[clang-tidy] Enhance modernize-use-starts-ends-with to handle substr patterns

clang-tools-extra/clang-tidy/modernize/UseStartsEndsWithCheck.cpp

@@ -240,6 +240,9 @@ void UseStartsEndsWithCheck::check(const MatchFinder::MatchResult &Result) {
                                        ReplacementFunction->getName());
 
   // Replace arguments and everything after the function call.
+  if (FindExpr->getNumArgs() == 0) {
+    return;
+  }
   Diag << FixItHint::CreateReplacement(
       CharSourceRange::getTokenRange(FindExpr->getArg(0)->getBeginLoc(),
                                      ComparisonExpr->getEndLoc()),
@@ -248,7 +251,6 @@ void UseStartsEndsWithCheck::check(const MatchFinder::MatchResult &Result) {
   // Add negation if necessary.
   if (Neg)
     Diag << FixItHint::CreateInsertion(FindExpr->getBeginLoc(), "!");
-
 }
 
 } // namespace clang::tidy::modernize

clang-tools-extra/docs/clang-tidy/checks/modernize/use-starts-ends-with.rst

@@ -7,7 +7,7 @@ Checks for common roundabout ways to express ``starts_with`` and ``ends_with``
 and suggests replacing with the simpler method when it is available. Notably, 
 this will work with ``std::string`` and ``std::string_view``.
 
-The check handles the following expressions:
+Covered scenarios:
 
 ==================================================== =====================
 Expression                                           Replacement

clang-tools-extra/test/clang-tidy/checkers/modernize/use-starts-ends-with.cpp

@@ -298,6 +298,10 @@ void test_substr() {
     // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead of substr() == [modernize-use-starts-ends-with]
     // CHECK-FIXES: str.starts_with(prefix);
 
+    str.substr(0, prefix.length()) == prefix;
+    // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with instead of substr() == [modernize-use-starts-ends-with]
+    // CHECK-FIXES: str.starts_with(prefix);
+
     // Tests to verify macro behavior
     #define STARTS_WITH(X, Y) (X).substr(0, (Y).size()) == (Y)
     STARTS_WITH(str, prefix);
@@ -308,4 +312,6 @@ void test_substr() {
     #define STR() str
     SUBSTR(STR(), 0, 6) == "prefix";
     "prefix" == SUBSTR(STR(), 0, 6);
+
+    str.substr(0, strlen("hello123")) == "hello";
 }