fix(trim-paths): custom workspace-relative member paths remap

src/compiler/trim_paths.rs

@@ -34,6 +34,9 @@ pub(crate) const UNREMAP_SUFFIX: &str = ".trim-paths.jsonl";
 /// See <https://github.com/rust-lang/cargo/issues/17309>.
 pub(crate) const WS_REMAP_ENV: &str = "__CARGO_RUSTC_BOOTSTRAP_WS_REMAP";
 
+/// A single `<from>=<to>` remap rule.
+type RemapPair = (PathBuf, String);
+
 /// Like [`trim_paths_args`] but for rustdoc invocations.
 pub(crate) fn trim_paths_args_rustdoc(
     cmd: &mut ProcessBuilder,
@@ -103,15 +106,19 @@ pub(crate) fn trim_paths_args(
 /// **†**: path dependencies outside the workspace and other uncategorized dependencies.
 ///
 /// [RFC 3127]: https://rust-lang.github.io/rfcs/3127-trim-paths.html
-pub(crate) fn trim_paths_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> [OsString; 3] {
-    [
-        join_remap(package_remap(build_runner, unit)),
-        join_remap(build_dir_remap(build_runner)),
-        join_remap(sysroot_remap(build_runner)),
-    ]
+pub(crate) fn trim_paths_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> Vec<OsString> {
+    let package = package_remap(build_runner, unit);
+    let workspace_relative = custom_workspace_relative_remap(unit, &package);
+
+    let mut remaps = Vec::with_capacity(4);
+    remaps.push(join_remap(package));
+    remaps.extend(workspace_relative.map(join_remap));
+    remaps.push(join_remap(build_dir_remap(build_runner)));
+    remaps.push(join_remap(sysroot_remap(build_runner)));
+    remaps
 }
 
-fn join_remap((from, to): (PathBuf, String)) -> OsString {
+fn join_remap((from, to): RemapPair) -> OsString {
     let mut remap = OsString::with_capacity(from.as_os_str().len() + 1 + to.len());
     remap.push(from);
     remap.push("=");
@@ -123,7 +130,7 @@ fn join_remap((from, to): (PathBuf, String)) -> OsString {
 ///
 /// This remap logic aligns with rustc:
 /// <https://github.com/rust-lang/rust/blob/c2ef3516/src/bootstrap/src/lib.rs#L1113-L1116>
-fn sysroot_remap(build_runner: &BuildRunner<'_, '_>) -> (PathBuf, String) {
+fn sysroot_remap(build_runner: &BuildRunner<'_, '_>) -> RemapPair {
     // See also `detect_sysroot_src_path()`.
     let sysroot = build_runner
         .bcx
@@ -142,7 +149,7 @@ fn sysroot_remap(build_runner: &BuildRunner<'_, '_>) -> (PathBuf, String) {
 }
 
 /// Path prefix remap rules for dependencies.
-fn package_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> (PathBuf, String) {
+fn package_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> RemapPair {
     let pkg_root = unit.pkg.root();
     let ws_root = build_runner.bcx.ws.root();
     let source_id = unit.pkg.package_id().source_id();
@@ -175,7 +182,7 @@ fn package_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> (PathBuf, S
 }
 
 /// Path prefix remap rules for dependencies within workspaces.
-fn workspace_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> (PathBuf, String) {
+fn workspace_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> RemapPair {
     let ws_root = build_runner.bcx.ws.root();
     // rustc working directory is usually workspace root.
     // However, when `-Zroot-dir` is set, it may not be.
@@ -199,6 +206,38 @@ fn workspace_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> (PathBuf,
     (from, to)
 }
 
+/// Extra remap rule for relative workspace member paths.
+///
+/// Cargo passes member source paths relative to the working directory (see [`path_args`]),
+/// so the absolute [`workspace_remap`] rule never covers them.
+///
+/// When custom prefix for workspace remap is set via [`WS_REMAP_ENV`],
+/// an extra remap rule for relative member paths is required for correctly
+/// adding prefix to member paths.
+fn custom_workspace_relative_remap(unit: &Unit, (from, to): &RemapPair) -> Option<RemapPair> {
+    // `to` staying as `.` means WS_REMAP_ENV didn't kick in.
+    if to == "." {
+        return None;
+    }
+
+    if !unit.pkg.package_id().source_id().is_path() {
+        return None;
+    }
+
+    let rel = unit.pkg.root().strip_prefix(from).ok()?;
+    if rel.as_os_str().is_empty() {
+        return None;
+    }
+
+    let mut rel_to = to.clone();
+    for comp in rel.components() {
+        // e.g., library -> <custom-prefix>/library
+        rel_to.push('/');
+        rel_to.push_str(&comp.as_os_str().to_string_lossy());
+    }
+    Some((rel.to_path_buf(), rel_to))
+}
+
 /// Finds the checkout root and revision directory name of a git dependency.
 ///
 /// This is built under this layout: `$CARGO_HOME/git/checkouts/<repo>-<hash>[-shallow]/<rev>`.
@@ -231,7 +270,7 @@ fn git_checkout<'a>(
 ///   [`file!`] macro in-place via the `OUT_DIR` environment.
 /// * On Linux, `DW_AT_GNU_dwo_name` that contains paths to split debuginfo
 ///   files (dwp and dwo).
-fn build_dir_remap(build_runner: &BuildRunner<'_, '_>) -> (PathBuf, String) {
+fn build_dir_remap(build_runner: &BuildRunner<'_, '_>) -> RemapPair {
     let from = build_runner.bcx.ws.build_dir().into_path_unlocked();
     let to = "/cargo/build-dir".to_owned();
     (from, to)
@@ -280,7 +319,7 @@ pub(crate) fn write_unremap_file(
 ) -> CargoResult<()> {
     let mut remaps = BTreeMap::new();
 
-    let mut insert = |(from, to): (PathBuf, String)| match remaps.entry(to) {
+    let mut insert = |(from, to): RemapPair| match remaps.entry(to) {
         Entry::Vacant(entry) => {
             entry.insert(from);
         }

tests/testsuite/profile_trim_paths.rs

@@ -1640,19 +1640,27 @@ fn workspace_prefix_override_from_env() {
                 version = "0.0.1"
                 edition = "2015"
 
+                [dependencies]
+                member = { path = "member" }
+
                 [profile.dev]
                 trim-paths = "object"
            "#,
         )
         .file("src/main.rs", "fn main() {}")
+        .file("member/Cargo.toml", &basic_manifest("member", "0.0.1"))
+        .file("member/src/lib.rs", "")
         .build();
 
     p.cargo("build --verbose -Ztrim-paths")
         .env("__CARGO_RUSTC_BOOTSTRAP_WS_REMAP", "/rustc-dev/1111111")
         .masquerade_as_nightly_cargo(&["-Ztrim-paths"])
         .with_stderr_data(str![[r#"
+[LOCKING] 1 package to highest compatible version
+[COMPILING] member v0.0.1 ([ROOT]/foo/member)
+[RUNNING] `rustc [..]--remap-path-prefix=[ROOT]/foo=/rustc-dev/1111111 --remap-path-prefix=member=/rustc-dev/1111111/member --remap-path-prefix=[ROOT]/foo/target=/cargo/build-dir [..]`
 [COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc [..]--remap-path-prefix=[ROOT]/foo=/rustc-dev/1111111 [..]`
+[RUNNING] `rustc [..]--remap-path-prefix=[ROOT]/foo=/rustc-dev/1111111 --remap-path-prefix=[ROOT]/foo/target=/cargo/build-dir [..]`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])