Add bool config setting to enable diagnostic output

Author: googleson78

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(

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/rust.bzl

@@ -64,9 +64,8 @@ def _assert_correct_dep_mapping(ctx):
                 ),
             )
 
-
 def _rustc_output_name(name):
-  return name + ".rustc-output"
+    return name + ".rustc-output"
 
 def _determine_lib_name(name, crate_type, toolchain, lib_hash = None):
     """See https://github.com/bazelbuild/rules_rust/issues/405
@@ -282,7 +281,8 @@ def _rust_library_common(ctx, crate_type):
 
     rust_lib = ctx.actions.declare_file(rust_lib_name)
     rust_lib_build_output = None
-    if ctx.attr._process_wrapper:
+    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))
 
     rust_metadata = None
@@ -294,7 +294,8 @@ def _rust_library_common(ctx, crate_type):
             rust_metadata_name,
             sibling = rust_lib,
         )
-        rust_metadata_build_output = ctx.actions.declare_file(_rustc_output_name(rust_metadata_name))
+        if output_diagnostics:
+            rust_metadata_build_output = ctx.actions.declare_file(_rustc_output_name(rust_metadata_name))
 
     deps = transform_deps(ctx.attr.deps)
     proc_macro_deps = transform_deps(ctx.attr.proc_macro_deps + get_import_macro_deps(ctx))
@@ -665,6 +666,9 @@ _common_attrs = {
     "_error_format": attr.label(
         default = Label("//:error_format"),
     ),
+    "_output_diagnostics": attr.label(
+        default = Label("//:output_diagnostics"),
+    ),
     "_extra_exec_rustc_flag": attr.label(
         default = Label("//:extra_exec_rustc_flag"),
     ),

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"},
@@ -857,10 +862,8 @@ def construct_arguments(
         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)
-    else:
-        if crate_info.rust_lib_rustc_output:
-            process_wrapper_flags.add("--output-file", crate_info.rust_lib_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)
 
@@ -1104,7 +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
@@ -1844,6 +1847,30 @@ 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)