[llvm] [FileCheck] Fix parsing empty global and pseudo variable names (PR #82595)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-testing-tools

Author: Daniil Kovalev (kovdan01)

<details>
<summary>Changes</summary>

In `Pattern::parseVariable`, for global variables (those starting with '$') and for pseudo variables (those starting with '@') the first character is consumed before actual variable name parsing. If the name is empty, it leads to out-of-bound access to the corresponding `StringRef`.

This patch adds an if statement against the case described.

---
Full diff: https://github.com/llvm/llvm-project/pull/82595.diff


1 Files Affected:

- (modified) llvm/lib/FileCheck/FileCheck.cpp (+6) 


``````````diff
diff --git a/llvm/lib/FileCheck/FileCheck.cpp b/llvm/lib/FileCheck/FileCheck.cpp
index 6d3a2b9cf46f7c..bb1855f599a1a3 100644
--- a/llvm/lib/FileCheck/FileCheck.cpp
+++ b/llvm/lib/FileCheck/FileCheck.cpp
@@ -297,6 +297,12 @@ Pattern::parseVariable(StringRef &Str, const SourceMgr &SM) {
   if (Str[0] == '$' || IsPseudo)
     ++I;
 
+  if (I == Str.size())
+    return ErrorDiagnostic::get(SM, Str,
+                                StringRef("empty ") +
+                                    (IsPseudo ? "pseudo " : "global ") +
+                                    "variable name");
+
   if (!isValidVarNameStart(Str[I++]))
     return ErrorDiagnostic::get(SM, Str, "invalid variable name");
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/82595