fix(fingerprint): Don't throwaway the cache on RUSTFLAGS changes

Fixes rust-lang#8716

Author: epage

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

@@ -696,6 +696,14 @@ fn compute_metadata(
         .collect::<Vec<_>>();
     dep_c_extra_filename_hashes.sort();
     dep_c_extra_filename_hashes.hash(&mut c_extra_filename_hasher);
+    // Avoid trashing the caches on RUSTFLAGS changing via `c_extra_filename`
+    //
+    // Limited to `c_extra_filename` to help with reproducible build / PGO issues.
+    if unit.mode.is_doc() || unit.mode.is_doc_scrape() {
+        unit.rustdocflags.hash(&mut c_extra_filename_hasher);
+    } else {
+        unit.rustflags.hash(&mut c_extra_filename_hasher);
+    }
 
     let c_metadata = UnitHash(c_metadata_hasher.finish());
     let c_extra_filename = UnitHash(c_extra_filename_hasher.finish());

src/cargo/core/compiler/fingerprint/mod.rs

@@ -83,7 +83,7 @@
 //! Target flags (test/bench/for_host/edition) | ✓           |                     |                        |
 //! -C incremental=… flag                      | ✓           |                     |                        |
 //! mtime of sources                           | ✓[^3]       |                     |                        |
-//! RUSTFLAGS/RUSTDOCFLAGS                     | ✓           |                     |                        |
+//! RUSTFLAGS/RUSTDOCFLAGS                     | ✓           | ✓                   |                        | ✓
 //! [`Lto`] flags                              | ✓           | ✓                   | ✓                      | ✓
 //! config settings[^5]                        | ✓           |                     |                        |
 //! `is_std`                                   |             | ✓                   | ✓                      | ✓

tests/testsuite/config_include.rs

@@ -244,7 +244,6 @@ fn works_with_cli() {
     p.cargo("check -v -Z config-include")
         .masquerade_as_nightly_cargo(&["config-include"])
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
 [CHECKING] foo v0.0.1 ([ROOT]/foo)
 [RUNNING] `rustc [..]-W unsafe-code -W unused`
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

tests/testsuite/freshness.rs

@@ -1347,7 +1347,6 @@ fn changing_rustflags_is_cached() {
     p.cargo("build -v")
         .env("RUSTFLAGS", "-C linker=cc")
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
 [COMPILING] foo v0.0.1 ([ROOT]/foo)
 [RUNNING] `rustc [..]
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
@@ -1357,19 +1356,15 @@ fn changing_rustflags_is_cached() {
 
     p.cargo("build -v")
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc [..] src/lib.rs [..]
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])
         .run();
     p.cargo("build -v")
         .env("RUSTFLAGS", "-C linker=cc")
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc [..]
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])

tests/testsuite/freshness_checksum.rs

@@ -1519,7 +1519,6 @@ fn changing_rustflags_is_cached() {
         .masquerade_as_nightly_cargo(&["checksum-freshness"])
         .env("RUSTFLAGS", "-C linker=cc")
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
 [COMPILING] foo v0.0.1 ([ROOT]/foo)
 [RUNNING] `rustc [..]
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
@@ -1530,9 +1529,7 @@ fn changing_rustflags_is_cached() {
     p.cargo("build -Zchecksum-freshness -v")
         .masquerade_as_nightly_cargo(&["checksum-freshness"])
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc [..] src/lib.rs [..]
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])
@@ -1541,9 +1538,7 @@ fn changing_rustflags_is_cached() {
         .masquerade_as_nightly_cargo(&["checksum-freshness"])
         .env("RUSTFLAGS", "-C linker=cc")
         .with_stderr_data(str![[r#"
-[DIRTY] foo v0.0.1 ([ROOT]/foo): the rustflags changed
-[COMPILING] foo v0.0.1 ([ROOT]/foo)
-[RUNNING] `rustc [..]
+[FRESH] foo v0.0.1 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])