Rollup merge of rust-lang#85937 - m-ou-se:macro-ref-suggestions, r=estebank

Fix bad suggestions for code from proc_macro

Fixes rust-lang#85932

This disables these suggestions for spans from external macros, while keeping them for macros defined locally:

Before:
```
3 | #[hello]
  | ^^^^^^^^
  | |
  | expected `&mut i32`, found integer
  | help: consider mutably borrowing here: `&mut #[hello]`
```

After:
```
3 | #[hello]
  | ^^^^^^^^ expected `&mut i32`, found integer
```

Unchanged:
```
26 | macro_rules! bla { () => { x(123); } }
   |                              ^^^
   |                              |
   |                              expected `&mut i32`, found integer
   |                              help: consider mutably borrowing here: `&mut 123`
...
29 |     bla!();
   |     ------- in this macro invocation
```

Author: JohnTitor

compiler/rustc_typeck/src/check/demand.rs

@@ -8,6 +8,7 @@ use rustc_errors::{Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{is_range_literal, Node};
+use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::adjustment::AllowTwoPhase;
 use rustc_middle::ty::{self, AssocItem, Ty, TypeAndMut};
 use rustc_span::symbol::sym;
@@ -412,25 +413,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         checked_ty: Ty<'tcx>,
         expected: Ty<'tcx>,
     ) -> Option<(Span, &'static str, String, Applicability)> {
-        let sm = self.sess().source_map();
+        let sess = self.sess();
         let sp = expr.span;
-        if sm.is_imported(sp) {
-            // Ignore if span is from within a macro #41858, #58298. We previously used the macro
-            // call span, but that breaks down when the type error comes from multiple calls down.
+
+        // If the span is from an external macro, there's no suggestion we can make.
+        if in_external_macro(sess, sp) {
             return None;
         }
 
+        let sm = sess.source_map();
+
         let replace_prefix = |s: &str, old: &str, new: &str| {
             s.strip_prefix(old).map(|stripped| new.to_string() + stripped)
         };
 
         let is_struct_pat_shorthand_field =
             self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);
 
-        // If the span is from a macro, then it's hard to extract the text
-        // and make a good suggestion, so don't bother.
-        let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();
-
         // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
         let expr = expr.peel_drop_temps();
 
@@ -570,10 +569,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
                 _,
                 &ty::Ref(_, checked, _),
-            ) if {
-                self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
-            } =>
-            {
+            ) if self.infcx.can_sub(self.param_env, checked, &expected).is_ok() => {
                 // We have `&T`, check if what was expected was `T`. If so,
                 // we may want to suggest removing a `&`.
                 if sm.is_imported(expr.span) {
@@ -589,13 +585,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                     return None;
                 }
-                if let Ok(code) = sm.span_to_snippet(expr.span) {
-                    return Some((
-                        sp,
-                        "consider removing the borrow",
-                        code,
-                        Applicability::MachineApplicable,
-                    ));
+                if sp.contains(expr.span) {
+                    if let Ok(code) = sm.span_to_snippet(expr.span) {
+                        return Some((
+                            sp,
+                            "consider removing the borrow",
+                            code,
+                            Applicability::MachineApplicable,
+                        ));
+                    }
                 }
             }
             (
@@ -643,7 +641,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 }
             }
-            _ if sp == expr.span && !is_macro => {
+            _ if sp == expr.span => {
                 if let Some(steps) = self.deref_steps(checked_ty, expected) {
                     let expr = expr.peel_blocks();
 

src/test/ui/suggestions/auxiliary/proc-macro-type-error.rs

@@ -0,0 +1,18 @@
+// force-host
+// no-prefer-dynamic
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_quote)]
+
+extern crate proc_macro;
+
+use proc_macro::{quote, TokenStream};
+
+#[proc_macro_attribute]
+pub fn hello(_: TokenStream, _: TokenStream) -> TokenStream {
+    quote!(
+        fn f(_: &mut i32) {}
+        fn g() {
+            f(123);
+        }
+    )
+}

src/test/ui/suggestions/suggest-ref-macro.rs

@@ -0,0 +1,29 @@
+// run-check
+// aux-build:proc-macro-type-error.rs
+
+extern crate proc_macro_type_error;
+
+use proc_macro_type_error::hello;
+
+#[hello] //~ERROR mismatched types
+fn abc() {}
+
+fn x(_: &mut i32) {}
+
+macro_rules! bla {
+    () => {
+        x(123);
+        //~^ ERROR mismatched types
+        //~| SUGGESTION &mut 123
+    };
+    ($v:expr) => {
+        x($v)
+    }
+}
+
+fn main() {
+    bla!();
+    bla!(456);
+    //~^ ERROR mismatched types
+    //~| SUGGESTION &mut 456
+}

src/test/ui/suggestions/suggest-ref-macro.stderr

@@ -0,0 +1,34 @@
+error[E0308]: mismatched types
+  --> $DIR/suggest-ref-macro.rs:8:1
+   |
+LL | #[hello]
+   | ^^^^^^^^ expected `&mut i32`, found integer
+   |
+   = note: this error originates in the attribute macro `hello` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/suggest-ref-macro.rs:15:11
+   |
+LL |         x(123);
+   |           ^^^
+   |           |
+   |           expected `&mut i32`, found integer
+   |           help: consider mutably borrowing here: `&mut 123`
+...
+LL |     bla!();
+   |     ------- in this macro invocation
+   |
+   = note: this error originates in the macro `bla` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/suggest-ref-macro.rs:26:10
+   |
+LL |     bla!(456);
+   |          ^^^
+   |          |
+   |          expected `&mut i32`, found integer
+   |          help: consider mutably borrowing here: `&mut 456`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.