[clang-format][PR41964] Fix crash with SIGFPE when TabWidth is set to 0 and line starts with tab

Summary:
clang-format 8.0 crashes with SIGFPE (floating point exception) when formatting following file:
app.cpp:
void a() {
	//line starts with '\t'
}

$ clang-format -style='{TabWidth: 0}' app.cpp

Reviewers: owenpan, klimek, russellmcc, timwoj

Reviewed By: klimek

Subscribers: cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D67670

llvm-svn: 372246

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Format/Encoding.h b/clang/lib/Format/Encoding.h
index fe3d5f01985..a0d664121b2 100644
--- a/clang/lib/Format/Encoding.h
+++ b/clang/lib/Format/Encoding.h
@@ -67,7 +67,8 @@ inline unsigned columnWidthWithTabs(StringRef Text, unsigned StartColumn,
     if (TabPos == StringRef::npos)
       return TotalWidth + columnWidth(Tail, Encoding);
     TotalWidth += columnWidth(Tail.substr(0, TabPos), Encoding);
-    TotalWidth += TabWidth - (TotalWidth + StartColumn) % TabWidth;
+    if (TabWidth)
+      TotalWidth += TabWidth - (TotalWidth + StartColumn) % TabWidth;
     Tail = Tail.substr(TabPos + 1);
   }
 }