Enable no_legacy_features on the Linux and QNX toolchains

.github/workflows/x86_64-linux.yml

@@ -42,3 +42,6 @@ jobs:
       - name: Bazel Test
         run: |
           bazel test --config=x86_64-linux -- //:language_and_standards_tests //:feature_verification_tests
+      - name: Bazel Test (force_pic)
+        run: |
+          bazel test --config=x86_64-linux --force_pic -- //feature_verification/opt_in_features:force_pic_flags_test

README.md

@@ -32,8 +32,7 @@ validates the setup, and how QNX-specific authentication and licensing fit in.
 - [Repository layout](docs/repository_layout.md)
 - [Extension API](docs/extension_api.md)
 - [Generation flow](docs/generation_flow.md)
-- [Linux toolchain feature set](docs/linux_toolchain_feature_set.md)
-- [QNX toolchain feature set](docs/qnx_toolchain_feature_set.md)
+- [Toolchain features](docs/features.md)
 - [Tests and validation](docs/tests_and_validation.md)
 - [QNX integration](docs/qnx_integration.md)
 - [Test Suite](docs/test_suite.md)

docs/features.md

@@ -0,0 +1,113 @@
+# Toolchain Features
+
+These are the `cc_toolchain` features defined by the toolchain configs in
+[`templates/linux/cc_toolchain_config.bzl.template`](../templates/linux/cc_toolchain_config.bzl.template)
+and
+[`templates/qnx/cc_toolchain_config.bzl.template`](../templates/qnx/cc_toolchain_config.bzl.template).
+
+Both toolchains enable **`no_legacy_features`**, which turns off the features
+Bazel would otherwise add implicitly. As a result every flag the toolchain emits
+comes from a feature defined explicitly below.
+
+Each entry is tagged with the platform(s) it applies to: **(both)**, **(Linux)**,
+or **(QNX)**. Unless noted as *opt-in (disabled by default)*, a feature is
+enabled by default.
+
+> **Note:** The order of features in the `features` list is significant — flags
+> from a later feature appear after those from an earlier feature on the command
+> line.
+
+## Capability markers
+- **`no_legacy_features`** (both) — Disables Bazel's implicit legacy features.
+- **`supports_pic`** (both) — Declares position-independent-code support.
+- **`supports_dynamic_linker`** (both) — Declares dynamic-linking support.
+- **`supports_fission`** (Linux) — Declares Fission (split DWARF) support.
+- **`supports_header_path_normalization`** (Linux) — Suppresses absolute-path
+  warnings for system headers.
+- **`dbg`** / **`opt`** (both) — Well-known build-mode markers used to select flags.
+
+## Compilation
+- **`unfiltered_compile_flags`** (both) — Redacts `__DATE__`/`__TIME__`/`__TIMESTAMP__`
+  for reproducible builds.
+- **`default_compile_flags`** (both) — Core compile flags plus `dbg`/`opt`
+  build-mode variants (exact flags differ per target).
+- **`pic`** (Linux) — Emits `-fPIC` when the `pic` build variable is available.
+  (On QNX `-fPIC` is part of the default compile flags.)
+- **`random_seed`** (both) — Emits `-frandom-seed=<output_file>` for
+  deterministic output.
+- **`include_paths`** (both) — Emits `-iquote` / `-I` / `-isystem` from the
+  `quote_include_paths`, `include_paths`, and `system_include_paths` variables.
+- **`preprocessor_defines`** (both) — Emits `-D` defines (from `defines` /
+  `local_defines`).
+- **`includes`** (Linux) — Emits `-include <hdr>` for force-included headers.
+- **`user_compile_flags`** (both) — Passes through user-supplied compile flags
+  (`copts`).
+- **`compiler_input_flags`** (both) — `-c` and the source file.
+- **`compiler_output_flags`** (both) — `-S` / `-E` / `-o` output flags.
+- **`compiler_library_search_paths`** (Linux) — Sets `LD_LIBRARY_PATH` so the
+  compiler binary finds its shared libraries.
+- **`dependency_file`** (both) — Generates `.d` dependency files. On QNX,
+  **`dependency_file_named_implicitly`** toggles between explicit and implicit
+  naming.
+- **`per_object_debug_info`** (Linux) — Emits `-gsplit-dwarf -g` under
+  `--fission` (guarded; no-op otherwise).
+
+## Linking / archiving
+- **`archiver_flags`** (both) — `ar` flags (`rcsD`) and the object-file list for
+  static archives.
+- **`user_link_flags`** (both) — Passes
+  through user-supplied link flags (`linkopts`).
+- **`linker_param_file`** (both) — Uses `@param_file` for linker/archiver args.
+- **`default_link_flags`** (both) — Default/hardening link flags (exact flags
+  differ per target and build mode).
+- **`library_search_directories`** (both) — Emits `-L` search paths.
+- **`runtime_library_search_directories`** (both) — Emits `-Wl,-rpath` entries
+  (`$ORIGIN` for `cc_test`, `$EXEC_ORIGIN` otherwise).
+- **`shared_flag`** (both) — `-shared` for dynamic libraries.
+- **`output_execpath_flags`** (both) — `-o` for the link output.
+- **`libraries_to_link`** (both) — Handles whole-archive, static, object-file,
+  dynamic, and versioned-dynamic library linking.
+- **`sysroot_link_flags`** (Linux) — Adds `--sysroot` / `-Wl,--sysroot` at link.
+
+### Opt-in link features (Linux)
+These mirror Bazel's legacy features and are guarded, so they are no-ops until
+the relevant build mode is active. All are enabled by default except where noted.
+- **`fission_support`** — `-Wl,--gdb-index` under `--fission`.
+- **`linkstamps`** — Passes `%{linkstamp_paths}` to the linker (`--stamp`).
+- **`force_pic_flags`** — `-pie` for executables under `--force_pic`.
+- **`strip_debug_symbols`** — `-Wl,-S` when the link output is stripped
+  (e.g. `fastbuild`/`opt`, not `dbg`).
+- **`static_libgcc`** — `-static-libgcc` when `static_link_cpp_runtimes` is on.
+- **`fully_static_link`** — `-static` for fully static executables. **Opt-in
+  (disabled by default)**, since it forces static linking for every target and
+  requires static system archives (unavailable on some toolchains, e.g. AutoSD).
+
+## Warnings (all opt-in / disabled by default)
+- **`minimal_warnings`** (both) — Baseline warning set.
+- **`strict_warnings`** (both) — Stricter warnings; implies `minimal_warnings`.
+- **`all_wall_warnings`** (Linux) — Broadest warning set; implies `strict_warnings`.
+- **`warnings_as_errors`** (both) — Adds `-Werror`.
+
+## Sanitizers (Linux, opt-in)
+- **`sanitizer`** — Base sanitizer feature.
+- **`asan`** / **`lsan`** / **`tsan`** / **`ubsan`** — Address / Leak / Thread /
+  Undefined-Behavior sanitizers; each implies `sanitizer`.
+
+## Threading
+- **`use_pthread`** (Linux) — Links with `-pthread`.
+
+## Extra flag hooks (template-substituted)
+- **`extra_compile_flags`** (both) — Extra flags for all compile actions.
+- **`extra_c_compile_flags`** / **`extra_cxx_compile_flags`** (Linux) — Extra C /
+  C++ compile flags.
+- **`extra_link_flags`** (both) — Extra link flags.
+
+## Coverage
+- **`coverage`** (both) — Base coverage feature.
+- **`gcc_coverage_map_format`** (both) — `-fprofile-arcs -ftest-coverage` at
+  compile and `-lgcov` / `--coverage` at link.
+
+## QNX environment
+- **`sdp_env`** (QNX) — Injects QNX SDP environment variables (`QNX_HOST`,
+  `QNX_TARGET`, license path, ...) into compile/link actions.
+- **`qnx_license_env_info`** (QNX) — Adds an optional license environment entry.

docs/maintenance.md

@@ -37,6 +37,42 @@ centralizes special sysroot flags in one place.
 Use explicit `gcc.sdp(...)` declarations when package metadata is local,
 experimental, or intentionally not part of the default support matrix.
 
+## Toolchain Feature Wiring
+
+Both the Linux and QNX toolchain configs enable **`no_legacy_features`**, so
+Bazel injects nothing implicitly — every compile/link/archive flag must come
+from a feature (or wiring) declared in the template. See
+[docs/features.md](features.md) for the full feature list. Not everything is a
+feature, though; some behavior is provided by other toolchain wiring:
+
+- **Compiler / archiver / strip tools** are bound through `action_config`
+  entries (`assemble`, `c_compile`, `cpp_compile`, the link actions, and
+  `cpp_link_static_library`), not `tool_paths`. The static-library action
+  `implies = ["archiver_flags"]`, so the `archiver_flags` feature only supplies
+  the flags while the `action_config` supplies the `ar` binary.
+- **`gcov`** is provided via `tool_paths` (`gcov_wrapper`).
+- **Sysroot (Linux)** — the sysroot path is passed as `builtin_sysroot` to
+  `create_cc_toolchain_config_info`; compile-time header resolution relies on
+  `cxx_builtin_include_directories`, so no `--sysroot` is needed at compile.
+  Link-time `--sysroot` / `-Wl,--sysroot` is emitted by the custom
+  `sysroot_link_flags` feature. There is intentionally no legacy `sysroot`
+  compile feature.
+- **Sysroot / system includes (QNX)** — QNX does not use `builtin_sysroot`;
+  system include roots come from `cxx_builtin_include_directories` (SDP paths),
+  and the SDP environment is injected by the `sdp_env` feature.
+
+When adding or auditing a feature, classify how each required behavior is
+provided: an **explicit feature** in the `features` list, **tool/sysroot wiring**
+as above, or **flags baked into another feature** (e.g. `-fPIC` is an explicit
+`pic` feature on Linux but part of `default_compile_flags` on QNX). Under
+`no_legacy_features` nothing is supplied automatically, so a missing behavior
+means a broken build rather than a silent fallback.
+
+> **Static archives:** `fully_static_link` (`-static`) requires static system
+> libraries (`libc.a`, `libstdc++.a`, ...). Toolchains that ship only shared
+> libraries (e.g. AutoSD) cannot link fully static binaries, so that feature is
+> opt-in and its test is marked incompatible with such platforms.
+
 ## Common Gotchas
 
 - runtime-specific toolchains may need extra include and link flags that do not