Bug 8788 – The super constructor call can be prevented by mentioning "return".

Mentioning a "return" prevents DMD from rejecting code where a constructor has an explicit super() call which is done conditionally or not at all. Also it is possible to return or throw before doing the super() call. This example code compiles although it should be rejected: --- class A { this ( ) { } } class B : A { this ( ) { return; super(); } this(int x) { try { throw new Exception; super(); } catch ( ) { } } this(float f) { if (x == 3) return; else super(); } this(char c) { if (c == 'x') super(); else return; } } --- However, if the "return" statement in the second and third constructor is omitted, the compile error is triggered correctly.

Of course the "if" condition in the third constructor should be f >= 3, not x == 3.

statement.c, ReturnStatement::semantic() contains this comment: /* BUG: need to issue an error on: * this * { if (x) return; * super(); * } */ Funny that this never got entered in Bugzilla before. The bug however is in the treatment of CSXreturn, mainly in scope.c. For each branch of code there are 5 cases: 1. neither constructor calls nor returns have been made. 2. at least one subbranch has returned without calling a constructor. 3. all subbranches have called a constructor. Some may have returned afterwards, but at least one has not returned yet. 4. all subbranches have exited after calling a constructor 5. some subbranches have returned after calling a constructor, the others have not yet made constructor calls. The case with the 'throw' is more difficult than the others. Ideally the first example below would be OK but the second would be an error: try { thow SomeFunkyException; } catch (SomeFunkyException) { super(); } try { thow SomeFunkyException; } catch (DifferentFunkyException) { super(); } It might be worth forbidding 'super()' inside catch clauses. I don't think it's worth the effort. But the 'return' cases should be detected.

Commit pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/ecfb19e7d602594db174d9670416916b14b38466 Fix bug 8788 The super constructor call can be prevented by mentioning "return" Fixes the flow analysis by clearly distinguishing "ALL branches have called a constructor" from "ANY branches have called a ctor". There are a large number of special cases.