Added GetRunfilesDir() to be able to reliably determine prelude location under various invocation scenarios

explorer/fuzzing/BUILD

@@ -25,11 +25,13 @@ cc_library(
     hdrs = ["fuzzer_util.h"],
     deps = [
         "//common:check",
+        "//common:error",
         "//common/fuzzing:carbon_cc_proto",
         "//common/fuzzing:proto_to_carbon_lib",
         "//explorer/interpreter:exec_program",
         "//explorer/syntax",
         "//explorer/syntax:prelude",
+        "@bazel_tools//tools/cpp/runfiles",
         "@com_google_protobuf//:protobuf_headers",
         "@llvm-project//llvm:Support",
     ],

explorer/fuzzing/fuzzer_util.cpp

@@ -9,7 +9,10 @@
 #include "explorer/interpreter/exec_program.h"
 #include "explorer/syntax/parse.h"
 #include "explorer/syntax/prelude.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
+#include "tools/cpp/runfiles/runfiles.h"
 
 namespace Carbon {
 
@@ -21,6 +24,23 @@ fn Main() -> i32 {
 }
 )";
 
+auto Internal::GetRunfilesFile(const std::string& file)
+    -> ErrorOr<std::string> {
+  using bazel::tools::cpp::runfiles::Runfiles;
+  std::string error;
+  // `Runfiles::Create()` fails if passed an empty `argv0`.
+  std::unique_ptr<Runfiles> runfiles(Runfiles::Create(
+      /*argv0=*/llvm::sys::fs::getMainExecutable(nullptr, nullptr), &error));
+  if (runfiles == nullptr) {
+    return Error(error);
+  }
+  std::string full_path = runfiles->Rlocation(file);
+  if (!llvm::sys::fs::exists(full_path)) {
+    return ErrorBuilder() << full_path << " doesn't exist";
+  }
+  return full_path;
+}
+
 auto ProtoToCarbonWithMain(const Fuzzing::CompilationUnit& compilation_unit)
     -> std::string {
   const bool has_main = std::any_of(
@@ -43,7 +63,10 @@ void ParseAndExecute(const Fuzzing::CompilationUnit& compilation_unit) {
     llvm::errs() << "Parsing failed: " << ast.error().message() << "\n";
     return;
   }
-  AddPrelude("explorer/data/prelude.carbon", &arena, &ast->declarations);
+  const ErrorOr<std::string> prelude_path =
+      Internal::GetRunfilesFile("carbon/explorer/data/prelude.carbon");
+  CHECK(prelude_path.ok()) << prelude_path.error().message();
+  AddPrelude(*prelude_path, &arena, &ast->declarations);
   const ErrorOr<int> result =
       ExecProgram(&arena, *ast, /*trace_stream=*/std::nullopt);
   if (!result.ok()) {

explorer/fuzzing/fuzzer_util.h

@@ -5,6 +5,7 @@
 #ifndef EXPLORER_FUZZING_FUZZER_UTIL_H_
 #define EXPLORER_FUZZING_FUZZER_UTIL_H_
 
+#include "common/error.h"
 #include "common/fuzzing/carbon.pb.h"
 
 namespace Carbon {
@@ -17,6 +18,13 @@ auto ProtoToCarbonWithMain(const Fuzzing::CompilationUnit& compilation_unit)
 // Parses and executes a fuzzer-generated program.
 void ParseAndExecute(const Fuzzing::CompilationUnit& compilation_unit);
 
+namespace Internal {
+
+// Returns a full path for a file under bazel runfiles.
+// Exposed for testing.
+auto GetRunfilesFile(const std::string& file) -> ErrorOr<std::string>;
+
+}  // namespace Internal
 }  // namespace Carbon
 
 #endif  // EXPLORER_FUZZING_FUZZER_UTIL_H_

explorer/fuzzing/fuzzer_util_test.cpp

@@ -36,6 +36,19 @@ TEST(FuzzerUtilTest, RunFuzzerOnCorpus) {
   EXPECT_GT(file_count, 0);
 }
 
+TEST(FuzzerUtilTest, GetRunfilesFile) {
+  EXPECT_THAT(*Internal::GetRunfilesFile(
+                  "carbon/explorer/fuzzing/fuzzer_corpus/empty.textproto"),
+              testing::EndsWith("/explorer/fuzzing/fuzzer_corpus/"
+                                "empty.textproto"));
+  EXPECT_THAT(Internal::GetRunfilesFile(
+                  "explorer/fuzzing/fuzzer_corpus/empty.textproto")
+                  .error()
+                  .message(),
+              testing::EndsWith("fuzzer_util_test.runfiles/explorer/fuzzing/"
+                                "fuzzer_corpus/empty.textproto doesn't exist"));
+}
+
 }  // namespace
 }  // namespace Carbon::Testing
 

scripts/fix_cc_deps.py

@@ -36,6 +36,9 @@
     "@com_google_libprotobuf_mutator": lambda x: re.sub(
         "^(.*:)", "libprotobuf_mutator/", x
     ),
+    # @bazel_tools//tools/cpp/runfiles:runfiles.h ->
+    #   tools/cpp/runfiles/runfiles.h
+    "@bazel_tools": lambda x: re.sub(":", "/", x),
 }
 
 # TODO: proto rules are aspect-based and their generated files don't show up in