fix(trim-paths): sanitize absolute source paths in fingerprint

With `trim-paths`,
rustc only sees remapped source paths.
There is no reason that fingerprint still tracks original paths.

This sanitizes absolute paths in Cargo fingerprint
by applying the same remap rules with trim-paths.

Without this,
moving `CARGO_HOME` would cause rebuilds,
even the compiled artifacts are byte-identical.

One caveat is that because the "object" scope doesn't remap diagonstics,
if diagnostics were also cached,
a replay may show the "wrong" cached paths.
The "all" scope doesn't have this issue btw.

Author: weihanglo

src/compiler/fingerprint/mod.rs

@@ -79,7 +79,7 @@
 //! `__CARGO_DEFAULT_LIB_METADATA`[^4]         |             | ✓                        | ✓
 //! `__CARGO_RUSTC_BOOTSTRAP_WS_REMAP`[^2]     | ✓           |                          |
 //! `package_id`                               |             | ✓                        | ✓
-//! Target src path relative to ws             | ✓           |                          |
+//! Target src path relative to ws[^9]         | ✓           |                          |
 //! Target flags (test/bench/for_host/edition) | ✓           |                          |
 //! -C incremental=… flag                      | ✓           |                          |
 //! mtime of sources                           | ✓[^3]       |                          |
@@ -111,6 +111,9 @@
 //!
 //! [^8]: including `-Cextra-filename`
 //!
+//! [^9]: Absolute source paths, for example registry deps,
+//!       are hashed after remapping when `trim-paths` is enabled.
+//!
 //! When deciding what should go in the Metadata vs the Fingerprint, consider
 //! that some files (like dylibs) do not have a hash in their filename. Thus,
 //! if a value changes, only the fingerprint will detect the change (consider,
@@ -396,6 +399,7 @@ use std::time::SystemTime;
 use anyhow::Context as _;
 use anyhow::format_err;
 use cargo_util::paths;
+use cargo_util_schemas::manifest::TomlTrimPaths;
 use filetime::FileTime;
 use serde::de;
 use serde::ser;
@@ -1705,13 +1709,35 @@ fn calculate_normal(
     let mut declared_features = unit.pkg.summary().features().keys().collect::<Vec<_>>();
     declared_features.sort(); // to avoid useless rebuild if the user orders it's features
     // differently
+
+    let src_path = {
+        // Note that .0 is hashed here, not .1 which is the cwd. That doesn't
+        // actually affect the output artifact so there's no need to hash it.
+        let src_path = path_args(build_runner.bcx.ws, unit).0;
+
+        // Some CI has random CI path for different runs.
+        // By tracking remapped paths, we avoid rebuilds when `CARGO_HOME` moves.
+        // See rust-lang/cargo#10915
+        let should_remap = match unit.profile.trim_paths {
+            TomlTrimPaths::None => false,
+            TomlTrimPaths::Object | TomlTrimPaths::All => true,
+        };
+
+        if should_remap
+            && src_path.is_absolute()
+            && let Some(remapped) = super::trim_paths::remap_path(build_runner, unit, &src_path)
+        {
+            remapped
+        } else {
+            src_path
+        }
+    };
+
     Ok(Fingerprint {
         rustc: util::hash_u64(&build_runner.bcx.rustc().verbose_version),
         target: util::hash_u64(&unit.target),
         profile: profile_hash,
-        // Note that .0 is hashed here, not .1 which is the cwd. That doesn't
-        // actually affect the output artifact so there's no need to hash it.
-        path: util::hash_u64(path_args(build_runner.bcx.ws, unit).0),
+        path: util::hash_u64(src_path),
         features: format!("{:?}", unit.features),
         declared_features: format!("{declared_features:?}"),
         deps,

src/compiler/trim_paths.rs

@@ -105,6 +105,23 @@ pub(crate) fn trim_paths_remap(build_runner: &BuildRunner<'_, '_>, unit: &Unit)
     remap_pairs(build_runner, unit).map(join_remap).collect()
 }
 
+/// Remaps `path` the same way rustc does with [`trim_paths_remap`] rules,
+/// like the last takes precedence.
+///
+/// `None` if no rule matches.
+pub(crate) fn remap_path(
+    build_runner: &BuildRunner<'_, '_>,
+    unit: &Unit,
+    path: &Path,
+) -> Option<PathBuf> {
+    remap_pairs(build_runner, unit)
+        .filter_map(|(from, to)| {
+            let rest = path.strip_prefix(&from).ok()?;
+            Some(Path::new(&to).join(rest))
+        })
+        .last()
+}
+
 /// Like [`trim_paths_remap`] but yields `(from, to)` pairs.
 fn remap_pairs(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> impl Iterator<Item = RemapPair> {
     package_remap(build_runner, unit).into_iter().chain([

tests/testsuite/profile_trim_paths.rs

@@ -2212,16 +2212,10 @@ fn cargo_home_moved_trim_paths_object() {
         .env("CARGO_HOME", &new_cargo_home)
         .with_stderr_data(
             str![[r#"
-[DIRTY] bar v0.0.1: the path to the source changed
-[COMPILING] bar v0.0.1
-[RUNNING] `rustc --crate-name bar [..]`
-[DIRTY] baz v0.0.1 ([ROOTURL]/baz#[..]): the path to the source changed
-[COMPILING] baz v0.0.1 ([ROOTURL]/baz#[..])
-[RUNNING] `rustc --crate-name baz [..]`
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc --crate-name foo [..]`
+[FRESH] bar v0.0.1
+[FRESH] baz v0.0.1 ([ROOTURL]/baz#[..])
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
-[DIRTY] foo v0.0.1 ([ROOT]/foo): info of dependency `[..]` changed
 
 "#]]
             .unordered(),
@@ -2245,16 +2239,10 @@ fn cargo_home_moved_trim_paths_all() {
         .env("CARGO_HOME", &new_cargo_home)
         .with_stderr_data(
             str![[r#"
-[DIRTY] bar v0.0.1: the path to the source changed
-[COMPILING] bar v0.0.1
-[RUNNING] `rustc --crate-name bar [..]`
-[DIRTY] baz v0.0.1 ([ROOTURL]/baz#[..]): the path to the source changed
-[COMPILING] baz v0.0.1 ([ROOTURL]/baz#[..])
-[RUNNING] `rustc --crate-name baz [..]`
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc --crate-name foo [..]`
+[FRESH] bar v0.0.1
+[FRESH] baz v0.0.1 ([ROOTURL]/baz#[..])
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
-[DIRTY] foo v0.0.1 ([ROOT]/foo): info of dependency `[..]` changed
 
 "#]]
             .unordered(),
@@ -2305,10 +2293,9 @@ fn cargo_home_moved_trim_paths_object_with_diagnostics() {
         .env("CARGO_HOME", &new_cargo_home)
         .with_stderr_data(str![[r#"
 ...
-[DIRTY] bar v0.0.1: the path to the source changed
-...
+[FRESH] bar v0.0.1
 [WARNING] unused variable: `unused`
- --> [ROOT]/home/.cargo-moved/registry/src/-[..]/bar-0.0.1/src/lib.rs:1:18
+ --> [ROOT]/home/.cargo/registry/src/-[..]/bar-0.0.1/src/lib.rs:1:18
 ...
 "#]])
         .run();