fix: -Cmetadata includes whether extra linker/rustflags is used

While we don't hash RUSTFLAGS because it may contain absolute paths that
hurts reproducibility, we track whether a unit having RUSTFLAGS applied
so that units with and without RUSTFLAGS won't clobber with each other.

src/cargo/core/compiler/build_runner/compilation_files.rs

@@ -649,6 +649,15 @@ fn compute_metadata(
     // with user dependencies.
     unit.is_std.hash(&mut hasher);
 
+    // While we don't hash RUSTFLAGS because it may contain absolute paths that
+    // hurts reproducibility, we track whether a unit having RUSTFLAGS applied
+    // so that units with and without RUSTFLAGS won't clobber with each other.
+    // This is essentially a hack for fixing rust-lang/cargo#14253.
+    let no_target_config_applied = unit.rustflags.is_empty()
+        && unit.rustdocflags.is_empty()
+        && unit.links_overrides.is_empty();
+    no_target_config_applied.hash(&mut hasher);
+
     MetaInfo {
         meta_hash: Metadata(hasher.finish()),
         use_extra_filename: should_use_metadata(bcx, unit),

tests/testsuite/rustflags.rs

@@ -1674,29 +1674,15 @@ fn host_config_shared_build_dep() {
         .arg("-Ztarget-applies-to-host")
         .arg("--config=target-applies-to-host=false")
         .env("RUSTFLAGS", "--cfg foo")
-        .with_status(101)
         // Sometimes it compiles. Not deterministic...
         .with_stderr_data(str![[r#"
 [UPDATING] `dummy-registry` index
 [LOCKING] 2 packages to latest compatible versions
 [DOWNLOADING] crates ...
 [DOWNLOADED] cc v1.0.0 (registry `dummy-registry`)
-[WARNING] output filename collision.
-The lib target `cc` in package `cc v1.0.0` has the same output filename as the lib target `cc` in package `cc v1.0.0`.
-Colliding filename is: [ROOT]/foo/target/debug/deps/libcc-[HASH].rlib
-The targets should have unique names.
-Consider changing their names to be unique or compiling them separately.
-This may become a hard error in the future; see <https://github.com/rust-lang/cargo/issues/6313>.
-[WARNING] output filename collision.
-The lib target `cc` in package `cc v1.0.0` has the same output filename as the lib target `cc` in package `cc v1.0.0`.
-Colliding filename is: [ROOT]/foo/target/debug/deps/libcc-[HASH].rmeta
-The targets should have unique names.
-Consider changing their names to be unique or compiling them separately.
-This may become a hard error in the future; see <https://github.com/rust-lang/cargo/issues/6313>.
 [COMPILING] cc v1.0.0
-[ERROR] failed to build archive: No such file or directory
-
-[ERROR] could not compile `cc` (lib) due to 1 previous error
+[COMPILING] bootstrap v0.0.0 ([ROOT]/foo)
+[FINISHED] `dev` profile [unoptimized] target(s) in [ELAPSED]s
 
 "#]])
         .run();