bootstrap: remap compiler vs non-compiler sources differently

- Map compiler sources (corresponding to `rustc-dev` dist component)
  with `/rustc-dev/{hash}`.
- Map non-compiler sources (corresponding to `rust-src` dist component
  or other non-compiler sources) with `/rustc/{hash}`.

This allows the compiler to have the possibility of opportunistically
reverse the mapping. This is because

- `rust-src` unpacks sources to a path like
  `$sysroot/lib/rustlib/src/rust`, whereas
- `rustc-dev` unpacks sources to a path like
  `$sysroot/lib/rustlib/rustc-src/rust`

(Notice the `src` vs `rustc-src` difference.)

Author: jieyouxu

src/bootstrap/src/core/builder/cargo.rs

@@ -920,12 +920,13 @@ impl Builder<'_> {
             hostflags.arg(format!("-Ctarget-feature={sign}crt-static"));
         }
 
-        if let Some(map_to) = self.build.debuginfo_map_to(GitRepo::Rustc) {
+        if let Some(map_to) = self.build.debuginfo_map_to(GitRepo::Rustc, Some(mode)) {
             let map = format!("{}={}", self.build.src.display(), map_to);
             cargo.env("RUSTC_DEBUGINFO_MAP", map);
 
-            // `rustc` needs to know the virtual `/rustc/$hash` we're mapping to,
-            // in order to opportunistically reverse it later.
+            // `rustc` needs to know the virtual `/rustc/$hash` or `/rustc-dev/$hash` (depending on
+            // non-compiler sources vs compiler sources) we're mapping to, in order to
+            // opportunistically reverse it later.
             cargo.env("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR", map_to);
         }
 

src/bootstrap/src/lib.rs

@@ -1194,15 +1194,27 @@ Executed at: {executed_at}"#,
         })
     }
 
-    fn debuginfo_map_to(&self, which: GitRepo) -> Option<String> {
+    fn debuginfo_map_to(&self, which: GitRepo, mode: Option<Mode>) -> Option<String> {
         if !self.config.rust_remap_debuginfo {
             return None;
         }
 
         match which {
             GitRepo::Rustc => {
                 let sha = self.rust_sha().unwrap_or(&self.version);
-                Some(format!("/rustc/{sha}"))
+
+                match mode {
+                    // For compiler sources, remap via `/rustc-dev/{sha}` to allow distinguishing
+                    // between compiler sources vs library sources, since `rustc-dev` dist component
+                    // places them under `$sysroot/lib/rustlib/rustc-src/rust` as opposed to
+                    // `rust-src`'s `$sysroot/lib/rustlib/src/rust`.
+                    //
+                    // Keep this in sync with `rustc_metadata::rmeta::decoder`'s
+                    // `try_to_translate_virtual_to_real`.
+                    Some(Mode::Rustc) => Some(format!("/rustc-dev/{sha}")),
+                    // For non-compiler sources, just use `/rustc/{sha}` remapping.
+                    _ => Some(format!("/rustc/{sha}")),
+                }
             }
             GitRepo::Llvm => Some(String::from("/rustc/llvm")),
         }
@@ -1269,7 +1281,7 @@ Executed at: {executed_at}"#,
             base.push("-fno-omit-frame-pointer".into());
         }
 
-        if let Some(map_to) = self.debuginfo_map_to(which) {
+        if let Some(map_to) = self.debuginfo_map_to(which, None) {
             let map = format!("{}={}", self.src.display(), map_to);
             let cc = self.cc(target);
             if cc.ends_with("clang") || cc.ends_with("gcc") {