Auto merge of #129687 - Urgau:rfc3127-sysroot-2, r=jieyouxu

Implement RFC3137 trim-paths sysroot changes - take 2

This PR is a continuation of https://github.com/rust-lang/rust/pull/118149. Nothing really changed, except for https://github.com/rust-lang/rust/pull/129408 which I was able to trigger locally.

Original description:

> Implement parts of #111540
>
> Right now, backtraces into sysroot always shows /rustc/$hash in diagnostics, e.g.
>
> ```
> thread 'main' panicked at 'hello world', map-panic.rs:2:50
> stack backtrace:
>    0: std::panicking::begin_panic
>              at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/std/src/panicking.rs:616:12
>    1: map_panic::main::{{closure}}
>              at ./map-panic.rs:2:50
>    2: core::option::Option<T>::map
>              at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/option.rs:929:29
>    3: map_panic::main
>              at ./map-panic.rs:2:30
>    4: core::ops::function::FnOnce::call_once
>              at /rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52/library/core/src/ops/function.rs:248:5
> note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
> ```
>
> [RFC 3127 said](https://rust-lang.github.io/rfcs/3127-trim-paths.html#changing-handling-of-sysroot-path-in-rustc)
>
> > We want to change this behaviour such that, when rust-src source files can be discovered, the virtual path is discarded and therefore the local path will be embedded, unless there is a --remap-path-prefix that causes this local path to be remapped in the usual way.
>
> This PR implements this behaviour. When `rust-src` is present at compile time, rustc replaces /rustc/$hash with a real path into local rust-src with best effort. To sanitise this, users must explicitly supply `--remap-path-prefix=<path to rust-src>=foo`.

cc `@cbeuw`
Fix #105907
Fix #85463

try-job: dist-x86_64-linux
try-job: x86_64-msvc
try-job: dist-x86_64-msvc
try-job: armhf-gnu

src/tools/compiletest/src/header.rs

@@ -1115,6 +1115,7 @@ fn expand_variables(mut value: String, config: &Config) -> String {
     const CWD: &str = "{{cwd}}";
     const SRC_BASE: &str = "{{src-base}}";
     const BUILD_BASE: &str = "{{build-base}}";
+    const RUST_SRC_BASE: &str = "{{rust-src-base}}";
     const SYSROOT_BASE: &str = "{{sysroot-base}}";
     const TARGET_LINKER: &str = "{{target-linker}}";
     const TARGET: &str = "{{target}}";
@@ -1144,6 +1145,13 @@ fn expand_variables(mut value: String, config: &Config) -> String {
         value = value.replace(TARGET, &config.target);
     }
 
+    if value.contains(RUST_SRC_BASE) {
+        let src_base = config.sysroot_base.join("lib/rustlib/src/rust");
+        src_base.try_exists().expect(&*format!("{} should exists", src_base.display()));
+        let src_base = src_base.read_link().unwrap_or(src_base);
+        value = value.replace(RUST_SRC_BASE, &src_base.to_string_lossy());
+    }
+
     value
 }
 

src/tools/compiletest/src/runtest.rs

@@ -2294,13 +2294,19 @@ impl<'test> TestCx<'test> {
         }
 
         let base_dir = Path::new("/rustc/FAKE_PREFIX");
-        // Paths into the libstd/libcore
+        // Fake paths into the libstd/libcore
         normalize_path(&base_dir.join("library"), "$SRC_DIR");
         // `ui-fulldeps` tests can show paths to the compiler source when testing macros from
         // `rustc_macros`
         // eg. /home/user/rust/compiler
         normalize_path(&base_dir.join("compiler"), "$COMPILER_DIR");
 
+        // Real paths into the libstd/libcore
+        let rust_src_dir = &self.config.sysroot_base.join("lib/rustlib/src/rust");
+        rust_src_dir.try_exists().expect(&*format!("{} should exists", rust_src_dir.display()));
+        let rust_src_dir = rust_src_dir.read_link().unwrap_or(rust_src_dir.to_path_buf());
+        normalize_path(&rust_src_dir.join("library"), "$SRC_DIR_REAL");
+
         // Paths into the build directory
         let test_build_dir = &self.config.build_base;
         let parent_build_dir = test_build_dir.parent().unwrap().parent().unwrap().parent().unwrap();
@@ -2310,9 +2316,6 @@ impl<'test> TestCx<'test> {
         // eg. /home/user/rust/build
         normalize_path(parent_build_dir, "$BUILD_DIR");
 
-        // Paths into lib directory.
-        normalize_path(&parent_build_dir.parent().unwrap().join("lib"), "$LIB_DIR");
-
         if json {
             // escaped newlines in json strings should be readable
             // in the stderr files. There's no point int being correct,