Auto merge of #132035 - matthiaskrgr:rollup-ty1e4q0, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #125205 (Fixup Windows verbatim paths when used with the `include!` macro)
 - #131049 (Validate args are correct for `UnevaluatedConst`, `ExistentialTraitRef`/`ExistentialProjection`)
 - #131549 (Add a note for `?` on a `impl Future<Output = Result<..>>` in sync function)
 - #131731 (add `TestFloatParse` to `tools.rs` for bootstrap)
 - #131732 (Add doc(plugins), doc(passes), etc. to INVALID_DOC_ATTRIBUTES)
 - #132006 (don't stage-off to previous compiler when CI rustc is available)
 - #132022 (Move `cmp_in_dominator_order` out of graph dominator computation)
 - #132033 (compiletest: Make `line_directive` return a `DirectiveLine`)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_expand/src/base.rs

@@ -1,5 +1,6 @@
 use std::default::Default;
 use std::iter;
+use std::path::Component::Prefix;
 use std::path::{Path, PathBuf};
 use std::rc::Rc;
 
@@ -1293,7 +1294,12 @@ pub fn resolve_path(sess: &Session, path: impl Into<PathBuf>, span: Span) -> PRe
         base_path.push(path);
         Ok(base_path)
     } else {
-        Ok(path)
+        // This ensures that Windows verbatim paths are fixed if mixed path separators are used,
+        // which can happen when `concat!` is used to join paths.
+        match path.components().next() {
+            Some(Prefix(prefix)) if prefix.kind().is_verbatim() => Ok(path.components().collect()),
+            _ => Ok(path),
+        }
     }
 }