[clang-tidy] modernize-use-starts-ends-with: fix false positives on find and rfind (#129564)

Also document cases with two or three arguments (matching default arguments)
this check matches.

Closes #129498.

Author: vbvictor

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

@@ -113,21 +113,33 @@ void UseStartsEndsWithCheck::registerMatchers(MatchFinder *Finder) {
   const auto OnClassWithEndsWithFunction = ClassTypeWithMethod(
       "ends_with_fun", "ends_with", "endsWith", "endswith", "EndsWith");
 
-  // Case 1: X.find(Y) [!=]= 0 -> starts_with.
+  // Case 1: X.find(Y, [0], [LEN(Y)]) [!=]= 0 -> starts_with.
   const auto FindExpr = cxxMemberCallExpr(
-      anyOf(argumentCountIs(1), hasArgument(1, ZeroLiteral)),
       callee(
           cxxMethodDecl(hasName("find"), ofClass(OnClassWithStartsWithFunction))
               .bind("find_fun")),
-      hasArgument(0, expr().bind("needle")));
-
-  // Case 2: X.rfind(Y, 0) [!=]= 0 -> starts_with.
+      hasArgument(0, expr().bind("needle")),
+      anyOf(
+          // Detect the expression: X.find(Y);
+          argumentCountIs(1),
+          // Detect the expression: X.find(Y, 0);
+          allOf(argumentCountIs(2), hasArgument(1, ZeroLiteral)),
+          // Detect the expression: X.find(Y, 0, LEN(Y));
+          allOf(argumentCountIs(3), hasArgument(1, ZeroLiteral),
+                hasArgument(2, lengthExprForStringNode("needle")))));
+
+  // Case 2: X.rfind(Y, 0, [LEN(Y)]) [!=]= 0 -> starts_with.
   const auto RFindExpr = cxxMemberCallExpr(
-      hasArgument(1, ZeroLiteral),
       callee(cxxMethodDecl(hasName("rfind"),
                            ofClass(OnClassWithStartsWithFunction))
                  .bind("find_fun")),
-      hasArgument(0, expr().bind("needle")));
+      hasArgument(0, expr().bind("needle")),
+      anyOf(
+          // Detect the expression: X.rfind(Y, 0);
+          allOf(argumentCountIs(2), hasArgument(1, ZeroLiteral)),
+          // Detect the expression: X.rfind(Y, 0, LEN(Y));
+          allOf(argumentCountIs(3), hasArgument(1, ZeroLiteral),
+                hasArgument(2, lengthExprForStringNode("needle")))));
 
   // Case 3: X.compare(0, LEN(Y), Y) [!=]= 0 -> starts_with.
   const auto CompareExpr = cxxMemberCallExpr(

clang-tools-extra/docs/ReleaseNotes.rst

@@ -175,6 +175,11 @@ Changes in existing checks
   <clang-tidy/checks/modernize/use-ranges>` check by updating suppress 
   warnings logic for ``nullptr`` in ``std::find``.
 
+- Improved :doc:`modernize-use-starts-ends-with
+  <clang-tidy/checks/modernize/use-starts-ends-with>` check by adding more
+  matched scenarios of ``find`` and ``rfind`` methods and fixing false
+  positives when those methods were called with 3 arguments.
+
 - Improved :doc:`modernize-use-std-numbers
   <clang-tidy/checks/modernize/use-std-numbers>` check to support math
   functions of different precisions.

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

@@ -13,7 +13,10 @@ Covered scenarios:
 Expression                                           Replacement
 ---------------------------------------------------- ---------------------
 ``u.find(v) == 0``                                   ``u.starts_with(v)``
+``u.find(v, 0) == 0``                                ``u.starts_with(v)``
+``u.find(v, 0, v.size()) == 0``                      ``u.starts_with(v)``
 ``u.rfind(v, 0) != 0``                               ``!u.starts_with(v)``
+``u.rfind(v, 0, v.size()) != 0``                     ``!u.starts_with(v)``
 ``u.compare(0, v.size(), v) == 0``                   ``u.starts_with(v)``
 ``u.substr(0, v.size()) == v``                       ``u.starts_with(v)``
 ``v != u.substr(0, v.size())``                       ``!u.starts_with(v)``

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

@@ -236,6 +236,42 @@ void test(std::string s, std::string_view sv, sub_string ss, sub_sub_string sss,
   // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use ends_with
   // CHECK-FIXES: s.ends_with(suffix);
 
+  s.find("a", 0) == 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with("a");
+
+  s.find(s, ZERO) == 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with(s);
+
+  s.find(s, 0) == ZERO;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with(s);
+
+  s.find("aaa", 0, 3) == 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with("aaa");
+
+  s.find("aaa", ZERO, 3) == 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with("aaa");
+
+  s.find("aaa", ZERO, strlen(("aaa"))) == ZERO;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with("aaa");
+
+  s.rfind("aaa", 0, 3) != 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: !s.starts_with("aaa");
+
+  s.rfind("aaa", ZERO, 3) != 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: !s.starts_with("aaa");
+
+  s.rfind("aaa", ZERO, strlen(("aaa"))) == ZERO;
+  // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: use starts_with
+  // CHECK-FIXES: s.starts_with("aaa");
+
   struct S {
     std::string s;
   } t;
@@ -261,6 +297,12 @@ void test(std::string s, std::string_view sv, sub_string ss, sub_sub_string sss,
 
   #define STRING s
   if (0 == STRING.find("ala")) { /* do something */}
+
+  // Cases when literal-size and size parameters are different are not being matched.
+  s.find("aaa", 0, 2) == 0;
+  s.find("aaa", 0, strlen("aa")) == 0;
+  s.rfind("aaa", 0, 2) == 0;
+  s.rfind("aaa", 0, strlen("aa")) == 0;
 }
 
 void test_substr() {