test(rustflags): Verify -Cmetadata directly, not through -Cextra-filename (#14846)

### What does this PR try to resolve?

This unblocks experimenting with having these diverge for #8716

### How should we test and review this PR?

### Additional information

Author: weihanglo

crates/cargo-test-support/src/lib.rs

@@ -623,12 +623,10 @@ pub fn cargo_exe() -> PathBuf {
 /// does not have access to the raw `ExitStatus` because `ProcessError` needs
 /// to be serializable (for the Rustc cache), and `ExitStatus` does not
 /// provide a constructor.
-struct RawOutput {
-    #[allow(dead_code)]
-    code: Option<i32>,
-    stdout: Vec<u8>,
-    #[allow(dead_code)]
-    stderr: Vec<u8>,
+pub struct RawOutput {
+    pub code: Option<i32>,
+    pub stdout: Vec<u8>,
+    pub stderr: Vec<u8>,
 }
 
 /// Run and verify a [`ProcessBuilder`]
@@ -1042,34 +1040,32 @@ impl Execs {
     }
 
     #[track_caller]
-    pub fn run(&mut self) {
+    pub fn run(&mut self) -> RawOutput {
         self.ran = true;
         let mut p = (&self.process_builder).clone().unwrap();
         if let Some(stdin) = self.expect_stdin.take() {
             p.stdin(stdin);
         }
-        if let Err(e) = self.match_process(&p) {
-            panic_error(&format!("test failed running {}", p), e);
+
+        match self.match_process(&p) {
+            Err(e) => panic_error(&format!("test failed running {}", p), e),
+            Ok(output) => output,
         }
     }
 
     /// Runs the process, checks the expected output, and returns the first
     /// JSON object on stdout.
     #[track_caller]
     pub fn run_json(&mut self) -> serde_json::Value {
-        self.ran = true;
-        let p = (&self.process_builder).clone().unwrap();
-        match self.match_process(&p) {
-            Err(e) => panic_error(&format!("test failed running {}", p), e),
-            Ok(output) => serde_json::from_slice(&output.stdout).unwrap_or_else(|e| {
-                panic!(
-                    "\nfailed to parse JSON: {}\n\
+        let output = self.run();
+        serde_json::from_slice(&output.stdout).unwrap_or_else(|e| {
+            panic!(
+                "\nfailed to parse JSON: {}\n\
                      output was:\n{}\n",
-                    e,
-                    String::from_utf8_lossy(&output.stdout)
-                );
-            }),
-        }
+                e,
+                String::from_utf8_lossy(&output.stdout)
+            );
+        })
     }
 
     #[track_caller]

tests/testsuite/build.rs

@@ -82,7 +82,7 @@ fn build_with_symlink_to_path_dependency_with_build_script_in_git() {
     // It is necessary to have a sub-repository and to add files so there is an index.
     let repo = git::init(&root.join("original"));
     git::add(&repo);
-    cargo_process("build").run()
+    cargo_process("build").run();
 }
 
 #[cargo_test]

tests/testsuite/build_script.rs

@@ -5234,7 +5234,7 @@ fn dev_dep_with_links() {
         .file("bar/build.rs", "fn main() {}")
         .file("bar/src/lib.rs", "")
         .build();
-    p.cargo("check --tests").run()
+    p.cargo("check --tests").run();
 }
 
 #[cargo_test]

tests/testsuite/config.rs

@@ -1640,7 +1640,7 @@ fn cargo_target_empty_env() {
 
 "#]])
         .with_status(101)
-        .run()
+        .run();
 }
 
 #[cargo_test]

tests/testsuite/future_incompat_report.rs

@@ -453,5 +453,5 @@ big_update v1.0.0 has the following newer versions available: 2.0.0
 with_updates v1.0.0 has the following newer versions available: 1.0.1, 1.0.2, 3.0.1
 ...
 "#]])
-        .run()
+        .run();
 }

tests/testsuite/metadata.rs

@@ -3401,7 +3401,7 @@ fn metadata_links() {
 "#]]
             .is_json(),
         )
-        .run()
+        .run();
 }
 
 #[cargo_test]

tests/testsuite/open_namespaces.rs

@@ -31,7 +31,7 @@ Caused by:
   See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#open-namespaces for more information about the status of this feature.
 
 "#]])
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -100,7 +100,7 @@ fn implicit_lib_within_namespace() {
             .is_json(),
         )
         .with_stderr_data("")
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -169,7 +169,7 @@ fn implicit_bin_within_namespace() {
             .is_json(),
         )
         .with_stderr_data("")
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -256,7 +256,7 @@ fn explicit_bin_within_namespace() {
             .is_json(),
         )
         .with_stderr_data("")
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -354,7 +354,7 @@ path+[ROOTURL]/foo#foo::bar@0.0.1
 
 "#]])
         .with_stderr_data("")
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -384,7 +384,7 @@ fn update_spec_accepts_namespaced_name() {
 [LOCKING] 0 packages to latest compatible versions
 
 "#]])
-        .run()
+        .run();
 }
 
 #[cargo_test]
@@ -414,7 +414,7 @@ fn update_spec_accepts_namespaced_pkgid() {
 [LOCKING] 0 packages to latest compatible versions
 
 "#]])
-        .run()
+        .run();
 }
 
 #[cargo_test]

tests/testsuite/package.rs

@@ -3923,7 +3923,7 @@ See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for
 [PACKAGED] 6 files, [FILE_SIZE]B ([FILE_SIZE]B compressed)
 
 "#]])
-        .run()
+        .run();
 }
 
 #[cargo_test]

tests/testsuite/pkgid.rs

@@ -403,5 +403,5 @@ fn pkgid_json_message_metadata_consistency() {
 "#]]
             .is_json(),
         )
-        .run()
+        .run();
 }

tests/testsuite/precise_pre_release.rs

@@ -39,7 +39,7 @@ if you are looking for the prerelease package it needs to be specified explicitl
 perhaps a crate was updated and forgotten to be re-vendored?
 
 "#]])
-        .run()
+        .run();
 }
 
 #[cargo_test]