2 + 2; }"#);
+        check_assist(remove_parentheses, r#"fn f() { (2$0) + 2; }"#, r#"fn f() { 2 + 2; }"#);
+    }
+
+    #[test]
+    fn remove_parens_closure() {
+        check_assist(remove_parentheses, r#"fn f() { &$0(|| 42) }"#, r#"fn f() { &|| 42 }"#);
+
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0(|| 42).f() }"#);
+    }
+
+    #[test]
+    fn remove_parens_if_let_chains() {
+        check_assist_not_applicable(
+            remove_parentheses,
+            r#"fn f() { if let true = $0(true && true) {} }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_associativity() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { $0(2 + 2) + 2; }"#,
+            r#"fn f() { 2 + 2 + 2; }"#,
+        );
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { 2 + $0(2 + 2); }"#);
+    }
+
+    #[test]
+    fn remove_parens_precedence() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { $0(2 * 3) + 1; }"#,
+            r#"fn f() { 2 * 3 + 1; }"#,
+        );
+        check_assist(remove_parentheses, r#"fn f() { ( $0(2) ); }"#, r#"fn f() { ( 2 ); }"#);
+        check_assist(remove_parentheses, r#"fn f() { $0(2?)?; }"#, r#"fn f() { 2??; }"#);
+        check_assist(remove_parentheses, r#"fn f() { f(($02 + 2)); }"#, r#"fn f() { f(2 + 2); }"#);
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { (1<2)&&$0(3>4); }"#,
+            r#"fn f() { (1<2)&&3>4; }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_doesnt_apply_precedence() {
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0(2 + 2) * 8; }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0(2 + 2).f(); }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0(2 + 2).await; }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0!(2..2); }"#);
+    }
+
+    #[test]
+    fn remove_parens_doesnt_apply_with_cursor_not_on_paren() {
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { (2 +$0 2) }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() {$0 (2 + 2) }"#);
+    }
+
+    #[test]
+    fn remove_parens_doesnt_apply_when_expr_would_be_turned_into_a_statement() {
+        check_assist_not_applicable(remove_parentheses, r#"fn x() -> u8 { $0({ 0 } + 1) }"#);
+        check_assist_not_applicable(
+            remove_parentheses,
+            r#"fn x() -> u8 { $0(if true { 0 } else { 1 } + 1) }"#,
+        );
+        check_assist_not_applicable(remove_parentheses, r#"fn x() -> u8 { $0(loop {} + 1) }"#);
+    }
+
+    #[test]
+    fn remove_parens_doesnt_apply_weird_syntax_and_adge_cases() {
+        // removing `()` would break code because {} would be counted as the loop/if body
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { for _ in $0(0..{3}) {} }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { for _ in $0(S {}) {} }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { if $0(S {} == 2) {} }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { if $0(return) {} }"#);
+    }
+
+    #[test]
+    fn remove_parens_return_with_value_followed_by_block() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { if $0(return ()) {} }"#,
+            r#"fn f() { if return () {} }"#,
+        );
+    }
+
+    #[test]
+    fn remove_exprs_let_else_restrictions() {
+        // `}` is not allowed before `else` here
+        check_assist_not_applicable(
+            remove_parentheses,
+            r#"fn f() { let _ = $0(S{}) else { return }; }"#,
+        );
+
+        // logic operators can't directly appear in the let-else
+        check_assist_not_applicable(
+            remove_parentheses,
+            r#"fn f() { let _ = $0(false || false) else { return }; }"#,
+        );
+        check_assist_not_applicable(
+            remove_parentheses,
+            r#"fn f() { let _ = $0(true && true) else { return }; }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_weird_places() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { match () { _=>$0(()) } }"#,
+            r#"fn f() { match () { _=>() } }"#,
+        );
+
+        check_assist(
+            remove_parentheses,
+            r#"fn x() -> u8 { { [$0({ 0 } + 1)] } }"#,
+            r#"fn x() -> u8 { { [{ 0 } + 1] } }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_return_dot_f() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { $0(return).f() }"#,
+            r#"fn f() { return.f() }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_prefix_then_return_something() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { &$0(return ()) }"#,
+            r#"fn f() { &return () }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_double_paren_stmt() {
+        check_assist(
+            remove_parentheses,
+            r#"fn x() -> u8 { $0(({ 0 } + 1)) }"#,
+            r#"fn x() -> u8 { ({ 0 } + 1) }"#,
+        );
+
+        check_assist(
+            remove_parentheses,
+            r#"fn x() -> u8 { (($0{ 0 } + 1)) }"#,
+            r#"fn x() -> u8 { ({ 0 } + 1) }"#,
+        );
+    }
+
+    #[test]
+    fn remove_parens_im_tired_of_naming_tests() {
+        check_assist(
+            remove_parentheses,
+            r#"fn f() { 2 + $0(return 2) }"#,
+            r#"fn f() { 2 + return 2 }"#,
+        );
+
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { $0(return 2) + 2 }"#);
+    }
+}