[clang] Enforce 1-based indexing for command line source locations

Fixes #139375

Clang expects command line source locations to be provided using
1-based indexing.
Currently, Clang does not reject zero as invalid argument for column
or line number, which can cause Clang to crash.

This commit extends validation in `ParsedSourceLocation::FromString`
to only accept (unsinged) non-zero integers.

Author: naveen-seth

clang/include/clang/Frontend/CommandLineSourceLoc.h

@@ -24,7 +24,9 @@ namespace clang {
 /// A source location that has been parsed on the command line.
 struct ParsedSourceLocation {
   std::string FileName;
+  // The 1-based line number
   unsigned Line;
+  // The 1-based column number
   unsigned Column;
 
 public:
@@ -38,7 +40,8 @@ struct ParsedSourceLocation {
 
     // If both tail splits were valid integers, return success.
     if (!ColSplit.second.getAsInteger(10, PSL.Column) &&
-        !LineSplit.second.getAsInteger(10, PSL.Line)) {
+        !LineSplit.second.getAsInteger(10, PSL.Line) &&
+        !(PSL.Column == 0 || PSL.Line == 0)) {
       PSL.FileName = std::string(LineSplit.first);
 
       // On the command-line, stdin may be specified via "-". Inside the

clang/test/CodeCompletion/crash-if-zero-index.cpp

@@ -0,0 +1,6 @@
+// RUN: not %clang_cc1 -fsyntax-only -code-completion-at=%s:0:1 %s -o -
+// RUN: not %clang_cc1 -fsyntax-only -code-completion-at=%s:1:0 %s -o -
+
+// Related to #139375
+// Clang uses 1-based indexing for source locations given from the command-line.
+// Verify Clang doesn’t crash when 0 is given as line or column number.