[PATCH] D123229: [clang][deps] Ensure deterministic file names on case-insensitive filesystems

Jan Svoboda via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Wed Apr 6 08:52:52 PDT 2022

jansvoboda11 created this revision.
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The dependency scanner can reuse single FileManager instance across multiple translation units. This may lead to non-deterministic output depending on which TU gets processed first.

The root cause is the fact that Clang is using DirectoryEntry::getName in the header search algorithm. This function returns the path that was first used to construct the (shared) entry in FileManager. Using DirectoryEntryRef::getName instead preserves the case as it was spelled out for the current "get directory entry" request.


  rG LLVM Github Monorepo



Index: clang/test/ClangScanDeps/header-search-case-sensitivity.c
--- /dev/null
+++ clang/test/ClangScanDeps/header-search-case-sensitivity.c
@@ -0,0 +1,50 @@
+// This test checks that
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+//--- dir1/arm/lower.h
+//--- dir2/ARM/upper.h
+//--- t1.c
+#include "upper.h"
+//--- t2.c
+#include "arm/lower.h"
+//--- cdb.json.template
+  "directory": "DIR",
+  "command": "clang -fsyntax-only DIR/t1.c -I DIR/dir2/ARM -I DIR/dir1",
+  "file": "DIR/t1.c"
+  "directory": "DIR",
+  "command": "clang -fsyntax-only DIR/t2.c -I DIR/dir2     -I DIR/dir1",
+  "file": "DIR/t2.c"
+//--- cdb-rev.json.template
+  "directory": "DIR",
+  "command": "clang -fsyntax-only DIR/t2.c -I DIR/dir2     -I DIR/dir1",
+  "file": "DIR/t2.c"
+  "directory": "DIR",
+  "command": "clang -fsyntax-only DIR/t1.c -I DIR/dir2/ARM -I DIR/dir1",
+  "file": "DIR/t1.c"
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.template     > %t/cdb.json
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb-rev.json.template > %t/cdb-rev.json
+// RUN: clang-scan-deps -compilation-database=%t/cdb.json     -format make -j 1 | FileCheck %s
+// In the reversed case, Clang starts by scanning "t2.c". When looking up the "arm/lower.h" header,
+// the string is appended to "DIR/dir2". That file ("DIR/dir2/arm/lower.h") doesn't exist, but when
+// learning so, the FileManager stats and caches the parent directory ("DIR/dir2/arm"), using the
+// UID as the key.
+// When scanning "t1.c" later on, the "DIR/dir2/ARM" search directory is assigned the **same**
+// directory entry (with lowercase "arm"), since they share the UID on case-insensitive filesystems.
+// To preserve the correct case throughout the compiler for any file within that directory, it's
+// important to use the spelling actually used, not just the cached one.
+// RUN: clang-scan-deps -compilation-database=%t/cdb-rev.json -format make -j 1 | FileCheck %s
+// CHECK: ARM/upper.h
Index: clang/lib/Lex/HeaderSearch.cpp
--- clang/lib/Lex/HeaderSearch.cpp
+++ clang/lib/Lex/HeaderSearch.cpp
@@ -436,10 +436,10 @@
   SmallString<1024> TmpDir;
   if (isNormalDir()) {
     // Concatenate the requested file onto the directory.
-    TmpDir = getDir()->getName();
+    TmpDir = getDirRef()->getName();
     llvm::sys::path::append(TmpDir, Filename);
     if (SearchPath) {
-      StringRef SearchPathRef(getDir()->getName());
+      StringRef SearchPathRef(getDirRef()->getName());
       SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
Index: clang/include/clang/Lex/DirectoryLookup.h
--- clang/include/clang/Lex/DirectoryLookup.h
+++ clang/include/clang/Lex/DirectoryLookup.h
@@ -91,6 +91,10 @@
     return isNormalDir() ? &u.Dir.getDirEntry() : nullptr;
+  Optional<DirectoryEntryRef> getDirRef() const {
+    return isNormalDir() ? Optional<DirectoryEntryRef>(u.Dir) : None;
+  }
   /// getFrameworkDir - Return the directory that this framework refers to.
   const DirectoryEntry *getFrameworkDir() const {

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