[clang-tidy] Fix PR35824

Differential Revision: https://reviews.llvm.org/D46027

Author: Xazax-hun

clang-tools-extra/clang-tidy/bugprone/SuspiciousSemicolonCheck.cpp

@@ -20,7 +20,8 @@ namespace bugprone {
 void SuspiciousSemicolonCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       stmt(anyOf(ifStmt(hasThen(nullStmt().bind("semi")),
-                        unless(hasElse(stmt()))),
+                        unless(hasElse(stmt())),
+                        unless(isConstexpr())),
                  forStmt(hasBody(nullStmt().bind("semi"))),
                  cxxForRangeStmt(hasBody(nullStmt().bind("semi"))),
                  whileStmt(hasBody(nullStmt().bind("semi")))))

clang-tools-extra/test/clang-tidy/bugprone-suspicious-semicolon-constexpr.cpp

@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy %s bugprone-suspicious-semicolon %t -- -- -std=c++17
+
+void fail()
+{
+  int x = 0;
+  if(x > 5); (void)x;
+  // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: potentially unintended semicolon [bugprone-suspicious-semicolon]
+  // CHECK-FIXES: if(x > 5) (void)x;
+}
+
+template <int X>
+int foo(int a) {
+    if constexpr(X > 0) {
+        return a;
+    }
+    return a + 1;
+}
+
+template <int X>
+int foo2(int a) {
+    // FIXME: diagnose the case below. See https://reviews.llvm.org/D46234
+    // for details.
+    if constexpr(X > 0);
+        return a;
+    return a + 1;
+}
+
+int main(void) {
+    foo2<0>(1);
+    return foo<0>(1);
+}