Move the extra directives for Mode::CoverageRun into iter_header

When these extra directives were ported over as part of #112300, it made sense
to introduce `iter_header_extra` and pass them in as an extra argument.

But now that #120881 has added a `mode` parameter to `iter_header` for its own
purposes, it's slightly simpler to move the coverage special-case code directly
into `iter_header` as well. This lets us get rid of `iter_header_extra`.

src/tools/compiletest/src/header.rs

@@ -671,17 +671,6 @@ pub fn line_directive<'line>(
     }
 }
 
-fn iter_header<R: Read>(
-    mode: Mode,
-    suite: &str,
-    poisoned: &mut bool,
-    testfile: &Path,
-    rdr: R,
-    it: &mut dyn FnMut(HeaderLine<'_>),
-) {
-    iter_header_extra(mode, suite, poisoned, testfile, rdr, &[], it)
-}
-
 /// This is generated by collecting directives from ui tests and then extracting their directive
 /// names. This is **not** an exhaustive list of all possible directives. Instead, this is a
 /// best-effort approximation for diagnostics.
@@ -812,23 +801,37 @@ struct HeaderLine<'ln> {
     line_number: usize,
 }
 
-fn iter_header_extra(
+fn iter_header(
     mode: Mode,
     suite: &str,
     poisoned: &mut bool,
     testfile: &Path,
     rdr: impl Read,
-    extra_directives: &[&str],
     it: &mut dyn FnMut(HeaderLine<'_>),
 ) {
     if testfile.is_dir() {
         return;
     }
 
-    // Process any extra directives supplied by the caller (e.g. because they
-    // are implied by the test mode), with a dummy line number of 0.
-    for directive in extra_directives {
-        it(HeaderLine { header_revision: None, original_line: "", directive, line_number: 0 });
+    // Coverage tests in coverage-run mode always have these extra directives,
+    // without needing to specify them manually in every test file.
+    // (Some of the comments below have been copied over from the old
+    // `tests/run-make/coverage-reports/Makefile`, which no longer exists.)
+    if mode == Mode::CoverageRun {
+        let extra_directives: &[&str] = &[
+            "needs-profiler-support",
+            // FIXME(mati865): MinGW GCC miscompiles compiler-rt profiling library but with Clang it works
+            // properly. Since we only have GCC on the CI ignore the test for now.
+            "ignore-windows-gnu",
+            // FIXME(pietroalbini): this test currently does not work on cross-compiled
+            // targets because remote-test is not capable of sending back the *.profraw
+            // files generated by the LLVM instrumentation.
+            "ignore-cross-compile",
+        ];
+        // Process the extra implied directives, with a dummy line number of 0.
+        for directive in extra_directives {
+            it(HeaderLine { header_revision: None, original_line: "", directive, line_number: 0 });
+        }
     }
 
     let comment = if testfile.extension().is_some_and(|e| e == "rs") {
@@ -1160,35 +1163,14 @@ pub fn make_test_description<R: Read>(
     let mut ignore_message = None;
     let mut should_fail = false;
 
-    let extra_directives: &[&str] = match config.mode {
-        // The coverage-run tests are treated as having these extra directives,
-        // without needing to specify them manually in every test file.
-        // (Some of the comments below have been copied over from
-        // `tests/run-make/coverage-reports/Makefile`, which no longer exists.)
-        Mode::CoverageRun => {
-            &[
-                "needs-profiler-support",
-                // FIXME(mati865): MinGW GCC miscompiles compiler-rt profiling library but with Clang it works
-                // properly. Since we only have GCC on the CI ignore the test for now.
-                "ignore-windows-gnu",
-                // FIXME(pietroalbini): this test currently does not work on cross-compiled
-                // targets because remote-test is not capable of sending back the *.profraw
-                // files generated by the LLVM instrumentation.
-                "ignore-cross-compile",
-            ]
-        }
-        _ => &[],
-    };
-
     let mut local_poisoned = false;
 
-    iter_header_extra(
+    iter_header(
         config.mode,
         &config.suite,
         &mut local_poisoned,
         path,
         src,
-        extra_directives,
         &mut |HeaderLine { header_revision, original_line, directive: ln, line_number }| {
             if header_revision.is_some() && header_revision != cfg {
                 return;