rustc: add support for split debuginfo (aka fission)

rust/private/rustc.bzl

@@ -1240,6 +1240,13 @@ def rustc_compile_action(
     if experimental_use_cc_common_link:
         emit = ["obj"]
 
+    use_split_debuginfo = cc_common.is_enabled(feature_configuration = feature_configuration, feature_name = "per_object_debug_info") and ctx.fragments.cpp.fission_active_for_current_compilation_mode()
+    if use_split_debuginfo:
+        rust_flags = rust_flags + [
+            "--codegen=split-debuginfo=unpacked",
+            "--codegen=debuginfo=full",
+        ]
+
     args, env_from_args = construct_arguments(
         ctx = ctx,
         attr = attr,
@@ -1340,6 +1347,13 @@ def rustc_compile_action(
         elif toolchain.target_os == "darwin":
             dsym_folder = ctx.actions.declare_directory(crate_info.output.basename + ".dSYM", sibling = crate_info.output)
             action_outputs.append(dsym_folder)
+    if use_split_debuginfo:
+        fission_directory = crate_info.name + "_fission"
+        if output_hash:
+            fission_directory = fission_directory + output_hash
+        dwo_outputs = ctx.actions.declare_directory(fission_directory, sibling = crate_info.output)
+        args.process_wrapper_flags.add("--kludge-move-dwo-to", dwo_outputs.path)
+        action_outputs.append(dwo_outputs)
 
     if ctx.executable._process_wrapper:
         # Run as normal
@@ -1398,15 +1412,19 @@ def rustc_compile_action(
     else:
         fail("No process wrapper was defined for {}".format(ctx.label))
 
+    cco_args = {}
     if experimental_use_cc_common_link:
         # Wrap the main `.o` file into a compilation output suitable for
         # cc_common.link. The main `.o` file is useful in both PIC and non-PIC
         # modes.
-        compilation_outputs = cc_common.create_compilation_outputs(
-            objects = depset([output_o]),
-            pic_objects = depset([output_o]),
-        )
-
+        cco_args["objects"] = depset([output_o])
+        cco_args["pic_objects"] = depset([output_o])
+    if use_split_debuginfo:
+        cco_args["dwo_objects"] = depset([dwo_outputs])  # buildifier: disable=uninitialized
+        cco_args["pic_dwo_objects"] = depset([dwo_outputs])  # buildifier: disable=uninitialized
+    compilation_outputs = cc_common.create_compilation_outputs(**cco_args)
+    debug_context = cc_common.create_debug_context(compilation_outputs)
+    if experimental_use_cc_common_link:
         malloc_library = ctx.attr._custom_malloc or ctx.attr.malloc
 
         # Collect the linking contexts of the standard library and dependencies.
@@ -1551,7 +1569,7 @@ def rustc_compile_action(
     else:
         providers.extend([crate_info, dep_info])
 
-    providers += establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_configuration, interface_library)
+    providers += establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_configuration, interface_library, debug_context)
 
     output_group_info = {}
 
@@ -1638,7 +1656,7 @@ def _add_codegen_units_flags(toolchain, args):
 
     args.add("-Ccodegen-units={}".format(toolchain._codegen_units))
 
-def establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_configuration, interface_library):
+def establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_configuration, interface_library, debug_context = None):
     """If the produced crate is suitable yield a CcInfo to allow for interop with cc rules
 
     Args:
@@ -1649,7 +1667,7 @@ def establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_co
         cc_toolchain (CcToolchainInfo): The current `CcToolchainInfo`
         feature_configuration (FeatureConfiguration): Feature configuration to be queried.
         interface_library (File): Optional interface library for cdylib crates on Windows.
-
+        debug_context (DebugContext): Optional debug context.
     Returns:
         list: A list containing the CcInfo provider
     """
@@ -1715,7 +1733,10 @@ def establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_co
     )
 
     cc_infos = [
-        CcInfo(linking_context = linking_context),
+        CcInfo(
+            linking_context = linking_context,
+            debug_context = debug_context,
+        ),
         toolchain.stdlib_linkflags,
     ]
 

util/process_wrapper/main.rs

@@ -184,6 +184,24 @@ fn main() -> Result<(), ProcessWrapperError> {
                 ))
             })?;
         }
+        if let Some(dwp_destination) = opts.kludge_move_dwo_to {
+            // find all .dwo files in our out_dir (how do we get that? --out-dir?)
+            // move them all to dwp_destination
+            let dest = std::path::Path::new(&dwp_destination);
+            // Unwrap is okay because we know that --kludge-move-dwo-two will be a child of
+            // rustc's --out-dir.
+            let out_dir = dest.parent().unwrap();
+            let paths = std::fs::read_dir(out_dir).unwrap();
+            for p in paths {
+                let p = p.unwrap();
+                let fn_ = p.file_name();
+                let basename = fn_.to_string_lossy();
+                if basename.ends_with(".dwo") {
+                    let tgt = dest.join(fn_);
+                    std::fs::rename(p.path(), tgt).map_err(|e| ProcessWrapperError(format!("failed to rename dwo output: {}", e)))?;
+                }
+            }
+        }
     }
 
     exit(code)

util/process_wrapper/options.rs

@@ -49,6 +49,8 @@ pub(crate) struct Options {
     pub(crate) rustc_quit_on_rmeta: bool,
     // This controls the output format of rustc messages.
     pub(crate) rustc_output_format: Option<rustc::ErrorFormat>,
+    // If set, move any produced .dwo files into the named directory.
+    pub(crate) kludge_move_dwo_to: Option<String>,
 }
 
 pub(crate) fn options() -> Result<Options, OptionError> {
@@ -67,6 +69,7 @@ pub(crate) fn options() -> Result<Options, OptionError> {
     let mut rustc_quit_on_rmeta_raw = None;
     let mut rustc_output_format_raw = None;
     let mut flags = Flags::new();
+    let mut kludge_move_dwo_to = None;
     flags.define_repeated_flag("--subst", "", &mut subst_mapping_raw);
     flags.define_flag("--stable-status-file", "", &mut stable_status_file_raw);
     flags.define_flag("--volatile-status-file", "", &mut volatile_status_file_raw);
@@ -114,6 +117,11 @@ pub(crate) fn options() -> Result<Options, OptionError> {
         Default: `rendered`",
         &mut rustc_output_format_raw,
     );
+    flags.define_flag(
+        "--kludge-move-dwo-to",
+        "If set, move all produced .dwo files to the specified directory.",
+        &mut kludge_move_dwo_to,
+    );
 
     let mut child_args = match flags
         .parse(env::args().collect())
@@ -212,6 +220,7 @@ pub(crate) fn options() -> Result<Options, OptionError> {
         output_file,
         rustc_quit_on_rmeta,
         rustc_output_format,
+        kludge_move_dwo_to,
     })
 }