Rollup merge of #125049 - dtolnay:castbrace, r=compiler-errors

Disallow cast with trailing braced macro in let-else

This fixes an edge case I noticed while porting #118880 and #119062 to syn.

Previously, rustc incorrectly accepted code such as:

```rust
let foo = &std::ptr::null as &'static dyn std::ops::Fn() -> *const primitive! {
    8
} else {
    return;
};
```

even though a right curl brace `}` directly before `else` in a `let...else` statement is not supposed to be valid syntax.

2 files changed, 101 insertions, 282 deletions

diff --git a/tests/ui/parser/bad-let-else-statement.rs b/tests/ui/parser/bad-let-else-statement.rs
index de41a07568f..ff6619cbc98 100644
--- a/tests/ui/parser/bad-let-else-statement.rs
+++ b/tests/ui/parser/bad-let-else-statement.rs
@@ -3,8 +3,7 @@
 #![feature(explicit_tail_calls)]
 
 fn a() {
-    let foo = {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = {
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -22,8 +21,7 @@ fn b() {
 }
 
 fn c() {
-    let foo = if true {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = if true {
         1
     } else {
         0
@@ -43,8 +41,7 @@ fn d() {
 }
 
 fn e() {
-    let foo = match true {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = match true {
         true => 1,
         false => 0
     } else {
@@ -53,10 +50,12 @@ fn e() {
     };
 }
 
-struct X {a: i32}
 fn f() {
-    let foo = X {
-        //~^ WARN irrefutable `let...else` pattern
+    struct X {
+        a: i32,
+    }
+
+    let X { a: 0 } = X {
         a: 1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -74,8 +73,7 @@ fn g() {
 }
 
 fn h() {
-    let foo = const {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = const {
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -84,8 +82,7 @@ fn h() {
 }
 
 fn i() {
-    let foo = &{
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = &{
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -94,8 +91,8 @@ fn i() {
 }
 
 fn j() {
-    let bar = 0;
-    let foo = bar = { //~ ERROR: cannot assign twice
+    let mut bar = 0;
+    let foo = bar = {
         //~^ WARN irrefutable `let...else` pattern
         1
     } else {
@@ -105,8 +102,7 @@ fn j() {
 }
 
 fn k() {
-    let foo = 1 + {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = 1 + {
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -115,8 +111,8 @@ fn k() {
 }
 
 fn l() {
-    let foo = 1..{
-        //~^ WARN irrefutable `let...else` pattern
+    const RANGE: std::ops::Range<u8> = 0..0;
+    let RANGE = 1..{
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -125,8 +121,7 @@ fn l() {
 }
 
 fn m() {
-    let foo = return {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = return {
         ()
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -135,8 +130,7 @@ fn m() {
 }
 
 fn n() {
-    let foo = -{
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = -{
         1
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -145,8 +139,7 @@ fn n() {
 }
 
 fn o() -> Result<(), ()> {
-    let foo = do yeet {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = do yeet {
         ()
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -155,8 +148,7 @@ fn o() -> Result<(), ()> {
 }
 
 fn p() {
-    let foo = become {
-        //~^ WARN irrefutable `let...else` pattern
+    let 0 = become {
         ()
     } else {
         //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
@@ -185,22 +177,37 @@ fn r() {
 
 fn s() {
     macro_rules! a {
-        () => { {} }
-        //~^ WARN irrefutable `let...else` pattern
-        //~| WARN irrefutable `let...else` pattern
+        () => {
+            { 1 }
+        };
     }
 
     macro_rules! b {
         (1) => {
-            let x = a!() else { return; };
+            let 0 = a!() else { return; };
         };
         (2) => {
-            let x = a! {} else { return; };
+            let 0 = a! {} else { return; };
             //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
         };
     }
 
-    b!(1); b!(2);
+    b!(1);
+    b!(2);
+}
+
+fn t() {
+    macro_rules! primitive {
+        (8) => { u8 };
+    }
+
+    let foo = &std::ptr::null as &'static dyn std::ops::Fn() -> *const primitive! {
+        //~^ WARN irrefutable `let...else` pattern
+        8
+    } else {
+        //~^ ERROR right curly brace `}` before `else` in a `let...else` statement not allowed
+        return;
+    };
 }
 
 fn main() {}
diff --git a/tests/ui/parser/bad-let-else-statement.stderr b/tests/ui/parser/bad-let-else-statement.stderr
index 3f7e176b3e3..0bf6a346dfb 100644
--- a/tests/ui/parser/bad-let-else-statement.stderr
+++ b/tests/ui/parser/bad-let-else-statement.stderr
@@ -1,19 +1,18 @@
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:9:5
+  --> $DIR/bad-let-else-statement.rs:8:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = ({
-LL |
+LL ~     let 0 = ({
 LL |         1
 LL ~     }) else {
    |
 
 error: `for...else` loops are not supported
-  --> $DIR/bad-let-else-statement.rs:18:7
+  --> $DIR/bad-let-else-statement.rs:17:7
    |
 LL |       let foo = for i in 1..2 {
    |                 --- `else` is attached to this loop
@@ -28,22 +27,22 @@ LL | |     };
    = note: consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:30:5
+  --> $DIR/bad-let-else-statement.rs:28:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = (if true {
-LL |
- ...
+LL ~     let 0 = (if true {
+LL |         1
+LL |     } else {
 LL |         0
 LL ~     }) else {
    |
 
 error: `loop...else` loops are not supported
-  --> $DIR/bad-let-else-statement.rs:39:7
+  --> $DIR/bad-let-else-statement.rs:37:7
    |
 LL |       let foo = loop {
    |                 ---- `else` is attached to this loop
@@ -58,36 +57,34 @@ LL | |     };
    = note: consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:50:5
+  --> $DIR/bad-let-else-statement.rs:47:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = (match true {
-LL |
+LL ~     let 0 = (match true {
 LL |         true => 1,
 LL |         false => 0
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:61:5
+  --> $DIR/bad-let-else-statement.rs:60:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = (X {
-LL |
+LL ~     let X { a: 0 } = (X {
 LL |         a: 1
 LL ~     }) else {
    |
 
 error: `while...else` loops are not supported
-  --> $DIR/bad-let-else-statement.rs:70:7
+  --> $DIR/bad-let-else-statement.rs:69:7
    |
 LL |       let foo = while false {
    |                 ----- `else` is attached to this loop
@@ -102,35 +99,33 @@ LL | |     };
    = note: consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:80:5
+  --> $DIR/bad-let-else-statement.rs:78:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = (const {
-LL |
+LL ~     let 0 = (const {
 LL |         1
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:90:5
+  --> $DIR/bad-let-else-statement.rs:87:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = &({
-LL |
+LL ~     let 0 = &({
 LL |         1
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:101:5
+  --> $DIR/bad-let-else-statement.rs:98:5
    |
 LL |     } else {
    |     ^
@@ -144,91 +139,85 @@ LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:111:5
+  --> $DIR/bad-let-else-statement.rs:107:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = 1 + ({
-LL |
+LL ~     let 0 = 1 + ({
 LL |         1
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:121:5
+  --> $DIR/bad-let-else-statement.rs:117:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = 1..({
-LL |
+LL ~     let RANGE = 1..({
 LL |         1
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:131:5
+  --> $DIR/bad-let-else-statement.rs:126:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = return ({
-LL |
+LL ~     let 0 = return ({
 LL |         ()
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:141:5
+  --> $DIR/bad-let-else-statement.rs:135:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = -({
-LL |
+LL ~     let 0 = -({
 LL |         1
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:151:5
+  --> $DIR/bad-let-else-statement.rs:144:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = do yeet ({
-LL |
+LL ~     let 0 = do yeet ({
 LL |         ()
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:161:5
+  --> $DIR/bad-let-else-statement.rs:153:5
    |
 LL |     } else {
    |     ^
    |
 help: wrap the expression in parentheses
    |
-LL ~     let foo = become ({
-LL |
+LL ~     let 0 = become ({
 LL |         ()
 LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:171:5
+  --> $DIR/bad-let-else-statement.rs:163:5
    |
 LL |     } else {
    |     ^
@@ -242,7 +231,7 @@ LL ~     }) else {
    |
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:181:31
+  --> $DIR/bad-let-else-statement.rs:173:31
    |
 LL |     let bad = format_args! {""} else { return; };
    |                               ^
@@ -253,98 +242,36 @@ LL |     let bad = format_args! ("") else { return; };
    |                            ~  ~
 
 error: right curly brace `}` before `else` in a `let...else` statement not allowed
-  --> $DIR/bad-let-else-statement.rs:198:25
+  --> $DIR/bad-let-else-statement.rs:207:5
    |
-LL |             let x = a! {} else { return; };
-   |                         ^
-...
-LL |     b!(1); b!(2);
-   |            ----- in this macro invocation
+LL |     } else {
+   |     ^
    |
-   = note: this error originates in the macro `b` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: use parentheses instead of braces for this macro
    |
-LL |             let x = a! () else { return; };
-   |                        ~~
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:6:5
-   |
-LL | /     let foo = {
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-   = note: `#[warn(irrefutable_let_patterns)]` on by default
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:25:5
-   |
-LL | /     let foo = if true {
-LL | |
-LL | |         1
-LL | |     } else {
-LL | |         0
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:46:5
-   |
-LL | /     let foo = match true {
-LL | |
-LL | |         true => 1,
-LL | |         false => 0
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:58:5
-   |
-LL | /     let foo = X {
-LL | |
-LL | |         a: 1
-LL | |     } else {
-   | |_____^
+LL ~     let foo = &std::ptr::null as &'static dyn std::ops::Fn() -> *const primitive! (
+LL |
+LL |         8
+LL ~     ) else {
    |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
 
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:77:5
-   |
-LL | /     let foo = const {
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
+error: right curly brace `}` before `else` in a `let...else` statement not allowed
+  --> $DIR/bad-let-else-statement.rs:190:25
    |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:87:5
+LL |             let 0 = a! {} else { return; };
+   |                         ^
+...
+LL |     b!(2);
+   |     ----- in this macro invocation
    |
-LL | /     let foo = &{
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
+   = note: this error originates in the macro `b` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: use parentheses instead of braces for this macro
    |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
+LL |             let 0 = a! () else { return; };
+   |                        ~~
 
 warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:98:5
+  --> $DIR/bad-let-else-statement.rs:95:5
    |
 LL | /     let foo = bar = {
 LL | |
@@ -354,96 +281,10 @@ LL | |     } else {
    |
    = note: this pattern will always match, so the `else` clause is useless
    = help: consider removing the `else` clause
-
-error[E0384]: cannot assign twice to immutable variable `bar`
-  --> $DIR/bad-let-else-statement.rs:98:15
-   |
-LL |       let bar = 0;
-   |           ---
-   |           |
-   |           first assignment to `bar`
-   |           help: consider making this binding mutable: `mut bar`
-LL |       let foo = bar = {
-   |  _______________^
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^ cannot assign twice to immutable variable
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:108:5
-   |
-LL | /     let foo = 1 + {
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:118:5
-   |
-LL | /     let foo = 1..{
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:128:5
-   |
-LL | /     let foo = return {
-LL | |
-LL | |         ()
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:138:5
-   |
-LL | /     let foo = -{
-LL | |
-LL | |         1
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:148:5
-   |
-LL | /     let foo = do yeet {
-LL | |
-LL | |         ()
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:158:5
-   |
-LL | /     let foo = become {
-LL | |
-LL | |         ()
-LL | |     } else {
-   | |_____^
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
+   = note: `#[warn(irrefutable_let_patterns)]` on by default
 
 warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:168:5
+  --> $DIR/bad-let-else-statement.rs:160:5
    |
 LL | /     let foo = |x: i32| {
 LL | |
@@ -455,7 +296,7 @@ LL | |     } else {
    = help: consider removing the `else` clause
 
 warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:178:5
+  --> $DIR/bad-let-else-statement.rs:170:5
    |
 LL |     let ok = format_args!("") else { return; };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -464,7 +305,7 @@ LL |     let ok = format_args!("") else { return; };
    = help: consider removing the `else` clause
 
 warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:181:5
+  --> $DIR/bad-let-else-statement.rs:173:5
    |
 LL |     let bad = format_args! {""} else { return; };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -473,45 +314,16 @@ LL |     let bad = format_args! {""} else { return; };
    = help: consider removing the `else` clause
 
 warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:188:19
-   |
-LL |           () => { {} }
-   |  ___________________^
-LL | |
-LL | |
-LL | |     }
-...  |
-LL | |         (1) => {
-LL | |             let x = a!() else { return; };
-   | |____________^
-...
-LL |       b!(1); b!(2);
-   |       ----- in this macro invocation
-   |
-   = note: this pattern will always match, so the `else` clause is useless
-   = help: consider removing the `else` clause
-   = note: this warning originates in the macro `b` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-warning: irrefutable `let...else` pattern
-  --> $DIR/bad-let-else-statement.rs:188:19
+  --> $DIR/bad-let-else-statement.rs:204:5
    |
-LL |           () => { {} }
-   |  ___________________^
-LL | |
+LL | /     let foo = &std::ptr::null as &'static dyn std::ops::Fn() -> *const primitive! {
 LL | |
-LL | |     }
-...  |
-LL | |         (2) => {
-LL | |             let x = a! {} else { return; };
-   | |____________^
-...
-LL |       b!(1); b!(2);
-   |              ----- in this macro invocation
+LL | |         8
+LL | |     } else {
+   | |_____^
    |
    = note: this pattern will always match, so the `else` clause is useless
    = help: consider removing the `else` clause
-   = note: this warning originates in the macro `b` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 20 previous errors; 18 warnings emitted
+error: aborting due to 20 previous errors; 5 warnings emitted
 
-For more information about this error, try `rustc --explain E0384`.