fix: Improve Unicode normalization and add regex metachar tests (#44944)

Enhanced SanitizeAndNormalize to handle Unicode normalization more
robustly, ensuring correct buffer sizing and error handling. Added unit
tests for regex metacharacters `$` and `^` to verify correct replacement
behavior at string boundaries. Improves Unicode support and test
coverage for regex edge cases.

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## Summary of the Pull Request

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- [x] Closes: #44942 #44892
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---------

Co-authored-by: Yu Leng <yuleng@microsoft.com>

.github/actions/spell-check/expect.txt

@@ -1011,6 +1011,7 @@ MENUITEMINFO
 MENUITEMINFOW
 MERGECOPY
 MERGEPAINT
+Metacharacter
 metadatamatters
 Metadatas
 metafile

src/modules/powerrename/lib/PowerRenameRegEx.cpp

@@ -33,23 +33,27 @@ static std::wstring SanitizeAndNormalize(const std::wstring& input)
 
     // Normalize to NFC (Precomposed).
     // Get the size needed for the normalized string, including null terminator.
-    int size = NormalizeString(NormalizationC, sanitized.c_str(), -1, nullptr, 0);
+    int sizeEstimate = NormalizeString(NormalizationC, sanitized.c_str(), -1, nullptr, 0);
-    if (size <= 0)
+    if (sizeEstimate <= 0)
     {
         return sanitized; // Return unaltered if normalization fails.
     }
 
     // Perform the normalization.
     std::wstring normalized;
-    normalized.resize(size);
+    normalized.resize(sizeEstimate);
-    NormalizeString(NormalizationC, sanitized.c_str(), -1, &normalized[0], size);
+    int actualSize = NormalizeString(NormalizationC, sanitized.c_str(), -1, &normalized[0], sizeEstimate);
 
-    // Remove the explicit null terminator added by NormalizeString.
+    if (actualSize <= 0)
-    if (!normalized.empty() && normalized.back() == L'\0')
     {
-        normalized.pop_back();
+        // Normalization failed, return sanitized string.
+        return sanitized;
     }
 
+    // Resize to actual size minus the null terminator.
+    // actualSize includes the null terminator when input length is -1.
+    normalized.resize(static_cast<size_t>(actualSize) - 1);
+
     return normalized;
 }
 

src/modules/powerrename/unittests/CommonRegExTests.h

@@ -695,6 +695,38 @@ TEST_METHOD(VerifyUnicodeAndWhitespaceNormalizationRegex)
     VerifyNormalizationHelper(UseRegularExpressions);
 }
 
+TEST_METHOD(VerifyRegexMetacharacterDollarSign)
+{
+    CComPtr<IPowerRenameRegEx> renameRegEx;
+    Assert::IsTrue(CPowerRenameRegEx::s_CreateInstance(&renameRegEx) == S_OK);
+    DWORD flags = UseRegularExpressions;
+    Assert::IsTrue(renameRegEx->PutFlags(flags) == S_OK);
+
+    PWSTR result = nullptr;
+    Assert::IsTrue(renameRegEx->PutSearchTerm(L"$") == S_OK);
+    Assert::IsTrue(renameRegEx->PutReplaceTerm(L"_end") == S_OK);
+    unsigned long index = {};
+    Assert::IsTrue(renameRegEx->Replace(L"test.txt", &result, index) == S_OK);
+    Assert::AreEqual(L"test.txt_end", result);
+    CoTaskMemFree(result);
+}
+
+TEST_METHOD(VerifyRegexMetacharacterCaret)
+{
+    CComPtr<IPowerRenameRegEx> renameRegEx;
+    Assert::IsTrue(CPowerRenameRegEx::s_CreateInstance(&renameRegEx) == S_OK);
+    DWORD flags = UseRegularExpressions;
+    Assert::IsTrue(renameRegEx->PutFlags(flags) == S_OK);
+
+    PWSTR result = nullptr;
+    Assert::IsTrue(renameRegEx->PutSearchTerm(L"^") == S_OK);
+    Assert::IsTrue(renameRegEx->PutReplaceTerm(L"start_") == S_OK);
+    unsigned long index = {};
+    Assert::IsTrue(renameRegEx->Replace(L"test.txt", &result, index) == S_OK);
+    Assert::AreEqual(L"start_test.txt", result);
+    CoTaskMemFree(result);
+}
+
 #ifndef TESTS_PARTIAL
 };
 }