check double negation

compiler/rustc_parse/src/parser/expr.rs

@@ -284,6 +284,7 @@ impl<'a> Parser<'a> {
             if self.prev_token == token::BinOp(token::Minus)
                 && self.token == token::BinOp(token::Minus)
                 && self.prev_token.span.between(self.token.span).is_empty()
+                && !self.look_ahead(1, |tok| tok.can_begin_expr())
             {
                 let op_span = self.prev_token.span.to(self.token.span);
                 // Eat the second `-`
@@ -560,7 +561,10 @@ impl<'a> Parser<'a> {
             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)),
             // `~expr`
             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)),
-
+            // // `-expr`
+            // token::BinOp(token::Minus) => {
+            //     make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
+            // }
             // `*expr`
             token::BinOp(token::Star) => {
                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
@@ -604,17 +608,20 @@ impl<'a> Parser<'a> {
             }
             // Recover from `--x`:
             token::BinOp(token::Minus)
-                if this.look_ahead(1, |t| *t == token::BinOp(token::Minus)) =>
+                if this.look_ahead(1, |t| *t == token::BinOp(token::Minus))
+                    && !this.token.can_begin_expr() =>
             {
                 let starts_stmt = this.prev_token == token::Semi
                     || this.prev_token == token::CloseDelim(Delimiter::Brace);
                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
+                // if !this.token.can_begin_expr() {
                 // Eat both `-`s.
                 this.bump();
                 this.bump();
-
                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
                 this.recover_from_prefix_decrement(operand_expr, pre_span, starts_stmt)
+
+                // }
             }
             // `-expr`
             token::BinOp(token::Minus) => {

tests/ui/parser/issue-108495-dec-pass.rs

@@ -0,0 +1,48 @@
+// run-pass
+fn test1() {
+    let i = 0;
+    let c = i + --i;
+    println!("{c}");
+}
+fn test2() {
+    let i = 9;
+    let c = -- i + --i;
+    println!("{c}");
+}
+
+fn test3(){
+    let i=10;
+    println!("{}",i--i);
+}
+fn test4(){
+    let i=10;
+    println!("{}",--i);
+
+}
+struct Foo {
+    bar: Bar,
+}
+
+struct Bar {
+    qux: i32,
+}
+
+fn test5() {
+    let foo = Foo { bar: Bar { qux: 0 } };
+    let c=--foo.bar.qux;
+    println!("{c}");
+}
+
+fn test6(){
+    let x=2;
+    let y=--x;
+    println!("{y}");
+}
+fn main(){
+    test1();
+    test2();
+    test3();
+    test4();
+    test5();
+    test6();
+}

tests/ui/parser/issue-108495-dec.rs

@@ -1,18 +1,3 @@
-fn test1() {
-    let mut i = 0;
-    let _ = i + --i; //~ ERROR Rust has no prefix decrement operator
-}
-
-fn test2() {
-    let mut i = 0;
-    let _ = --i + i; //~ ERROR Rust has no prefix decrement operator
-}
-
-fn test3() {
-    let mut i = 0;
-    let _ = --i + --i; //~ ERROR Rust has no prefix decrement operator
-}
-
 fn test4() {
     let mut i = 0;
     let _ = i + i--; //~ ERROR Rust has no postfix decrement operator
@@ -21,32 +6,36 @@ fn test4() {
 
 fn test5() {
     let mut i = 0;
-    let _ = i-- + i; //~ ERROR Rust has no postfix decrement operator
+    let _ = i-- + i--; //~ ERROR Rust has no postfix decrement operator
 }
 
 fn test6() {
     let mut i = 0;
-    let _ = i-- + i--; //~ ERROR Rust has no postfix decrement operator
+    let _ = --i + i--; //~ ERROR Rust has no postfix decrement operator
 }
 
 fn test7() {
     let mut i = 0;
-    let _ = --i + i--; //~ ERROR Rust has no prefix decrement operator
+    let _ = i-- + --i; //~ ERROR Rust has no postfix decrement operator
 }
 
 fn test8() {
     let mut i = 0;
-    let _ = i-- + --i; //~ ERROR Rust has no postfix decrement operator
+    let _ = (1 + 2 + i)--; //~ ERROR Rust has no postfix decrement operator
 }
 
 fn test9() {
-    let mut i = 0;
-    let _ = (1 + 2 + i)--; //~ ERROR Rust has no postfix decrement operator
-}
-
-fn test10() {
     let mut i = 0;
     let _ = (i-- + 1) + 2; //~ ERROR Rust has no postfix decrement operator
 }
 
+
+
+fn test14(){
+    let i=10;
+    while i!=0{
+        i--; //~ ERROR Rust has no postfix decrement operator
+    }
+}
+
 fn main() { }

tests/ui/parser/issue-108495-dec.stderr

@@ -1,55 +1,11 @@
-error: Rust has no prefix decrement operator
-  --> $DIR/issue-dec.rs:3:17
-   |
-LL |     let _ = i + --i;
-   |                 ^^ not a valid prefix operator
-   |
-help: use `-= 1` instead
-   |
-LL |     let _ = i + { i -= 1; i };
-   |                 ~   +++++++++
-
-error: Rust has no prefix decrement operator
-  --> $DIR/issue-dec.rs:8:13
-   |
-LL |     let _ = --i + i;
-   |             ^^ not a valid prefix operator
-   |
-help: use `-= 1` instead
-   |
-LL |     let _ = { i -= 1; i } + i;
-   |             ~   +++++++++
-
-error: Rust has no prefix decrement operator
-  --> $DIR/issue-dec.rs:13:13
-   |
-LL |     let _ = --i + --i;
-   |             ^^ not a valid prefix operator
-   |
-help: use `-= 1` instead
-   |
-LL |     let _ = { i -= 1; i } + --i;
-   |             ~   +++++++++
-
 error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:18:18
+  --> $DIR/issue-108495-dec.rs:3:18
    |
 LL |     let _ = i + i--;
    |                  ^^ not a valid postfix operator
 
 error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:24:14
+  --> $DIR/issue-108495-dec.rs:9:14
-   |
-LL |     let _ = i-- + i;
-   |              ^^ not a valid postfix operator
-   |
-help: use `-= 1` instead
-   |
-LL |     let _ = { let tmp = i; i -= 1; tmp } + i;
-   |             +++++++++++  ~~~~~~~~~~~~~~~
-
-error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:29:14
    |
 LL |     let _ = i-- + i--;
    |              ^^ not a valid postfix operator
@@ -59,19 +15,14 @@ help: use `-= 1` instead
 LL |     let _ = { let tmp = i; i -= 1; tmp } + i--;
    |             +++++++++++  ~~~~~~~~~~~~~~~
 
-error: Rust has no prefix decrement operator
+error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:34:13
+  --> $DIR/issue-108495-dec.rs:14:20
    |
 LL |     let _ = --i + i--;
-   |             ^^ not a valid prefix operator
+   |                    ^^ not a valid postfix operator
-   |
-help: use `-= 1` instead
-   |
-LL |     let _ = { i -= 1; i } + i--;
-   |             ~   +++++++++
 
 error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:39:14
+  --> $DIR/issue-108495-dec.rs:19:14
    |
 LL |     let _ = i-- + --i;
    |              ^^ not a valid postfix operator
@@ -82,7 +33,7 @@ LL |     let _ = { let tmp = i; i -= 1; tmp } + --i;
    |             +++++++++++  ~~~~~~~~~~~~~~~
 
 error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:44:24
+  --> $DIR/issue-108495-dec.rs:24:24
    |
 LL |     let _ = (1 + 2 + i)--;
    |                        ^^ not a valid postfix operator
@@ -93,7 +44,7 @@ LL |     let _ = { let tmp = (1 + 2 + i); (1 + 2 + i) -= 1; tmp };
    |             +++++++++++            ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error: Rust has no postfix decrement operator
-  --> $DIR/issue-dec.rs:49:15
+  --> $DIR/issue-108495-dec.rs:29:15
    |
 LL |     let _ = (i-- + 1) + 2;
    |               ^^ not a valid postfix operator
@@ -103,5 +54,16 @@ help: use `-= 1` instead
 LL |     let _ = ({ let tmp = i; i -= 1; tmp } + 1) + 2;
    |              +++++++++++  ~~~~~~~~~~~~~~~
 
-error: aborting due to 10 previous errors
+error: Rust has no postfix decrement operator
+  --> $DIR/issue-108495-dec.rs:37:10
+   |
+LL |         i--;
+   |          ^^ not a valid postfix operator
+   |
+help: use `-= 1` instead
+   |
+LL |         i -= 1;
+   |           ~~~~
+
+error: aborting due to 7 previous errors