Do not suggest dereferencing in macro

Author: estebank

src/librustc_typeck/check/demand.rs

@@ -351,11 +351,14 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             if !self.infcx.type_moves_by_default(self.param_env,
                                                                 checked,
                                                                 sp) {
-                                let sp = cm.call_span_if_macro(sp);
-                                if let Ok(code) = cm.span_to_snippet(sp) {
-                                    return Some((sp,
-                                                 "consider dereferencing the borrow",
-                                                 format!("*{}", code)));
+                                // do not suggest if the span comes from a macro (#52783)
+                                if let (Ok(code),
+                                        true) = (cm.span_to_snippet(sp), sp == expr.span) {
+                                    return Some((
+                                        sp,
+                                        "consider dereferencing the borrow",
+                                        format!("*{}", code),
+                                    ));
                                 }
                             }
                         }

src/test/ui/deref-suggestion.rs

@@ -15,20 +15,26 @@ macro_rules! borrow {
 fn foo(_: String) {}
 
 fn foo2(s: &String) {
-    foo(s); //~ ERROR mismatched types
+    foo(s);
+    //~^ ERROR mismatched types
 }
 
 fn foo3(_: u32) {}
 fn foo4(u: &u32) {
-    foo3(u); //~ ERROR mismatched types
+    foo3(u);
+    //~^ ERROR mismatched types
 }
 
 fn main() {
     let s = String::new();
     let r_s = &s;
     foo2(r_s);
-    foo(&"aaa".to_owned()); //~ ERROR mismatched types
-    foo(&mut "aaa".to_owned()); //~ ERROR mismatched types
+    foo(&"aaa".to_owned());
+    //~^ ERROR mismatched types
+    foo(&mut "aaa".to_owned());
+    //~^ ERROR mismatched types
     foo3(borrow!(0));
     foo4(&0);
-}
+    assert_eq!(3i32, &3i32);
+    //~^ ERROR mismatched types
+}

src/test/ui/deref-suggestion.stderr

@@ -1,7 +1,7 @@
 error[E0308]: mismatched types
   --> $DIR/deref-suggestion.rs:18:9
    |
-LL |     foo(s); //~ ERROR mismatched types
+LL |     foo(s);
    |         ^
    |         |
    |         expected struct `std::string::String`, found reference
@@ -11,9 +11,9 @@ LL |     foo(s); //~ ERROR mismatched types
               found type `&std::string::String`
 
 error[E0308]: mismatched types
-  --> $DIR/deref-suggestion.rs:23:10
+  --> $DIR/deref-suggestion.rs:24:10
    |
-LL |     foo3(u); //~ ERROR mismatched types
+LL |     foo3(u);
    |          ^
    |          |
    |          expected u32, found &u32
@@ -23,9 +23,9 @@ LL |     foo3(u); //~ ERROR mismatched types
               found type `&u32`
 
 error[E0308]: mismatched types
-  --> $DIR/deref-suggestion.rs:30:9
+  --> $DIR/deref-suggestion.rs:32:9
    |
-LL |     foo(&"aaa".to_owned()); //~ ERROR mismatched types
+LL |     foo(&"aaa".to_owned());
    |         ^^^^^^^^^^^^^^^^^
    |         |
    |         expected struct `std::string::String`, found reference
@@ -35,9 +35,9 @@ LL |     foo(&"aaa".to_owned()); //~ ERROR mismatched types
               found type `&std::string::String`
 
 error[E0308]: mismatched types
-  --> $DIR/deref-suggestion.rs:31:9
+  --> $DIR/deref-suggestion.rs:34:9
    |
-LL |     foo(&mut "aaa".to_owned()); //~ ERROR mismatched types
+LL |     foo(&mut "aaa".to_owned());
    |         ^^^^^^^^^^^^^^^^^^^^^
    |         |
    |         expected struct `std::string::String`, found mutable reference
@@ -58,6 +58,16 @@ LL |     foo3(borrow!(0));
    = note: expected type `u32`
               found type `&{integer}`
 
-error: aborting due to 5 previous errors
+error[E0308]: mismatched types
+  --> $DIR/deref-suggestion.rs:38:5
+   |
+LL |     assert_eq!(3i32, &3i32);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^ expected i32, found &i32
+   |
+   = note: expected type `i32`
+              found type `&i32`
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0308`.