Align Cargo and Bazel Rust debug information defaults (#47748)

## Why

Keep source locations available without full debug information in ordinary builds, and retain symbols until release packaging. macOS targets also need to avoid invoking `dsymutil` in Linux remote Rust actions where it is unavailable.

## What changed

- Set Cargo's `dev` profile to `line-tables-only` and let `ci-test` inherit it through `test`. Document environment overrides for full debug information.
- Patch `rules_rs` to use line tables for `fastbuild` and `opt`, full debug information for `dbg`, and no stripping in all three modes.
- Disable split debug information for macOS toolchains, matching Cargo's release policy.

GitOrigin-RevId: 9e92b28f9647cea7dd73084febd84726b1cee279

MODULE.bazel

@@ -189,6 +189,7 @@ single_version_override(
     patch_strip = 1,
     patches = [
         "//patches:rules_rs_build_script_deps_annotation.patch",
+        "//patches:rules_rs_rust_debug_modes.patch",
         "//patches:rules_rs_windows_msvc_linker.patch",
         "//patches:rules_rs_zlib_snapshot_urls.patch",
     ],

codex-rs/Cargo.toml

@@ -598,9 +598,9 @@ ignored = [
 ]
 
 [profile.dev]
-# Keep line tables/backtraces while avoiding expensive full variable debug info
-# across local dev builds.
-debug = "limited"
+# The test profile inherits dev. Keep source locations in ordinary builds;
+# use CARGO_PROFILE_DEV_DEBUG=full (or CARGO_PROFILE_TEST_DEBUG=full) for locals.
+debug = "line-tables-only"
 
 [profile.dev-small]
 inherits = "dev"
@@ -627,7 +627,6 @@ strip = false
 
 [profile.ci-test]
 # Reduce binary size to reduce disk pressure.
-debug = "limited"
 inherits = "test"
 opt-level = 0
 

patches/BUILD.bazel

@@ -14,6 +14,7 @@ exports_files([
     "rules_foreign_cc_make_xcompile.patch",
     "rules_foreign_cc_make_msvc_stdint.patch",
     "rules_rs_build_script_deps_annotation.patch",
+    "rules_rs_rust_debug_modes.patch",
     "rules_rs_windows_msvc_linker.patch",
     "rules_rs_zlib_snapshot_urls.patch",
     "rusty_v8_prebuilt_out_dir.patch",

patches/rules_rs_rust_debug_modes.patch

@@ -0,0 +1,42 @@
+diff --git a/rs/toolchains/declare_rustc_toolchains.bzl b/rs/toolchains/declare_rustc_toolchains.bzl
+--- a/rs/toolchains/declare_rustc_toolchains.bzl
++++ b/rs/toolchains/declare_rustc_toolchains.bzl
+@@ -45,6 +45,14 @@
+             },
+         )
+         source_stdlib_building_select[config_setting] = "@rules_rs//rs/private:empty_stdlib"
++
++    # Apple targets default to packed dSYMs and invoke dsymutil at link time.
++    # The Linux remote Rust action has no dsymutil. Match Cargo release's
++    # split-debuginfo policy so line/full info remains available before packaging.
++    darwin_debug_flags = select({
++        "@platforms//os:macos": ["-Csplit-debuginfo=off"],
++        "//conditions:default": [],
++    })
+-
++
+     for triple in execs:
+         exec_triple = _parse_triple(triple)
+@@ -152,8 +160,20 @@
+                 "//conditions:default": [],
+             }),
+             default_edition = edition,
+-            extra_exec_rustc_flags = _rustc_flags_to_select(extra_exec_rustc_flags),
+-            extra_rustc_flags = _rustc_flags_to_select(extra_rustc_flags),
++            extra_exec_rustc_flags = _rustc_flags_to_select(extra_exec_rustc_flags) + darwin_debug_flags,
++            extra_rustc_flags = _rustc_flags_to_select(extra_rustc_flags) + darwin_debug_flags,
++            # Retain source locations through linking; release packaging owns
++            # extracting and stripping symbols. Keep -c dbg for full debugging.
++            debug_info = {
++                "dbg": "full",
++                "fastbuild": "line-tables-only",
++                "opt": "line-tables-only",
++            },
++            strip_level = {
++                "dbg": "none",
++                "fastbuild": "none",
++                "opt": "none",
++            },
+             exec_triple = triple,
+             target_triple = select(target_triple_select),
+             visibility = ["//visibility:public"],