Unrolled build for #141751

Rollup merge of #141751 - jieyouxu:remap, r=Kobzol

Remap compiler vs non-compiler sources differently (bootstrap side)

See [#t-compiler/help > Span pointing to wrong file location (`rustc-dev` component)](https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/Span.20pointing.20to.20wrong.20file.20location.20.28.60rustc-dev.60.20component.29/with/521087083).

The path remapping and unremapping for compiler sources (distributed via `rustc-dev` dist component) is broken because bootstrap currently remaps all sources unconditionally (if remapping is enabled) to the `/rustc/{hash}` form. However, the `rustc-dev` dist component (compiler sources) and `rust-src` dist component (library sources) unpacks differently:

- `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`[^note],

meaning that the compiler need to unremap them differently. But the same remapping means that the compiler has no way to distinguish between compiler and non-compiler (esp. standard library) sources. To remedy this, this PR adopts the approach of:

- remapping compiler sources (corresponding to `rustc-dev` dist component) with `/rustc-dev/{hash}` (this is `RemapScheme::Compiler`), and
- remapping non-compiler sources (corresponding to `rust-src` dist component or other non-compiler sources) with `/rustc/{hash}` (this is `RemapScheme::NonCompiler`).

A different remapping allows the compiler to reverse the remapping differently.

This PR implements the bootstrap side. A follow-up compiler-side change is needed to implement the unremapping change to address the reported issue completely.

This PR introduces another env var `CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR` that is made available to the compiler when building compiler sources to know what the remap scheme for `rustc-dev` (`RemapScheme::Compiler`) is. Compiler sources are built with the compiler remapping scheme.

As far as I know, this change should not introduce new regressions, because the compiler source unremapping (through `rustc-dev`) is already broken.

[^note]: (Notice the `src` vs `rustc-src` difference.)

Author: rust-timer

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

@@ -11,7 +11,7 @@ use crate::utils::build_stamp;
 use crate::utils::helpers::{self, LldThreads, check_cfg_arg, linker_args, linker_flags};
 use crate::{
     BootstrapCommand, CLang, Compiler, Config, DocTests, DryRun, EXTRA_CHECK_CFGS, GitRepo, Mode,
-    TargetSelection, command, prepare_behaviour_dump_dir, t,
+    RemapScheme, TargetSelection, command, prepare_behaviour_dump_dir, t,
 };
 
 /// Represents flag values in `String` form with whitespace delimiter to pass it to the compiler
@@ -920,13 +920,46 @@ impl Builder<'_> {
             hostflags.arg(format!("-Ctarget-feature={sign}crt-static"));
         }
 
-        if let Some(map_to) = self.build.debuginfo_map_to(GitRepo::Rustc) {
-            let map = format!("{}={}", self.build.src.display(), map_to);
-            cargo.env("RUSTC_DEBUGINFO_MAP", map);
+        // `rustc` needs to know the remapping scheme, in order to know how to reverse it (unremap)
+        // later. Two env vars are set and made available to the compiler
+        //
+        // - `CFG_VIRTUAL_RUST_SOURCE_BASE_DIR`: `rust-src` remap scheme (`NonCompiler`)
+        // - `CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR`: `rustc-dev` remap scheme (`Compiler`)
+        //
+        // Keep this scheme in sync with `rustc_metadata::rmeta::decoder`'s
+        // `try_to_translate_virtual_to_real`.
+        //
+        // `RUSTC_DEBUGINFO_MAP` is used to pass through to the underlying rustc
+        // `--remap-path-prefix`.
+        match mode {
+            Mode::Rustc | Mode::Codegen => {
+                if let Some(ref map_to) =
+                    self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::NonCompiler)
+                {
+                    cargo.env("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR", map_to);
+                }
 
-            // `rustc` needs to know the virtual `/rustc/$hash` we're mapping to,
-            // in order to opportunistically reverse it later.
-            cargo.env("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR", map_to);
+                if let Some(ref map_to) =
+                    self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::Compiler)
+                {
+                    // When building compiler sources, we want to apply the compiler remap scheme.
+                    cargo.env(
+                        "RUSTC_DEBUGINFO_MAP",
+                        format!("{}={}", self.build.src.display(), map_to),
+                    );
+                    cargo.env("CFG_VIRTUAL_RUSTC_DEV_SOURCE_BASE_DIR", map_to);
+                }
+            }
+            Mode::Std | Mode::ToolBootstrap | Mode::ToolRustc | Mode::ToolStd => {
+                if let Some(ref map_to) =
+                    self.build.debuginfo_map_to(GitRepo::Rustc, RemapScheme::NonCompiler)
+                {
+                    cargo.env(
+                        "RUSTC_DEBUGINFO_MAP",
+                        format!("{}={}", self.build.src.display(), map_to),
+                    );
+                }
+            }
         }
 
         if self.config.rust_remap_debuginfo {

src/bootstrap/src/lib.rs

@@ -272,6 +272,16 @@ impl Mode {
     }
 }
 
+/// When `rust.rust_remap_debuginfo` is requested, the compiler needs to know how to
+/// opportunistically unremap compiler vs non-compiler sources. We use two schemes,
+/// [`RemapScheme::Compiler`] and [`RemapScheme::NonCompiler`].
+pub enum RemapScheme {
+    /// The [`RemapScheme::Compiler`] scheme will remap to `/rustc-dev/{hash}`.
+    Compiler,
+    /// The [`RemapScheme::NonCompiler`] scheme will remap to `/rustc/{hash}`.
+    NonCompiler,
+}
+
 #[derive(Debug, Hash, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum CLang {
     C,
@@ -1217,15 +1227,32 @@ Executed at: {executed_at}"#,
         })
     }
 
-    fn debuginfo_map_to(&self, which: GitRepo) -> Option<String> {
+    fn debuginfo_map_to(&self, which: GitRepo, remap_scheme: RemapScheme) -> 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 remap_scheme {
+                    RemapScheme::Compiler => {
+                        // 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 scheme in sync with `rustc_metadata::rmeta::decoder`'s
+                        // `try_to_translate_virtual_to_real`.
+                        Some(format!("/rustc-dev/{sha}"))
+                    }
+                    RemapScheme::NonCompiler => {
+                        // For non-compiler sources, use `/rustc/{sha}` remapping scheme.
+                        Some(format!("/rustc/{sha}"))
+                    }
+                }
             }
             GitRepo::Llvm => Some(String::from("/rustc/llvm")),
         }
@@ -1292,7 +1319,7 @@ 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, RemapScheme::NonCompiler) {
             let map = format!("{}={}", self.src.display(), map_to);
             let cc = self.cc(target);
             if cc.ends_with("clang") || cc.ends_with("gcc") {