Fix incorrect precedence caused by range expression

compiler/rustc_hir_typeck/src/expr.rs

@@ -77,6 +77,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             }
             false
         };
+
+        // Special case: range expressions are desugared to struct literals in HIR,
+        // so they would normally return `Unambiguous` precedence in expr.precedence.
+        // we should return `Range` precedence for correct parenthesization in suggestions.
+        if is_range_literal(expr) {
+            return ExprPrecedence::Range;
+        }
+
         expr.precedence(&has_attr)
     }
 

tests/ui/feature-gates/feature-gate-new_range.stderr

@@ -10,8 +10,8 @@ LL |     let a: core::range::RangeFrom<u8> = 1..;
               found struct `std::ops::RangeFrom<{integer}>`
 help: call `Into::into` on this expression to convert `std::ops::RangeFrom<{integer}>` into `std::range::RangeFrom<u8>`
    |
-LL |     let a: core::range::RangeFrom<u8> = 1...into();
-   |                                            +++++++
+LL |     let a: core::range::RangeFrom<u8> = (1..).into();
+   |                                         +   ++++++++
 
 error[E0308]: mismatched types
   --> $DIR/feature-gate-new_range.rs:6:37
@@ -25,8 +25,8 @@ LL |     let b: core::range::Range<u8> = 2..3;
               found struct `std::ops::Range<{integer}>`
 help: call `Into::into` on this expression to convert `std::ops::Range<{integer}>` into `std::range::Range<u8>`
    |
-LL |     let b: core::range::Range<u8> = 2..3.into();
-   |                                         +++++++
+LL |     let b: core::range::Range<u8> = (2..3).into();
+   |                                     +    ++++++++
 
 error[E0308]: mismatched types
   --> $DIR/feature-gate-new_range.rs:8:46
@@ -40,8 +40,8 @@ LL |     let c: core::range::RangeInclusive<u8> = 4..=5;
               found struct `std::ops::RangeInclusive<{integer}>`
 help: call `Into::into` on this expression to convert `std::ops::RangeInclusive<{integer}>` into `std::range::RangeInclusive<u8>`
    |
-LL |     let c: core::range::RangeInclusive<u8> = 4..=5.into();
-   |                                                   +++++++
+LL |     let c: core::range::RangeInclusive<u8> = (4..=5).into();
+   |                                              +     ++++++++
 
 error: aborting due to 3 previous errors
 

tests/ui/suggestions/into-convert-range-issue-148344.fixed

@@ -0,0 +1,15 @@
+//@ run-rustfix
+use std::ops::Range;
+
+struct Strange;
+impl From<Range<usize>> for Strange {
+    fn from(_: Range<usize>) -> Self {
+        Self
+    }
+}
+
+fn main() {
+    let _: Strange = (0..10).into();
+    //~^ ERROR mismatched types
+    //~| HELP call `Into::into` on this expression
+}

tests/ui/suggestions/into-convert-range-issue-148344.rs

@@ -0,0 +1,15 @@
+//@ run-rustfix
+use std::ops::Range;
+
+struct Strange;
+impl From<Range<usize>> for Strange {
+    fn from(_: Range<usize>) -> Self {
+        Self
+    }
+}
+
+fn main() {
+    let _: Strange = 0..10;
+    //~^ ERROR mismatched types
+    //~| HELP call `Into::into` on this expression
+}

tests/ui/suggestions/into-convert-range-issue-148344.stderr

@@ -0,0 +1,18 @@
+error[E0308]: mismatched types
+  --> $DIR/into-convert-range-issue-148344.rs:12:22
+   |
+LL |     let _: Strange = 0..10;
+   |            -------   ^^^^^ expected `Strange`, found `Range<{integer}>`
+   |            |
+   |            expected due to this
+   |
+   = note: expected struct `Strange`
+              found struct `std::ops::Range<{integer}>`
+help: call `Into::into` on this expression to convert `std::ops::Range<{integer}>` into `Strange`
+   |
+LL |     let _: Strange = (0..10).into();
+   |                      +     ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.