compiletest: Fix --exact test filtering

This fix only changes the behavior when using `--exact` test filtering, which
was quite broken. Before this fix, the following runs 0 tests:

    $ ./x test tests/run-make/crate-loading -- --exact
    running 0 tests
    test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 431 filtered out; finished in 24.95µs

With the fix the desired test is run:

    $ ./x test tests/run-make/crate-loading -- --exact
    running 1 tests
    test [run-make] tests/run-make/crate-loading ... ok

Without `--exact` the set of tests run tests is unchanged. This still runs "too many" tests

    $ ./x test tests/run-make/crate-loading
    running 3 tests
    test [run-make] tests/run-make/crate-loading-crate-depends-on-itself ... ok
    test [run-make] tests/run-make/crate-loading-multiple-candidates ... ok
    test [run-make] tests/run-make/crate-loading ... ok

This still runs the one and only right test:

    $ ./x test tests/ui/lint/unused/unused-allocation.rs
    running 1 tests
    test [ui] tests/ui/lint/unused/unused-allocation.rs ... ok

Author: Enselic

src/tools/compiletest/src/directives.rs

@@ -1446,6 +1446,7 @@ pub(crate) fn make_test_description<R: Read>(
     cache: &DirectivesCache,
     name: String,
     path: &Utf8Path,
+    filterable_path: Utf8PathBuf,
     src: R,
     test_revision: Option<&str>,
     poisoned: &mut bool,
@@ -1520,7 +1521,7 @@ pub(crate) fn make_test_description<R: Read>(
         _ => ShouldPanic::No,
     };
 
-    CollectedTestDesc { name, ignore, ignore_message, should_panic }
+    CollectedTestDesc { name, filterable_path, ignore, ignore_message, should_panic }
 }
 
 fn ignore_cdb(config: &Config, line: &str) -> IgnoreDecision {

src/tools/compiletest/src/executor.rs

@@ -12,6 +12,8 @@ use std::num::NonZero;
 use std::sync::{Arc, Mutex, mpsc};
 use std::{env, hint, io, mem, panic, thread};
 
+use camino::Utf8PathBuf;
+
 use crate::common::{Config, TestPaths};
 use crate::output_capture::{self, ConsoleOut};
 use crate::panic_hook;
@@ -293,8 +295,12 @@ fn filter_tests(opts: &Config, tests: Vec<CollectedTest>) -> Vec<CollectedTest>
     let mut filtered = tests;
 
     let matches_filter = |test: &CollectedTest, filter_str: &str| {
-        let test_name = &test.desc.name;
-        if opts.filter_exact { test_name == filter_str } else { test_name.contains(filter_str) }
+        let filterable_path = test.desc.filterable_path.as_str();
+        if opts.filter_exact {
+            filterable_path == filter_str
+        } else {
+            filterable_path.contains(filter_str)
+        }
     };
 
     // Remove tests that don't match the test filter
@@ -339,6 +345,7 @@ pub(crate) struct CollectedTest {
 /// Information that was historically needed to create a libtest `TestDesc`.
 pub(crate) struct CollectedTestDesc {
     pub(crate) name: String,
+    pub(crate) filterable_path: Utf8PathBuf,
     pub(crate) ignore: bool,
     pub(crate) ignore_message: Option<Cow<'static, str>>,
     pub(crate) should_panic: ShouldPanic,

src/tools/compiletest/src/lib.rs

@@ -317,18 +317,30 @@ pub fn parse_config(args: Vec<String>) -> Config {
             .free
             .iter()
             .map(|f| {
+                // Here `f` is relative to `./tests/run-make`. So if you run
+                //
+                //   ./x test tests/run-make/crate-loading
+                //
+                //  then `f` is "crate-loading".
                 let path = Utf8Path::new(f);
                 let mut iter = path.iter().skip(1);
 
-                // We skip the test folder and check if the user passed `rmake.rs`.
                 if iter.next().is_some_and(|s| s == "rmake.rs") && iter.next().is_none() {
+                    // Strip the "rmake.rs" suffix. For example, if `f` is
+                    // "crate-loading/rmake.rs" then this gives us "crate-loading".
                     path.parent().unwrap().to_string()
                 } else {
                     f.to_string()
                 }
             })
             .collect::<Vec<_>>()
     } else {
+        // Note that the filters are relative to the root dir of the different test
+        // suites. For example, with:
+        //
+        //   ./x test tests/ui/lint/unused
+        //
+        // the filter is "lint/unused".
         matches.free.clone()
     };
     let compare_mode = matches.opt_str("compare-mode").map(|s| {
@@ -911,7 +923,8 @@ fn make_test(cx: &TestCollectorCx, collector: &mut TestCollector, testpaths: &Te
     collector.tests.extend(revisions.into_iter().map(|revision| {
         // Create a test name and description to hand over to the executor.
         let src_file = fs::File::open(&test_path).expect("open test file to parse ignores");
-        let test_name = make_test_name(&cx.config, testpaths, revision);
+        let (test_name, filterable_path) =
+            make_test_name_and_filterable_path(&cx.config, testpaths, revision);
         // Create a description struct for the test/revision.
         // This is where `ignore-*`/`only-*`/`needs-*` directives are handled,
         // because they historically needed to set the libtest ignored flag.
@@ -920,6 +933,7 @@ fn make_test(cx: &TestCollectorCx, collector: &mut TestCollector, testpaths: &Te
             &cx.cache,
             test_name,
             &test_path,
+            filterable_path,
             src_file,
             revision,
             &mut collector.poisoned,
@@ -1072,7 +1086,11 @@ impl Stamp {
 }
 
 /// Creates a name for this test/revision that can be handed over to the executor.
-fn make_test_name(config: &Config, testpaths: &TestPaths, revision: Option<&str>) -> String {
+fn make_test_name_and_filterable_path(
+    config: &Config,
+    testpaths: &TestPaths,
+    revision: Option<&str>,
+) -> (String, Utf8PathBuf) {
     // Print the name of the file, relative to the sources root.
     let path = testpaths.file.strip_prefix(&config.src_root).unwrap();
     let debugger = match config.debugger {
@@ -1084,14 +1102,23 @@ fn make_test_name(config: &Config, testpaths: &TestPaths, revision: Option<&str>
         None => String::new(),
     };
 
-    format!(
+    let name = format!(
         "[{}{}{}] {}{}",
         config.mode,
         debugger,
         mode_suffix,
         path,
         revision.map_or("".to_string(), |rev| format!("#{}", rev))
-    )
+    );
+
+    // `path` is the full path from the repo root like, `tests/ui/foo/bar.rs`.
+    // Filtering is applied without the `tests/ui/` part, so strip that off.
+    // First strip of "tests" to make sure we don't have some unexpected path.
+    let mut filterable_path = path.strip_prefix("tests").unwrap().to_owned();
+    // Now strip of e.g. "ui" or "run-make" component.
+    filterable_path = filterable_path.components().skip(1).collect();
+
+    (name, filterable_path)
 }
 
 /// Checks that test discovery didn't find any tests whose name stem is a prefix