Fix diag span errors for bad_placeholder

compiler/rustc_hir_analysis/src/collect.rs

@@ -186,8 +186,15 @@ pub(crate) fn placeholder_type_error_diag<'tcx>(
 
     let params = generics.map(|g| g.params).unwrap_or_default();
     let type_name = params.next_type_param_name(None);
+
+    let placeholder_spans = placeholder_types
+        .clone()
+        .into_iter()
+        .filter(|sp| !placeholder_types.iter().any(|sp2| sp2.source_equal(*sp) && sp2 != sp))
+        .collect::<Vec<_>>();
+
     let mut sugg: Vec<_> =
-        placeholder_types.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
+        placeholder_spans.iter().map(|sp| (*sp, (*type_name).to_string())).collect();
 
     if let Some(generics) = generics {
         if let Some(arg) = params.iter().find(|arg| {

tests/ui/errors/issue-116502-span-error.rs

@@ -0,0 +1,42 @@
+#![allow(dead_code)]
+#![allow(unused_variables)]
+macro_rules! Tuple {
+    { $A:ty,$B:ty } => { ($A, $B) }
+}
+
+fn main() {
+    let x: Tuple!(i32, i32) = (1, 2);
+}
+
+fn issue_36540() {
+    let _ = 0;
+    macro_rules! m {
+        () => {
+            _
+            //~^ ERROR in expressions
+            //~| ERROR in expressions
+            //~| ERROR the placeholder `_` is not allowed
+            //~| ERROR the placeholder `_` is not allowed
+            //~| ERROR the placeholder `_` is not allowed
+            //~| ERROR the placeholder `_` is not allowed
+        };
+    }
+    struct S<T = m!()>(m!(), T)
+    where
+        T: Trait<m!()>;
+
+    let x: m!() = m!();
+    std::cell::Cell::<m!()>::new(m!());
+    impl<T> std::ops::Index<m!()> for dyn Trait<(m!(), T)>
+    where
+        T: Trait<m!()>,
+    {
+        type Output = m!();
+        fn index(&self, i: m!()) -> &m!() {
+            unimplemented!()
+        }
+    }
+}
+
+trait Trait<T> {}
+impl Trait<i32> for i32 {}

tests/ui/errors/issue-116502-span-error.stderr

@@ -0,0 +1,106 @@
+error: in expressions, `_` can only be used on the left-hand side of an assignment
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^ `_` not allowed here
+...
+LL |     let x: m!() = m!();
+   |                   ---- in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: in expressions, `_` can only be used on the left-hand side of an assignment
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^ `_` not allowed here
+...
+LL |     std::cell::Cell::<m!()>::new(m!());
+   |                                  ---- in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for structs
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^
+   |             |
+   |             not allowed in type signatures
+   |             not allowed in type signatures
+   |             not allowed in type signatures
+...
+LL |     struct S<T = m!()>(m!(), T)
+   |             ---------- ---- in this macro invocation
+   |             |    |
+   |             |    in this macro invocation
+   |             help: use type parameters instead: `<U>`
+LL |     where
+LL |         T: Trait<m!()>;
+   |                  ---- in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for implementations
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^
+   |             |
+   |             not allowed in type signatures
+   |             not allowed in type signatures
+   |             not allowed in type signatures
+...
+LL |     impl<T> std::ops::Index<m!()> for dyn Trait<(m!(), T)>
+   |           -                 ----                 ---- in this macro invocation
+   |           |                 |
+   |           |                 in this macro invocation
+   |           help: use type parameters instead: `, U`
+LL |     where
+LL |         T: Trait<m!()>,
+   |                  ---- in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for associated types
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^ not allowed in type signatures
+...
+LL |         type Output = m!();
+   |                       ---- in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
+  --> $DIR/issue-116502-span-error.rs:15:13
+   |
+LL |             _
+   |             ^
+   |             |
+   |             not allowed in type signatures
+   |             not allowed in type signatures
+...
+LL |         fn index(&self, i: m!()) -> &m!() {
+   |                            ----      ---- in this macro invocation
+   |                            |
+   |                            in this macro invocation
+   |
+   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: use type parameters instead
+   |
+LL ~             T
+LL |
+ ...
+LL |         type Output = m!();
+LL ~         fn index<T>(&self, i: m!()) -> &m!() {
+   |
+help: try replacing `_` with the type in the corresponding trait method signature
+   |
+LL |             {type error}
+   |
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0121`.