Rollup merge of #135572 - jieyouxu:migrate-split-debuginfo, r=davidtwco

tests: Port `split-debuginfo` to rmake.rs

Part of #121876.

This PR supersedes #128754 and is co-authored with `@Oneirical.`

## Known limitations

- In general, like the `Makefile` version, this test in its present form is also somewhat funny because for the most part it merely checks for existence/absence of output artifacts but makes no attempt to actually check if the debuginfo is at all usable.

## Changes

This PR ports `tests/run-make/split-debuginfo` to rmake.rs. This is an **initial** port, and certainly could be cleaned up and/or enhanced.

The original Makefile version had several functional problems. I fixed some of them, but also left some existing issues as-is.

1. The linux/non-linux final branch had a conditional interpolation of `UNSTABLE_OPTIONS := -Zunstable-options`. However, one of the use sites was `-C $(UNSTABLE_OPTIONS) split-debuginfo`. This indicates to me that this run-make test is not run in CI under a non-linux + non-windows + non-darwin environment, because that would've failed as this would expand to `-C -Zunstable-options split-debuginfo`. I fixed this in the rmake.rs version, but I'm not sure if this distinction is worth keeping at all if it's not tested in CI.
2. There are several comments that were discovered to be wrong. I tried to fix them in the rmake.rs version as well.
3. The check for path remapping / lack of path remapping through

    ```make
    objdump -Wi $(TMPDIR)/foo | grep DW_AT_GNU_dwo_name | (! grep $(TMPDIR)) || exit 1
    ```

    is incorrect, because that looks at the single line of that contains `DW_AT_GNU_dwo_name`. This is unfortunately wrong because empirical evidence shows that with `objdump`[^objdump], the check actually needs to look at the attribute value of `DW_AT_comp_dir` on the previous line not `DW_AT_GNU_dwo_name`[^gnu-ext]. Example output of `objdump`:

	```text
    <10>   DW_AT_comp_dir    : (indirect string, offset: 0xafb48): /home/joe/repos/rust
    <14>   DW_AT_GNU_dwo_name: (indirect string, offset: 0x5d1b0): foo.foo.fc848df41df7a00d-cgu.0.rcgu.dwo
	```

	In the rmake.rs version I used a 2-line sliding window to check for `DW_AT_comp_dir` and `DW_AT_GNU_dwo_name`, but to look at `DW_AT_comp_dir` specifically.
4. I included a bunch of FIXMEs and ENHANCEMENTs I noticed regarding the test because I didn't want to fix them in this initial port[^enhancement].
5. The Makefile version didn't test *anything* on Windows (both windows-msvc and windows-gnu). I added some *very* basic and *very* sparse checks for windows-msvc, but I am not willing to spend the effort to expand test coverage to windows-gnu in this initial port.
6. This run-make test is way too big. But I didn't want to expend the effort of breaking this up in this initial port.

[^objdump]: the output format differs between `objdump` and `llvm-objdump`, but the same is true for `llvm-objdump` that this is looking at the wrong line.
[^gnu-ext]: AFAICT that is a GNU DWARF attribute extension, since it isn't mentioned in DWARFv5 spec
[^enhancement]: For instance, the previous path remapping check could in theory be precisely inspected by inspecting `.debug_info` section to look for attribute value of `DW_AT_comp_dir`. But that involves resolving the value of the indirect string, which means you have to: (1) look for offset into string offset table and (2) use *that* offset to find the string itself in the string table. The split part of "split-debuginfo" makes this murky for me, so I wasn't able to replace `llvm-objdump` textual output substring matches with more precise `object` + `gimli` inspections.

## Review advice

- I'm sorry for how long the rmake.rs test ended up, but a lot of it is comments and just vertical space due to formatting. If there's any ways to make this test less long / convoluted, advice would be appreciated.
- This PR *intentionally* introduces several intermediate commits for the `Makefile`, mostly to illustrate the problems I discovered when looking at the original `Makefile` version. This is intended to highlight the existing problems in the `Makefile` version for the reviewer[^squash].
    - There are several intentional non-functional commits:
        1. Reindent the `Makefile` to make the platform conditional gating more obvious.
        2. Collapse nested if-else branches into an else if construct, which is not supported by GNU Make 3.80.
        3. Remove all redundant `-C debuginfo=2` when `-g` is already specified.
- This PR is best reviewed commit-by-commit.

[^squash]: I intend to squash these intermediate commits away after the reviewer concludes that the current form of the rmake.rs test is acceptable for merge. Before then, I'll keep them to help with review.

---

try-job: x86_64-msvc
try-job: i686-msvc
try-job: i686-mingw
try-job: x86_64-mingw-1
try-job: x86_64-apple-1
try-job: aarch64-apple
try-job: test-various

Author: jieyouxu

src/tools/run-make-support/src/external_deps/rustc.rs

@@ -338,6 +338,18 @@ impl Rustc {
         self
     }
 
+    /// Specify `-C debuginfo=...`.
+    pub fn debuginfo(&mut self, level: &str) -> &mut Self {
+        self.cmd.arg(format!("-Cdebuginfo={level}"));
+        self
+    }
+
+    /// Specify `-C split-debuginfo={packed,unpacked,off}`.
+    pub fn split_debuginfo(&mut self, split_kind: &str) -> &mut Self {
+        self.cmd.arg(format!("-Csplit-debuginfo={split_kind}"));
+        self
+    }
+
     /// Pass the `--verbose` flag.
     pub fn verbose(&mut self) -> &mut Self {
         self.cmd.arg("--verbose");

src/tools/run-make-support/src/fs.rs

@@ -238,9 +238,7 @@ pub fn set_permissions<P: AsRef<Path>>(path: P, perm: std::fs::Permissions) {
     ));
 }
 
-/// A function which prints all file names in the directory `dir` similarly to Unix's `ls`.
-/// Useful for debugging.
-/// Usage: `eprintln!("{:#?}", shallow_find_dir_entries(some_dir));`
+/// List directory entries immediately under the given `dir`.
 #[track_caller]
 pub fn shallow_find_dir_entries<P: AsRef<Path>>(dir: P) -> Vec<PathBuf> {
     let paths = read_dir(dir);

src/tools/run-make-support/src/lib.rs

@@ -94,8 +94,8 @@ pub use artifact_names::{
 
 /// Path-related helpers.
 pub use path_helpers::{
-    cwd, filename_contains, filename_not_in_denylist, has_extension, has_prefix, has_suffix,
-    not_contains, path, shallow_find_files, build_root, source_root,
+    build_root, cwd, filename_contains, filename_not_in_denylist, has_extension, has_prefix,
+    has_suffix, not_contains, path, shallow_find_directories, shallow_find_files, source_root,
 };
 
 /// Helpers for scoped test execution where certain properties are attempted to be maintained.

src/tools/run-make-support/src/path_helpers.rs

@@ -59,6 +59,25 @@ pub fn shallow_find_files<P: AsRef<Path>, F: Fn(&PathBuf) -> bool>(
     matching_files
 }
 
+/// Browse the directory `path` non-recursively and return all directories which respect the
+/// parameters outlined by `closure`.
+#[track_caller]
+pub fn shallow_find_directories<P: AsRef<Path>, F: Fn(&PathBuf) -> bool>(
+    path: P,
+    filter: F,
+) -> Vec<PathBuf> {
+    let mut matching_files = Vec::new();
+    for entry in rfs::read_dir(path) {
+        let entry = entry.expect("failed to read directory entry.");
+        let path = entry.path();
+
+        if path.is_dir() && filter(&path) {
+            matching_files.push(path);
+        }
+    }
+    matching_files
+}
+
 /// Returns true if the filename at `path` does not contain `expected`.
 pub fn not_contains<P: AsRef<Path>>(path: P, expected: &str) -> bool {
     !path.as_ref().file_name().is_some_and(|name| name.to_str().unwrap().contains(expected))

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -1 +0,0 @@
-run-make/split-debuginfo/Makefile