[clang] Implement setting crash_diagnostics_dir through env variable

This implements setting the equivalent of `-fcrash-diagnostics-dir`
through the environment variable `CLANG_CRASH_DIAGNOSTICS_DIR`.
If present, the flag still takes precedence.

This helps integration with test frameworks and pipelines.

With this feature, we change the libcxx bootstrapping build
pipeline to produce clang crash reproducers as artifacts.

Signed-off-by: Matheus Izvekov <[email protected]>

Differential Revision: https://reviews.llvm.org/D133082

Author: mizvekov

clang/docs/ReleaseNotes.rst

@@ -135,6 +135,9 @@ Improvements to Clang's diagnostics
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
+- It's now possible to set the crash diagnostics directory through
+  the environment variable ``CLANG_CRASH_DIAGNOSTICS_DIR``.
+  The ``-fcrash-diagnostics-dir`` flag takes precedence.
 
 New Compiler Flags
 ------------------

clang/docs/UsersManual.rst

@@ -687,6 +687,11 @@ of generating a delta reduced test case.
   Specify where to write the crash diagnostics files; defaults to the
   usual location for temporary files.
 
+.. envvar:: CLANG_CRASH_DIAGNOSTICS_DIR=<dir>
+
+   Like :option:`-fcrash-diagnostics-dir=<dir>`, specifies where to write the
+   crash diagnostics files, but with lower precedence than the option.
+
 Clang is also capable of generating preprocessed source file(s) and associated
 run script(s) even without a crash. This is specially useful when trying to
 generate a reproducer for warnings or errors while using modules.

clang/lib/Driver/Driver.cpp

@@ -5413,15 +5413,18 @@ const char *Driver::CreateTempFile(Compilation &C, StringRef Prefix,
                                    StringRef BoundArch) const {
   SmallString<128> TmpName;
   Arg *A = C.getArgs().getLastArg(options::OPT_fcrash_diagnostics_dir);
-  if (CCGenDiagnostics && A) {
-    SmallString<128> CrashDirectory(A->getValue());
-    if (!getVFS().exists(CrashDirectory))
-      llvm::sys::fs::create_directories(CrashDirectory);
-    llvm::sys::path::append(CrashDirectory, Prefix);
+  Optional<std::string> CrashDirectory =
+      CCGenDiagnostics && A
+          ? std::string(A->getValue())
+          : llvm::sys::Process::GetEnv("CLANG_CRASH_DIAGNOSTICS_DIR");
+  if (CrashDirectory) {
+    if (!getVFS().exists(*CrashDirectory))
+      llvm::sys::fs::create_directories(*CrashDirectory);
+    SmallString<128> Path(*CrashDirectory);
+    llvm::sys::path::append(Path, Prefix);
     const char *Middle = !Suffix.empty() ? "-%%%%%%." : "-%%%%%%";
-    std::error_code EC = llvm::sys::fs::createUniqueFile(
-        CrashDirectory + Middle + Suffix, TmpName);
-    if (EC) {
+    if (std::error_code EC =
+            llvm::sys::fs::createUniqueFile(Path + Middle + Suffix, TmpName)) {
       Diag(clang::diag::err_unable_to_make_temp) << EC.message();
       return "";
     }

clang/test/Driver/crash-diagnostics-dir-3.c

@@ -0,0 +1,5 @@
+// RUN: rm -rf %t
+// RUN: not env CLANG_CRASH_DIAGNOSTICS_DIR=%t %clang -c %s -o - 2>&1 | FileCheck %s
+#pragma clang __debug parser_crash
+// CHECK: Preprocessed source(s) and associated run script(s) are located at:
+// CHECK: diagnostic msg: {{.*}}{{/|\\}}crash-diagnostics-dir-3.c.tmp{{(/|\\).*}}.c

libcxx/utils/ci/buildkite-pipeline.yml

@@ -369,10 +369,12 @@ steps:
     artifact_paths:
       - "**/test-results.xml"
       - "**/*.abilist"
+      - "**/crash_diagnostics/*"
     env:
         CC: "clang-${LLVM_HEAD_VERSION}"
         CXX: "clang++-${LLVM_HEAD_VERSION}"
         LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}"
+        CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
     agents:
       queue: "libcxx-builders"
       os: "linux"