Add mojo fixit support (#75)

This is experimental but can be enabled with
`--@rules_mojo//:experimental_export_fixits
--output_groups=+mojo_fixits` and then you can process the produced yaml
files with clang-apply-replacements

Author: keith

BUILD.bazel

@@ -1,3 +1,4 @@
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 load("//mojo:build_settings.bzl", "repeatable_string_flag")
 
 repeatable_string_flag(
@@ -21,3 +22,9 @@ toolchain_type(
     name = "gpu_toolchain_type",
     visibility = ["//visibility:public"],
 )
+
+bool_flag(
+    name = "experimental_export_fixits",
+    build_setting_default = False,
+    visibility = ["//visibility:public"],
+)

mojo/mojo_library.bzl

@@ -32,13 +32,21 @@ def _mojo_library_implementation(ctx):
         if not file.dirname.startswith(root_directory):
             args.add_all([file], map_each = _format_include)
 
+    output_group_kwargs = {}
+    package_outputs = [mojo_package]
+    if ctx.attr._export_fixits[BuildSettingInfo].value:
+        fixits_file = ctx.actions.declare_file(ctx.label.name + ".mojo_fixits.yaml")
+        package_outputs.append(fixits_file)
+        output_group_kwargs["mojo_fixits"] = depset([fixits_file])
+        args.add("--experimental-export-fixit", fixits_file)
+
     file_args.add_all(transitive_mojopkgs, map_each = _format_include)
     file_args.add(root_directory)
     ctx.actions.run(
         executable = mojo_toolchain.mojo,
         inputs = depset(ctx.files.srcs + ctx.files.additional_compiler_inputs, transitive = [transitive_mojopkgs]),
         tools = mojo_toolchain.all_tools,
-        outputs = [mojo_package],
+        outputs = package_outputs,
         arguments = [args, file_args],
         mnemonic = "MojoPackage",
         progress_message = "%{label} building mojo package",
@@ -67,6 +75,7 @@ def _mojo_library_implementation(ctx):
             import_paths = depset([mojo_package.dirname], transitive = [import_paths]),
             mojopkgs = depset([mojo_package], transitive = [transitive_mojopkgs]),
         ),
+        OutputGroupInfo(**output_group_kwargs),
     ]
 
 mojo_library = rule(
@@ -104,6 +113,9 @@ package' since it does not accept many flags.
         "_mojo_package_copts": attr.label(
             default = Label("//:mojo_package_copt"),
         ),
+        "_export_fixits": attr.label(
+            default = Label("@rules_mojo//:experimental_export_fixits"),
+        ),
     },
     toolchains = ["//:toolchain_type"],
 )

mojo/private/mojo_binary_test.bzl

@@ -52,6 +52,9 @@ This is useful for shared sanitizer libraries which need to have rpaths added
 by bazel.
 """,
     ),
+    "_export_fixits": attr.label(
+        default = Label("@rules_mojo//:experimental_export_fixits"),
+    ),
 }
 
 _TOOLCHAINS = use_cpp_toolchain() + [
@@ -128,11 +131,19 @@ def _mojo_binary_test_implementation(ctx, *, shared_library = False):
     if ctx.attr.enable_assertions:
         args.add("-D", "ASSERT=all")
 
+    output_group_kwargs = {}
+    compile_outputs = [object_file]
+    if ctx.attr._export_fixits[BuildSettingInfo].value:
+        fixits_file = ctx.actions.declare_file(ctx.label.name + ".mojo_fixits.yaml")
+        compile_outputs.append(fixits_file)
+        output_group_kwargs["mojo_fixits"] = depset([fixits_file])
+        args.add("--experimental-export-fixit", fixits_file)
+
     ctx.actions.run(
         executable = mojo_toolchain.mojo,
         tools = mojo_toolchain.all_tools,
         inputs = depset(ctx.files.srcs + ctx.files.additional_compiler_inputs, transitive = [transitive_mojopkgs]),
-        outputs = [object_file],
+        outputs = compile_outputs,
         arguments = [args],
         mnemonic = "MojoCompile",
         progress_message = "%{label} compiling mojo object",
@@ -267,6 +278,7 @@ def _mojo_binary_test_implementation(ctx, *, shared_library = False):
                     ]),
                 ),
             ),
+            OutputGroupInfo(**output_group_kwargs),
         ]
     else:
         return [
@@ -277,6 +289,7 @@ def _mojo_binary_test_implementation(ctx, *, shared_library = False):
             RunEnvironmentInfo(
                 environment = runtime_env,
             ),
+            OutputGroupInfo(**output_group_kwargs),
         ]
 
 mojo_binary = rule(

tests/fixits/BUILD.bazel

@@ -0,0 +1,19 @@
+load("//mojo:mojo_binary.bzl", "mojo_binary")
+load("//mojo:mojo_library.bzl", "mojo_library")
+
+# TODO: Find a fixit that doesn't fail the build, verify the output file
+
+mojo_binary(
+    name = "fixits",
+    srcs = ["fixits.mojo"],
+    tags = ["manual"],
+)
+
+mojo_library(
+    name = "package",
+    srcs = [
+        "package/__init__.mojo",
+        "package/package.mojo",
+    ],
+    tags = ["manual"],
+)

tests/fixits/fixits.mojo

@@ -0,0 +1,5 @@
+fn old_origin_of[T: AnyType](b: T):
+    _ = __origin_of(b)
+
+fn main():
+    pass

tests/fixits/package/__init__.mojo

@@ -0,0 +1,2 @@
+fn old_origin_of[T: AnyType](b: T):
+    _ = __origin_of(b)