Add an option to save the json output from rustc to pass to rust-analyzer

BUILD.bazel

@@ -1,5 +1,17 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-load("//rust:defs.bzl", "capture_clippy_output", "clippy_flags", "error_format", "extra_exec_rustc_flag", "extra_exec_rustc_flags", "extra_rustc_flag", "extra_rustc_flags", "is_proc_macro_dep", "is_proc_macro_dep_enabled")
+load(
+    "//rust:defs.bzl",
+    "capture_clippy_output",
+    "clippy_flags",
+    "error_format",
+    "extra_exec_rustc_flag",
+    "extra_exec_rustc_flags",
+    "extra_rustc_flag",
+    "extra_rustc_flags",
+    "is_proc_macro_dep",
+    "is_proc_macro_dep_enabled",
+    "output_diagnostics",
+)
 
 exports_files(["LICENSE"])
 
@@ -18,6 +30,13 @@ error_format(
     visibility = ["//visibility:public"],
 )
 
+# This setting may be changed from the command line to generate rustc diagnostics.
+output_diagnostics(
+    name = "output_diagnostics",
+    build_setting_default = False,
+    visibility = ["//visibility:public"],
+)
+
 # This setting may be used to pass extra options to clippy from the command line.
 # It applies across all targets.
 clippy_flags(

docs/flatten.md

@@ -1379,7 +1379,8 @@ A test rule for performing `rustfmt --check` on a set of targets
 
 <pre>
 CrateInfo(<a href="#CrateInfo-aliases">aliases</a>, <a href="#CrateInfo-compile_data">compile_data</a>, <a href="#CrateInfo-deps">deps</a>, <a href="#CrateInfo-edition">edition</a>, <a href="#CrateInfo-is_test">is_test</a>, <a href="#CrateInfo-metadata">metadata</a>, <a href="#CrateInfo-name">name</a>, <a href="#CrateInfo-output">output</a>, <a href="#CrateInfo-owner">owner</a>,
-          <a href="#CrateInfo-proc_macro_deps">proc_macro_deps</a>, <a href="#CrateInfo-root">root</a>, <a href="#CrateInfo-rustc_env">rustc_env</a>, <a href="#CrateInfo-rustc_env_files">rustc_env_files</a>, <a href="#CrateInfo-srcs">srcs</a>, <a href="#CrateInfo-type">type</a>, <a href="#CrateInfo-wrapped_crate_type">wrapped_crate_type</a>)
+          <a href="#CrateInfo-proc_macro_deps">proc_macro_deps</a>, <a href="#CrateInfo-root">root</a>, <a href="#CrateInfo-rust_lib_rustc_output">rust_lib_rustc_output</a>, <a href="#CrateInfo-rust_metadata_rustc_output">rust_metadata_rustc_output</a>, <a href="#CrateInfo-rustc_env">rustc_env</a>,
+          <a href="#CrateInfo-rustc_env_files">rustc_env_files</a>, <a href="#CrateInfo-srcs">srcs</a>, <a href="#CrateInfo-type">type</a>, <a href="#CrateInfo-wrapped_crate_type">wrapped_crate_type</a>)
 </pre>
 
 A provider containing general Crate information.
@@ -1394,12 +1395,14 @@ A provider containing general Crate information.
 | <a id="CrateInfo-deps"></a>deps |  depset[DepVariantInfo]: This crate's (rust or cc) dependencies' providers.    |
 | <a id="CrateInfo-edition"></a>edition |  str: The edition of this crate.    |
 | <a id="CrateInfo-is_test"></a>is_test |  bool: If the crate is being compiled in a test context    |
-| <a id="CrateInfo-metadata"></a>metadata |  File: The rmeta file produced for this crate. It is optional.    |
+| <a id="CrateInfo-metadata"></a>metadata |  File: The output from rustc from producing the output file. It is optional.    |
 | <a id="CrateInfo-name"></a>name |  str: The name of this crate.    |
 | <a id="CrateInfo-output"></a>output |  File: The output File that will be produced, depends on crate type.    |
 | <a id="CrateInfo-owner"></a>owner |  Label: The label of the target that produced this CrateInfo    |
 | <a id="CrateInfo-proc_macro_deps"></a>proc_macro_deps |  depset[DepVariantInfo]: This crate's rust proc_macro dependencies' providers.    |
 | <a id="CrateInfo-root"></a>root |  File: The source File entrypoint to this crate, eg. lib.rs    |
+| <a id="CrateInfo-rust_lib_rustc_output"></a>rust_lib_rustc_output |  File: The output from rustc from producing the output file. It is optional.    |
+| <a id="CrateInfo-rust_metadata_rustc_output"></a>rust_metadata_rustc_output |  File: The rmeta file produced for this crate. It is optional.    |
 | <a id="CrateInfo-rustc_env"></a>rustc_env |  Dict[String, String]: Additional <code>"key": "value"</code> environment variables to set for rustc.    |
 | <a id="CrateInfo-rustc_env_files"></a>rustc_env_files |  [File]: Files containing additional environment variables to set for rustc.    |
 | <a id="CrateInfo-srcs"></a>srcs |  depset[File]: All source Files that are part of the crate.    |

docs/providers.md

@@ -11,7 +11,8 @@
 
 <pre>
 CrateInfo(<a href="#CrateInfo-aliases">aliases</a>, <a href="#CrateInfo-compile_data">compile_data</a>, <a href="#CrateInfo-deps">deps</a>, <a href="#CrateInfo-edition">edition</a>, <a href="#CrateInfo-is_test">is_test</a>, <a href="#CrateInfo-metadata">metadata</a>, <a href="#CrateInfo-name">name</a>, <a href="#CrateInfo-output">output</a>, <a href="#CrateInfo-owner">owner</a>,
-          <a href="#CrateInfo-proc_macro_deps">proc_macro_deps</a>, <a href="#CrateInfo-root">root</a>, <a href="#CrateInfo-rustc_env">rustc_env</a>, <a href="#CrateInfo-rustc_env_files">rustc_env_files</a>, <a href="#CrateInfo-srcs">srcs</a>, <a href="#CrateInfo-type">type</a>, <a href="#CrateInfo-wrapped_crate_type">wrapped_crate_type</a>)
+          <a href="#CrateInfo-proc_macro_deps">proc_macro_deps</a>, <a href="#CrateInfo-root">root</a>, <a href="#CrateInfo-rust_lib_rustc_output">rust_lib_rustc_output</a>, <a href="#CrateInfo-rust_metadata_rustc_output">rust_metadata_rustc_output</a>, <a href="#CrateInfo-rustc_env">rustc_env</a>,
+          <a href="#CrateInfo-rustc_env_files">rustc_env_files</a>, <a href="#CrateInfo-srcs">srcs</a>, <a href="#CrateInfo-type">type</a>, <a href="#CrateInfo-wrapped_crate_type">wrapped_crate_type</a>)
 </pre>
 
 A provider containing general Crate information.
@@ -26,12 +27,14 @@ A provider containing general Crate information.
 | <a id="CrateInfo-deps"></a>deps |  depset[DepVariantInfo]: This crate's (rust or cc) dependencies' providers.    |
 | <a id="CrateInfo-edition"></a>edition |  str: The edition of this crate.    |
 | <a id="CrateInfo-is_test"></a>is_test |  bool: If the crate is being compiled in a test context    |
-| <a id="CrateInfo-metadata"></a>metadata |  File: The rmeta file produced for this crate. It is optional.    |
+| <a id="CrateInfo-metadata"></a>metadata |  File: The output from rustc from producing the output file. It is optional.    |
 | <a id="CrateInfo-name"></a>name |  str: The name of this crate.    |
 | <a id="CrateInfo-output"></a>output |  File: The output File that will be produced, depends on crate type.    |
 | <a id="CrateInfo-owner"></a>owner |  Label: The label of the target that produced this CrateInfo    |
 | <a id="CrateInfo-proc_macro_deps"></a>proc_macro_deps |  depset[DepVariantInfo]: This crate's rust proc_macro dependencies' providers.    |
 | <a id="CrateInfo-root"></a>root |  File: The source File entrypoint to this crate, eg. lib.rs    |
+| <a id="CrateInfo-rust_lib_rustc_output"></a>rust_lib_rustc_output |  File: The output from rustc from producing the output file. It is optional.    |
+| <a id="CrateInfo-rust_metadata_rustc_output"></a>rust_metadata_rustc_output |  File: The rmeta file produced for this crate. It is optional.    |
 | <a id="CrateInfo-rustc_env"></a>rustc_env |  Dict[String, String]: Additional <code>"key": "value"</code> environment variables to set for rustc.    |
 | <a id="CrateInfo-rustc_env_files"></a>rustc_env_files |  [File]: Files containing additional environment variables to set for rustc.    |
 | <a id="CrateInfo-srcs"></a>srcs |  depset[File]: All source Files that are part of the crate.    |

rust/defs.bzl

@@ -49,6 +49,7 @@ load(
     _extra_rustc_flags = "extra_rustc_flags",
     _is_proc_macro_dep = "is_proc_macro_dep",
     _is_proc_macro_dep_enabled = "is_proc_macro_dep_enabled",
+    _output_diagnostics = "output_diagnostics",
 )
 load(
     "//rust/private:rustdoc.bzl",
@@ -103,6 +104,9 @@ rust_clippy = _rust_clippy
 capture_clippy_output = _capture_clippy_output
 # See @rules_rust//rust/private:clippy.bzl for a complete description.
 
+output_diagnostics = _output_diagnostics
+# See @rules_rust//rust/private:rustc.bzl for a complete description.
+
 error_format = _error_format
 # See @rules_rust//rust/private:rustc.bzl for a complete description.
 

rust/private/common.bzl

@@ -49,6 +49,10 @@ def _create_crate_info(**kwargs):
         kwargs.update({"wrapped_crate_type": None})
     if not "metadata" in kwargs:
         kwargs.update({"metadata": None})
+    if not "rust_metadata_rustc_output" in kwargs:
+        kwargs.update({"rust_metadata_rustc_output": None})
+    if not "rust_lib_rustc_output" in kwargs:
+        kwargs.update({"rust_lib_rustc_output": None})
     if not "rustc_env_files" in kwargs:
         kwargs.update({"rustc_env_files": []})
     return CrateInfo(**kwargs)

rust/private/providers.bzl

@@ -22,12 +22,14 @@ CrateInfo = provider(
         "deps": "depset[DepVariantInfo]: This crate's (rust or cc) dependencies' providers.",
         "edition": "str: The edition of this crate.",
         "is_test": "bool: If the crate is being compiled in a test context",
-        "metadata": "File: The rmeta file produced for this crate. It is optional.",
+        "metadata": "File: The output from rustc from producing the output file. It is optional.",
         "name": "str: The name of this crate.",
         "output": "File: The output File that will be produced, depends on crate type.",
         "owner": "Label: The label of the target that produced this CrateInfo",
         "proc_macro_deps": "depset[DepVariantInfo]: This crate's rust proc_macro dependencies' providers.",
         "root": "File: The source File entrypoint to this crate, eg. lib.rs",
+        "rust_lib_rustc_output": "File: The output from rustc from producing the output file. It is optional.",
+        "rust_metadata_rustc_output": "File: The rmeta file produced for this crate. It is optional.",
         "rustc_env": "Dict[String, String]: Additional `\"key\": \"value\"` environment variables to set for rustc.",
         "rustc_env_files": "[File]: Files containing additional environment variables to set for rustc.",
         "srcs": "depset[File]: All source Files that are part of the crate.",

rust/private/rust.bzl

@@ -64,6 +64,9 @@ def _assert_correct_dep_mapping(ctx):
                 ),
             )
 
+def _rustc_output_name(name):
+    return name + ".rustc-output"
+
 def _determine_lib_name(name, crate_type, toolchain, lib_hash = None):
     """See https://github.com/bazelbuild/rules_rust/issues/405
 
@@ -275,14 +278,30 @@ def _rust_library_common(ctx, crate_type):
         toolchain,
         output_hash,
     )
+
     rust_lib = ctx.actions.declare_file(rust_lib_name)
+    rust_lib_build_output = None
+    output_diagnostics = ctx.attr._output_diagnostics
+    if ctx.attr._process_wrapper and output_diagnostics:
+        rust_lib_build_output = ctx.actions.declare_file(
+            _rustc_output_name(rust_lib_name),
+            sibling = rust_lib,
+        )
 
     rust_metadata = None
+    rust_metadata_build_output = None
     if can_build_metadata(toolchain, ctx, crate_type) and not ctx.attr.disable_pipelining:
+        rust_metadata_name = paths.replace_extension(rust_lib_name, ".rmeta")
+
         rust_metadata = ctx.actions.declare_file(
-            paths.replace_extension(rust_lib_name, ".rmeta"),
+            rust_metadata_name,
             sibling = rust_lib,
         )
+        if output_diagnostics:
+            rust_metadata_build_output = ctx.actions.declare_file(
+                _rustc_output_name(rust_metadata_name),
+                sibling = rust_metadata,
+            )
 
     deps = transform_deps(ctx.attr.deps)
     proc_macro_deps = transform_deps(ctx.attr.proc_macro_deps + get_import_macro_deps(ctx))
@@ -300,7 +319,9 @@ def _rust_library_common(ctx, crate_type):
             proc_macro_deps = depset(proc_macro_deps),
             aliases = ctx.attr.aliases,
             output = rust_lib,
+            rust_lib_rustc_output = rust_lib_build_output,
             metadata = rust_metadata,
+            rust_metadata_rustc_output = rust_metadata_build_output,
             edition = get_edition(ctx.attr, toolchain, ctx.label),
             rustc_env = ctx.attr.rustc_env,
             rustc_env_files = ctx.files.rustc_env_files,
@@ -598,7 +619,7 @@ _common_attrs = {
             The order that these files will be processed is unspecified, so
             multiple definitions of a particular variable are discouraged.
 
-            Note that the variables here are subject to 
+            Note that the variables here are subject to
             [workspace status](https://docs.bazel.build/versions/main/user-manual.html#workspace_status)
             stamping should the `stamp` attribute be enabled. Stamp variables
             should be wrapped in brackets in order to be resolved. E.g.
@@ -611,7 +632,7 @@ _common_attrs = {
             List of compiler flags passed to `rustc`.
 
             These strings are subject to Make variable expansion for predefined
-            source/output path variables like `$location`, `$execpath`, and 
+            source/output path variables like `$location`, `$execpath`, and
             `$rootpath`. This expansion is useful if you wish to pass a generated
             file of arguments to rustc: `@$(location //package:target)`.
         """),
@@ -673,6 +694,9 @@ _common_attrs = {
     "_is_proc_macro_dep_enabled": attr.label(
         default = Label("//:is_proc_macro_dep_enabled"),
     ),
+    "_output_diagnostics": attr.label(
+        default = Label("//:output_diagnostics"),
+    ),
     "_process_wrapper": attr.label(
         doc = "A process wrapper for running rustc on all platforms.",
         default = Label("//util/process_wrapper"),
@@ -723,7 +747,7 @@ _rust_test_attrs = dict({
         mandatory = False,
         default = True,
         doc = dedent("""\
-            Whether to use `libtest`. For targets using this flag, individual tests can be run by using the 
+            Whether to use `libtest`. For targets using this flag, individual tests can be run by using the
             [--test_arg](https://docs.bazel.build/versions/4.0.0/command-line-reference.html#flag--test_arg) flag.
             E.g. `bazel test //src:rust_test --test_arg=foo::test::test_fn`.
         """),

rust/private/rustc.bzl

@@ -52,6 +52,11 @@ ErrorFormatInfo = provider(
     fields = {"error_format": "(string) [" + ", ".join(_error_format_values) + "]"},
 )
 
+OutputDiagnosticsInfo = provider(
+    doc = "Save json diagnostics form rustc",
+    fields = {"output_diagnostics": "(bool)"},
+)
+
 ExtraRustcFlagsInfo = provider(
     doc = "Pass each value as an additional flag to non-exec rustc invocations",
     fields = {"extra_rustc_flags": "List[string] Extra flags to pass to rustc in non-exec configuration"},
@@ -855,6 +860,10 @@ def construct_arguments(
     if build_metadata:
         # Configure process_wrapper to terminate rustc when metadata are emitted
         process_wrapper_flags.add("--rustc-quit-on-rmeta", "true")
+        if crate_info.rust_metadata_rustc_output:
+            process_wrapper_flags.add("--output-file", crate_info.rust_metadata_rustc_output.path)
+    elif crate_info.rust_lib_rustc_output:
+        process_wrapper_flags.add("--output-file", crate_info.rust_lib_rustc_output.path)
 
     rustc_flags.add("--error-format=" + error_format)
 
@@ -1018,6 +1027,8 @@ def rustc_compile_action(
             - (DefaultInfo): The output file for this crate, and its runfiles.
     """
     build_metadata = getattr(crate_info, "metadata", None)
+    rust_lib_rustc_output = getattr(crate_info, "rust_lib_rustc_output", None)
+    rust_metadata_rustc_output = getattr(crate_info, "rust_metadata_rustc_output", None)
 
     cc_toolchain, feature_configuration = find_cc_toolchain(ctx)
 
@@ -1096,7 +1107,7 @@ def rustc_compile_action(
         build_flags_files = build_flags_files,
         force_all_deps_direct = force_all_deps_direct,
         stamp = stamp,
-        use_json_output = bool(build_metadata),
+        use_json_output = bool(build_metadata) or bool(rust_lib_rustc_output) or bool(rust_metadata_rustc_output),
     )
 
     args_metadata = None
@@ -1156,6 +1167,8 @@ def rustc_compile_action(
 
     # The action might generate extra output that we don't want to include in the `DefaultInfo` files.
     action_outputs = list(outputs)
+    if rust_lib_rustc_output:
+        action_outputs.append(rust_lib_rustc_output)
 
     # Rustc generates a pdb file (on Windows) or a dsym folder (on macos) so provide it in an output group for crate
     # types that benefit from having debug information in a separate file.
@@ -1189,7 +1202,7 @@ def rustc_compile_action(
             ctx.actions.run(
                 executable = ctx.executable._process_wrapper,
                 inputs = compile_inputs,
-                outputs = [build_metadata],
+                outputs = [build_metadata] + [x for x in [rust_metadata_rustc_output] if x],
                 env = env,
                 arguments = args_metadata.all,
                 mnemonic = "RustcMetadata",
@@ -1307,12 +1320,24 @@ def rustc_compile_action(
 
     if toolchain.target_arch != "wasm32":
         providers += establish_cc_info(ctx, attr, crate_info, toolchain, cc_toolchain, feature_configuration, interface_library)
+
+    output_group_info = {}
+
     if pdb_file:
-        providers.append(OutputGroupInfo(pdb_file = depset([pdb_file])))
+        output_group_info["pdb_file"] = depset([pdb_file])
     if dsym_folder:
-        providers.append(OutputGroupInfo(dsym_folder = depset([dsym_folder])))
+        output_group_info["dsym_folder"] = depset([dsym_folder])
+    if build_metadata:
+        output_group_info["build_metadata"] = depset([build_metadata])
     if build_metadata:
-        providers.append(OutputGroupInfo(build_metadata = depset([build_metadata])))
+        output_group_info["build_metadata"] = depset([build_metadata])
+        if rust_metadata_rustc_output:
+            output_group_info["rust_metadata_rustc_output"] = depset([rust_metadata_rustc_output])
+    if rust_lib_rustc_output:
+        output_group_info["rust_lib_rustc_output"] = depset([rust_lib_rustc_output])
+
+    if output_group_info:
+        providers.append(OutputGroupInfo(**output_group_info))
 
     return providers
 
@@ -1823,6 +1848,30 @@ error_format = rule(
     build_setting = config.string(flag = True),
 )
 
+def _output_diagnostics_impl(ctx):
+    """Implementation of the `output_diagnostics` rule
+
+    Args:
+        ctx (ctx): The rule's context object
+
+    Returns:
+        list: A list containing the OutputDiagnosticsInfo provider
+    """
+    return [OutputDiagnosticsInfo(output_diagnostics = ctx.build_setting_value)]
+
+output_diagnostics = rule(
+    doc = (
+        "Setting this flag from the command line with `--@rules_rust//:output_diagnostics` " +
+        "makes rules_rust save rustc json output(suitable for consumption by rust-analyzer) in a file. " +
+        "These are accessible via the " +
+        "`rust_metadata_rustc_output`(for pipelined compilation) and `rust_lib_rustc_output` output groups. " +
+        "You can find these either by using something like `find <dir> -name '*.rustc-output'` or by using " +
+        "`bazel cquery --output=files`."
+    ),
+    implementation = _output_diagnostics_impl,
+    build_setting = config.bool(flag = True),
+)
+
 def _extra_rustc_flags_impl(ctx):
     return ExtraRustcFlagsInfo(extra_rustc_flags = ctx.build_setting_value)