In --emit KIND=PATH options, only hash KIND

The PATH has no material effect on the emitted artifact, and setting
the patch via `-o` or `--out-dir` does not affect the hash.

Closes https://github.com/rust-lang/rust/issues/86044

compiler/rustc_interface/src/tests.rs

@@ -152,9 +152,9 @@ fn test_output_types_tracking_hash_different_paths() {
     v2.output_types = OutputTypes::new(&[(OutputType::Exe, Some(PathBuf::from("/some/thing")))]);
     v3.output_types = OutputTypes::new(&[(OutputType::Exe, None)]);
 
-    assert_different_hash(&v1, &v2);
-    assert_different_hash(&v1, &v3);
-    assert_different_hash(&v2, &v3);
+    assert_same_hash(&v1, &v2);
+    assert_same_hash(&v1, &v3);
+    assert_same_hash(&v2, &v3);
 }
 
 #[test]

compiler/rustc_session/src/config.rs

@@ -31,6 +31,7 @@ use std::collections::btree_map::{
 };
 use std::collections::{BTreeMap, BTreeSet};
 use std::fmt;
+use std::hash::{Hash, Hasher};
 use std::iter::{self, FromIterator};
 use std::path::{Path, PathBuf};
 use std::str::{self, FromStr};
@@ -325,10 +326,19 @@ impl Default for TrimmedDefPaths {
 
 /// Use tree-based collections to cheaply get a deterministic `Hash` implementation.
 /// *Do not* switch `BTreeMap` out for an unsorted container type! That would break
-/// dependency tracking for command-line arguments.
-#[derive(Clone, Hash, Debug)]
+/// dependency tracking for command-line arguments. Also only hash keys, since tracking
+/// should only depend on the output types, not the paths they're written to.
+#[derive(Clone, Debug)]
 pub struct OutputTypes(BTreeMap<OutputType, Option<PathBuf>>);
 
+impl Hash for OutputTypes {
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        for k in self.keys() {
+            k.hash(hasher);
+        }
+    }
+}
+
 impl_stable_hash_via_hash!(OutputTypes);
 
 impl OutputTypes {

src/test/run-make/emit-path-unhashed/Makefile

@@ -0,0 +1,26 @@
+-include ../../run-make-fulldeps/tools.mk
+
+OUT=$(TMPDIR)/emit
+
+# --emit KIND=PATH should not affect crate hash vs --emit KIND
+all: $(OUT)/a/libfoo.rlib $(OUT)/b/libfoo.rlib $(TMPDIR)/libfoo.rlib
+	$(RUSTC) -Zls $(TMPDIR)/libfoo.rlib > $(TMPDIR)/base.txt
+	$(RUSTC) -Zls $(OUT)/a/libfoo.rlib > $(TMPDIR)/a.txt
+	$(RUSTC) -Zls $(OUT)/b/libfoo.rlib > $(TMPDIR)/b.txt
+
+	diff $(TMPDIR)/base.txt $(TMPDIR)/a.txt
+	diff $(TMPDIR)/base.txt $(TMPDIR)/b.txt
+
+# Default output name
+$(TMPDIR)/libfoo.rlib: foo.rs
+	$(RUSTC) --emit link foo.rs
+
+# Output named with -o
+$(OUT)/a/libfoo.rlib: foo.rs
+	mkdir -p $(OUT)/a
+	$(RUSTC) --emit link -o $@ foo.rs
+
+# Output named with KIND=PATH
+$(OUT)/b/libfoo.rlib: foo.rs
+	mkdir -p $(OUT)/b
+	$(RUSTC) --emit link=$@ foo.rs

src/test/run-make/emit-path-unhashed/foo.rs

@@ -0,0 +1 @@
+#![crate_type = "rlib"]