Fixed exception dispatch idiom not being recognized in the middle of a function.

Author: John Siegel

Diff for: lib/checkexceptionsafety.cpp

@@ -379,21 +379,21 @@ void CheckExceptionSafety::rethrowNoCurrentException()
         if (!function)
             continue;
 
-        // Rethrow can be used in 'exception dispatcher' idiom which is FP in such case
-        // https://isocpp.org/wiki/faq/exceptions#throw-without-an-object
-        // We check the beginning of the function with idiom pattern
-        if (Token::simpleMatch(function->functionScope->bodyStart->next(), "try { throw ; } catch ("))
-            continue;
-
+        //// Rethrow can be used in 'exception dispatcher' idiom which is FP in such case
+        //// https://isocpp.org/wiki/faq/exceptions#throw-without-an-object
+        //// 
+        //// After the idiom is found, continue to the next function scope in the above for loop.
         for (const Token *tok = function->functionScope->bodyStart->next();
-             tok != function->functionScope->bodyEnd; tok = tok->next()) {
+             tok != function->functionScope->bodyEnd && 
+             !Token::simpleMatch(tok, "try { throw ; } catch ("); tok = tok->next()) {
             if (Token::simpleMatch(tok, "catch (")) {
                 tok = tok->linkAt(1);       // skip catch argument
                 if (Token::simpleMatch(tok, ") {"))
                     tok = tok->linkAt(1);   // skip catch scope
                 else
                     break;
             }
+
             if (Token::simpleMatch(tok, "throw ;")) {
                 rethrowNoCurrentExceptionError(tok);
             }

Diff for: test/testexceptionsafety.cpp

@@ -55,6 +55,9 @@ class TestExceptionSafety : public TestFixture {
         TEST_CASE(rethrowNoCurrentException1);
         TEST_CASE(rethrowNoCurrentException2);
         TEST_CASE(rethrowNoCurrentException3);
+        TEST_CASE(exceptionDispatchIdiomInMiddleOfFunction);
+        TEST_CASE(exceptionDispatchIdiomExtraStatements);
+        TEST_CASE(exceptionDispatchIdiomSubsequentRethrows);
     }
 
 #define check(...) check_(__FILE__, __LINE__, __VA_ARGS__)
@@ -449,6 +452,26 @@ class TestExceptionSafety : public TestFixture {
               "void func3() { throw 0; }");
         ASSERT_EQUALS("", errout_str());
     }
+
+    void exceptionDispatchIdiomInMiddleOfFunction() {
+      check("void on_error() { int foo = 5; try { throw; } catch (...) { ; } }");
+      ASSERT_EQUALS("", errout.str());
+
+      check("void on_error() { int foo = 5; try { throw; } catch (const std::exception& e) { ; } }");
+      ASSERT_EQUALS("", errout.str());
+    }
+
+    void exceptionDispatchIdiomExtraStatements() {
+      // extra statements aside from the rethrow should be done before/after the idiom rather than inside it.
+      check("void on_error() { try { int foo = 5; throw; } catch (...) { ; } }");
+      ASSERT_EQUALS("[test.cpp:1]: (error) Rethrowing current exception with 'throw;', it seems there is no current exception to rethrow. If there is no current exception this calls std::terminate(). More: https://isocpp.org/wiki/faq/exceptions#throw-without-an-object\n", errout.str());
+    }
+
+    void exceptionDispatchIdiomSubsequentRethrows() {
+      // if you use the exception dispatch idiom, you have already asserted that you are in a catch block, so subsequent rethrows are valid.
+      check("void on_error() { int foo = 5; try { throw; } catch (...) { ; } throw; }");
+      ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestExceptionSafety)