docs(fingerprint): cargo-rustc extra flags do not affect the metadata (…

…#14898) ### What does this PR try to resolve? As the test updates in this PR show, RUSTFLAGS and extra-flags have the same behavior: they don't affect `-Cextra-filename` or `-Cmetadata`. I also verified this by code inspection. I'm not sure why the table says this. ### How should we test and review this PR? ### Additional information
rust-lang · Dec 5, 2024 · a4a3651 · a4a3651
2 parents 9e2c367 + ce74bce
commit a4a3651
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diff --git a/src/cargo/core/compiler/fingerprint/mod.rs b/src/cargo/core/compiler/fingerprint/mod.rs
@@ -66,7 +66,7 @@
 //! -------------------------------------------|-------------|----------
 //! rustc                                      | ✓           | ✓
 //! [`Profile`]                                | ✓           | ✓
-//! `cargo rustc` extra args                   | ✓           | ✓
+//! `cargo rustc` extra args                   | ✓           |
 //! [`CompileMode`]                            | ✓           | ✓
 //! Target Name                                | ✓           | ✓
 //! `TargetKind` (bin/lib/etc.)                | ✓           | ✓

diff --git a/tests/testsuite/rustflags.rs b/tests/testsuite/rustflags.rs
@@ -1479,48 +1479,6 @@ fn env_rustflags_misspelled_build_script() {
         .run();
 }
 
-#[cargo_test]
-fn remap_path_prefix_ignored() {
-    let get_c_metadata_re =
-        regex::Regex::new(r".* (--crate-name [^ ]+).* (-C ?metadata=[^ ]+).*").unwrap();
-    let get_c_metadata = |output: RawOutput| {
-        let stderr = String::from_utf8(output.stderr).unwrap();
-        let mut c_metadata = get_c_metadata_re
-            .captures_iter(&stderr)
-            .map(|c| {
-                let (_, [name, c_metadata]) = c.extract();
-                format!("{name} {c_metadata}")
-            })
-            .collect::<Vec<_>>();
-        assert!(
-            !c_metadata.is_empty(),
-            "`{get_c_metadata_re:?}` did not match:\n```\n{stderr}\n```"
-        );
-        c_metadata.sort();
-        c_metadata.join("\n")
-    };
-
-    let p = project().file("src/lib.rs", "").build();
-
-    let build_output = p
-        .cargo("build -v")
-        .env(
-            "RUSTFLAGS",
-            "--remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo",
-        )
-        .run();
-    let build_c_metadata = dbg!(get_c_metadata(build_output));
-
-    p.cargo("clean").run();
-
-    let rustc_output = p
-        .cargo("rustc -v -- --remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo")
-        .run();
-    let rustc_c_metadata = dbg!(get_c_metadata(rustc_output));
-
-    assert_data_eq!(rustc_c_metadata, build_c_metadata);
-}
-
 #[cargo_test]
 fn remap_path_prefix_works() {
     // Check that remap-path-prefix works.
@@ -1562,6 +1520,142 @@ fn remap_path_prefix_works() {
         .run();
 }
 
+#[cargo_test]
+fn rustflags_remap_path_prefix_ignored_for_c_metadata() {
+    let p = project().file("src/lib.rs", "").build();
+
+    let build_output = p
+        .cargo("build -v")
+        .env(
+            "RUSTFLAGS",
+            "--remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo",
+        )
+        .run();
+    let first_c_metadata = dbg!(get_c_metadata(build_output));
+
+    p.cargo("clean").run();
+
+    let build_output = p
+        .cargo("build -v")
+        .env(
+            "RUSTFLAGS",
+            "--remap-path-prefix=/def=/zoo --remap-path-prefix /earth=/zoo",
+        )
+        .run();
+    let second_c_metadata = dbg!(get_c_metadata(build_output));
+
+    assert_data_eq!(first_c_metadata, second_c_metadata);
+}
+
+#[cargo_test]
+fn rustc_remap_path_prefix_ignored_for_c_metadata() {
+    let p = project().file("src/lib.rs", "").build();
+
+    let build_output = p
+        .cargo("rustc -v -- --remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo")
+        .run();
+    let first_c_metadata = dbg!(get_c_metadata(build_output));
+
+    p.cargo("clean").run();
+
+    let build_output = p
+        .cargo("rustc -v -- --remap-path-prefix=/def=/zoo --remap-path-prefix /earth=/zoo")
+        .run();
+    let second_c_metadata = dbg!(get_c_metadata(build_output));
+
+    assert_data_eq!(first_c_metadata, second_c_metadata);
+}
+
+// `--remap-path-prefix` is meant to take two different binaries and make them the same but the
+// rlib name, including `-Cextra-filename`, can still end up in the binary so it can't change
+#[cargo_test]
+fn rustflags_remap_path_prefix_ignored_for_c_extra_filename() {
+    let p = project().file("src/lib.rs", "").build();
+
+    let build_output = p
+        .cargo("build -v")
+        .env(
+            "RUSTFLAGS",
+            "--remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo",
+        )
+        .run();
+    let first_c_extra_filename = dbg!(get_c_extra_filename(build_output));
+
+    p.cargo("clean").run();
+
+    let build_output = p
+        .cargo("build -v")
+        .env(
+            "RUSTFLAGS",
+            "--remap-path-prefix=/def=/zoo --remap-path-prefix /earth=/zoo",
+        )
+        .run();
+    let second_c_extra_filename = dbg!(get_c_extra_filename(build_output));
+
+    assert_data_eq!(first_c_extra_filename, second_c_extra_filename);
+}
+
+// `--remap-path-prefix` is meant to take two different binaries and make them the same but the
+// rlib name, including `-Cextra-filename`, can still end up in the binary so it can't change
+#[cargo_test]
+fn rustc_remap_path_prefix_ignored_for_c_extra_filename() {
+    let p = project().file("src/lib.rs", "").build();
+
+    let build_output = p
+        .cargo("rustc -v -- --remap-path-prefix=/abc=/zoo --remap-path-prefix /spaced=/zoo")
+        .run();
+    let first_c_extra_filename = dbg!(get_c_extra_filename(build_output));
+
+    p.cargo("clean").run();
+
+    let build_output = p
+        .cargo("rustc -v -- --remap-path-prefix=/def=/zoo --remap-path-prefix /earth=/zoo")
+        .run();
+    let second_c_extra_filename = dbg!(get_c_extra_filename(build_output));
+
+    assert_data_eq!(first_c_extra_filename, second_c_extra_filename);
+}
+
+fn get_c_metadata(output: RawOutput) -> String {
+    let get_c_metadata_re =
+        regex::Regex::new(r".* (--crate-name [^ ]+).* (-C ?metadata=[^ ]+).*").unwrap();
+
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    let mut c_metadata = get_c_metadata_re
+        .captures_iter(&stderr)
+        .map(|c| {
+            let (_, [name, c_metadata]) = c.extract();
+            format!("{name} {c_metadata}")
+        })
+        .collect::<Vec<_>>();
+    assert!(
+        !c_metadata.is_empty(),
+        "`{get_c_metadata_re:?}` did not match:\n```\n{stderr}\n```"
+    );
+    c_metadata.sort();
+    c_metadata.join("\n")
+}
+
+fn get_c_extra_filename(output: RawOutput) -> String {
+    let get_c_extra_filename_re =
+        regex::Regex::new(r".* (--crate-name [^ ]+).* (-C ?extra-filename=[^ ]+).*").unwrap();
+
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    let mut c_extra_filename = get_c_extra_filename_re
+        .captures_iter(&stderr)
+        .map(|c| {
+            let (_, [name, c_extra_filename]) = c.extract();
+            format!("{name} {c_extra_filename}")
+        })
+        .collect::<Vec<_>>();
+    assert!(
+        !c_extra_filename.is_empty(),
+        "`{get_c_extra_filename_re:?}` did not match:\n```\n{stderr}\n```"
+    );
+    c_extra_filename.sort();
+    c_extra_filename.join("\n")
+}
+
 #[cargo_test]
 fn host_config_rustflags_with_target() {
     // regression test for https://github.com/rust-lang/cargo/issues/10206