Auto merge of rust-lang#146376 - durin42:dwo-specify-path, r=davidtwco

debuginfo: add an unstable flag to write split DWARF to an explicit directory

Bazel requires knowledge of outputs from actions at analysis time, including file or directory name. In order to work around the lack of predictable output name for dwo files, we group the dwo files in a subdirectory of --out-dir as a post-processing step before returning control to bazel. Unfortunately some debugging workflows rely on directly opening the dwo file rather than loading the merged dwp file, and our trick of moving the files breaks those users. We can't just hardlink the file or copy it, because with remote build execution we wouldn't end up with the un-moved file copied back to the developer's workstation. As a fix, we add this unstable flag that causes dwo files to be written to a build-system-controllable location, which then lets bazel hoover up the dwo files, but the objects also have the correct path for the dwo files.

r? `@davidtwco`

Author: bors

compiler/rustc_interface/src/util.rs

@@ -542,6 +542,7 @@ pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> Outpu
                 stem,
                 None,
                 sess.io.temps_dir.clone(),
+                sess.opts.unstable_opts.split_dwarf_out_dir.clone(),
                 sess.opts.cg.extra_filename.clone(),
                 sess.opts.output_types.clone(),
             )
@@ -571,6 +572,7 @@ pub fn build_output_filenames(attrs: &[ast::Attribute], sess: &Session) -> Outpu
                 out_filestem,
                 ofile,
                 sess.io.temps_dir.clone(),
+                sess.opts.unstable_opts.split_dwarf_out_dir.clone(),
                 sess.opts.cg.extra_filename.clone(),
                 sess.opts.output_types.clone(),
             )

compiler/rustc_session/src/config.rs

@@ -1195,6 +1195,7 @@ pub struct OutputFilenames {
     filestem: String,
     pub single_output_file: Option<OutFileName>,
     temps_directory: Option<PathBuf>,
+    explicit_dwo_out_directory: Option<PathBuf>,
     pub outputs: OutputTypes,
 }
 
@@ -1227,13 +1228,15 @@ impl OutputFilenames {
         out_filestem: String,
         single_output_file: Option<OutFileName>,
         temps_directory: Option<PathBuf>,
+        explicit_dwo_out_directory: Option<PathBuf>,
         extra: String,
         outputs: OutputTypes,
     ) -> Self {
         OutputFilenames {
             out_directory,
             single_output_file,
             temps_directory,
+            explicit_dwo_out_directory,
             outputs,
             crate_stem: format!("{out_crate_name}{extra}"),
             filestem: format!("{out_filestem}{extra}"),
@@ -1283,7 +1286,14 @@ impl OutputFilenames {
         codegen_unit_name: &str,
         invocation_temp: Option<&str>,
     ) -> PathBuf {
-        self.temp_path_ext_for_cgu(DWARF_OBJECT_EXT, codegen_unit_name, invocation_temp)
+        let p = self.temp_path_ext_for_cgu(DWARF_OBJECT_EXT, codegen_unit_name, invocation_temp);
+        if let Some(dwo_out) = &self.explicit_dwo_out_directory {
+            let mut o = dwo_out.clone();
+            o.push(p.file_name().unwrap());
+            o
+        } else {
+            p
+        }
     }
 
     /// Like `temp_path`, but also supports things where there is no corresponding

compiler/rustc_session/src/options.rs

@@ -2634,6 +2634,8 @@ written to standard error output)"),
                  file which is ignored by the linker
         `single`: sections which do not require relocation are written into object file but ignored
                   by the linker"),
+    split_dwarf_out_dir : Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
+        "location for writing split DWARF objects (`.dwo`) if enabled"),
     split_lto_unit: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "enable LTO unit splitting (default: no)"),
     src_hash_algorithm: Option<SourceFileHashAlgorithm> = (None, parse_src_file_hash, [TRACKED],

src/doc/unstable-book/src/compiler-flags/split-dwarf-out-dir.md

@@ -0,0 +1,7 @@
+# `split-dwarf-out-dir`
+
+On systems which use DWARF debug info this flag causes `.dwo` files produced
+by `-C split-debuginfo` to be written to the specified directory rather than
+placed next to the object files. This is mostly useful if you have a build
+system which needs to control where to find compile outputs without running the
+compiler and have to put your `.dwo` files in a separate directory.

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

@@ -366,6 +366,13 @@ impl Rustc {
         self
     }
 
+    pub fn split_dwarf_out_dir(&mut self, out_dir: Option<&str>) -> &mut Self {
+        if let Some(out_dir) = out_dir {
+            self.cmd.arg(format!("-Zsplit-dwarf-out-dir={out_dir}"));
+        }
+        self
+    }
+
     /// Pass the `--verbose` flag.
     pub fn verbose(&mut self) -> &mut Self {
         self.cmd.arg("--verbose");