[clang-format] Fix crash involving array designators

[XDeme1]

Fixes #76716
Fixes parsing of [0]{}. Before this patch it was begin parsed as a lambda, now it is correctly parsed as a designator initializer.

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: None (XDeme)

Changes

Fixes llvm/llvm-project#76716
Added a check to prevent null deferencing

---

Full diff: https://github.com/llvm/llvm-project/pull/77045.diff

2 Files Affected:

• (modified) clang/lib/Format/WhitespaceManager.cpp (+2-1)
• (modified) clang/unittests/Format/FormatTest.cpp (+6)

diff --git a/clang/lib/Format/WhitespaceManager.cpp b/clang/lib/Format/WhitespaceManager.cpp
index 3bc6915b8df0a7..95693f4588c631 100644
--- a/clang/lib/Format/WhitespaceManager.cpp
+++ b/clang/lib/Format/WhitespaceManager.cpp
@@ -1444,7 +1444,8 @@ WhitespaceManager::CellDescriptions WhitespaceManager::getCells(unsigned Start,
       } else if (C.Tok->is(tok::comma)) {
         if (!Cells.empty())
           Cells.back().EndIndex = i;
-        if (C.Tok->getNextNonComment()->isNot(tok::r_brace)) // dangling comma
+        const FormatToken *Next = C.Tok->getNextNonComment();
+        if (Next && Next->isNot(tok::r_brace)) // dangling comma
           ++Cell;
       }
     } else if (Depth == 1) {
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 881993ede17c3d..c9f91953c13f52 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -21084,6 +21084,12 @@ TEST_F(FormatTest, CatchAlignArrayOfStructuresLeftAlignment) {
       "};",
       Style);
 
+  verifyNoCrash("Foo f[] = {\n"
+                "    [0] = { 1, },\n"
+                "    [1] { 1, },\n"
+                "};",
+                Style);
+
   verifyFormat("return GradForUnaryCwise(g, {\n"
                "                                {{\"sign\"}, \"Sign\", {\"x\", "
                "\"dy\"}   },\n"

[XDeme1]

While I was trying to find a minimal reproducer to the bug, I accidentally found that this patch fix another crash, and doesn't fix the linked issue.

[XDeme1]

I think with this the issue might be fixed.

[owenca]

Please add an assertion in WhitespaceManager.h:

--- a/clang/lib/Format/WhitespaceManager.h
+++ b/clang/lib/Format/WhitespaceManager.h
@@ -282,6 +282,7 @@ private:
     for (auto PrevIter = Start; PrevIter != End; ++PrevIter) {
       // If we broke the line the initial spaces are already
       // accounted for.
+      assert(PrevIter->Index) < Changes.size();
       if (Changes[PrevIter->Index].NewlinesBefore > 0)
         NetWidth = 0;
       NetWidth +=

[owenca]

While I was trying to find a minimal reproducer to the bug, I accidentally found that this patch fix another crash, and doesn't fix the linked issue.

Can you open another pull request to fix the other crash?

[XDeme1]

While I was trying to find a minimal reproducer to the bug, I accidentally found that this patch fix another crash, and doesn't fix the linked issue.

Can you open another pull request to fix the other crash?

@owenca Just created #77723