Make -Zsimulate-remapped-rust-src-base reproducible on CI

src/test/ui/consts/missing_span_in_backtrace.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z simulate-remapped-rust-src-base=/rustc/xyz -Z translate-remapped-path-to-local-path=no -Z ui-testing=no
+// compile-flags: -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ui-testing=no
 // normalize-stderr-test "alloc[0-9]+" -> "ALLOC_ID"
 
 #![feature(const_swap)]

src/test/ui/consts/missing_span_in_backtrace.stderr

@@ -1,18 +1,18 @@
 error[E0080]: evaluation of constant value failed
-  --> /rustc/xyz/library/core/src/ptr/mod.rs:1135:9
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
    |
    = note: unable to copy parts of a pointer from memory at ALLOC_ID
    |
    = help: this code performed an operation that depends on the underlying bytes representing a pointer
    = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported
 note: inside `std::ptr::read::<MaybeUninit<MaybeUninit<u8>>>`
-  --> /rustc/xyz/library/core/src/ptr/mod.rs:1135:9
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
 note: inside `mem::swap_simple::<MaybeUninit<MaybeUninit<u8>>>`
-  --> /rustc/xyz/library/core/src/mem/mod.rs:773:17
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
 note: inside `ptr::swap_nonoverlapping_simple_untyped::<MaybeUninit<u8>>`
-  --> /rustc/xyz/library/core/src/ptr/mod.rs:944:9
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
 note: inside `swap_nonoverlapping::<MaybeUninit<u8>>`
-  --> /rustc/xyz/library/core/src/ptr/mod.rs:925:14
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
 note: inside `X`
   --> $DIR/missing_span_in_backtrace.rs:17:9
    |

src/test/ui/span/issue-71363.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z simulate-remapped-rust-src-base=/rustc/xyz -Z translate-remapped-path-to-local-path=no -Z ui-testing=no
+// compile-flags: -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ui-testing=no
 
 struct MyError;
 impl std::error::Error for MyError {}

src/test/ui/span/issue-71363.stderr

@@ -7,7 +7,7 @@ error[E0277]: `MyError` doesn't implement `std::fmt::Display`
   = help: the trait `std::fmt::Display` is not implemented for `MyError`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `std::error::Error`
- --> /rustc/xyz/library/core/src/error.rs:31:26
+ --> $SRC_DIR/core/src/error.rs:LL:COL
   |
   = note: required by this bound in `std::error::Error`
 
@@ -20,7 +20,7 @@ error[E0277]: `MyError` doesn't implement `Debug`
   = help: the trait `Debug` is not implemented for `MyError`
   = note: add `#[derive(Debug)]` to `MyError` or manually `impl Debug for MyError`
 note: required by a bound in `std::error::Error`
- --> /rustc/xyz/library/core/src/error.rs:31:18
+ --> $SRC_DIR/core/src/error.rs:LL:COL
   |
   = note: required by this bound in `std::error::Error`
 help: consider annotating `MyError` with `#[derive(Debug)]`

src/tools/compiletest/src/runtest.rs

@@ -3542,6 +3542,8 @@ impl<'test> TestCx<'test> {
             option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR").map(PathBuf::from),
             // Virtual `/rustc/$sha` coming from download-rustc:
             std::env::var_os("FAKE_DOWNLOAD_RUSTC_PREFIX").map(PathBuf::from),
+            // Tests using -Zsimulate-remapped-rust-src-base should use this fake path
+            Some("/rustc/FAKE_PREFIX".into()),
         ];
         for base_dir in source_bases {
             if let Some(base_dir) = base_dir {