Bug 5944 – Five ideas for the stacktrace

This little program: int foo(int x, int y) { return x / y; } void main() { foo(1, 0); } Produces the stack trace (dmd 2.053beta): object.Error: Integer Divide by Zero ---------------- ...\test.d(5): _Dmain ---------------- While this similar Python2 program: def foo(x, y): return x / y def main(): foo(1, 0) main() Gives the stacktrace (feel fee to ignore the first global call to main()): Traceback (most recent call last): File "...\temp.py", line 5, in <module> main() File "...\temp.py", line 4, in main foo(1, 0) File "...\temp.py", line 2, in foo return x / y ZeroDivisionError: integer division or modulo by zero [Idea1] On Python the stacktrace is reversed compared to the D one, maybe this is better. [Idea2] And as first line it prints this, that's useful for D too: Traceback (most recent call last): [Idea3] And the Python stacktrace shows the line/function where the division by zero happens too, instead of just all the frames of the functions up to the one that has called the function that has generated the division by zero. I'd like to see foo() too in the D stacktrace. ------------------------------------ This program: int foo(int x) { if (x > 0) return bar(x - 1); else return 10 / x; } int bar(int x) { if (x > 0) return foo(x - 1); else return 10 / x; } void main() { foo(10); } dmd 2.053beta (witout -g switch) gives: object.Error: Integer Divide by Zero ---------------- 40CCF4 40CB6B 402041 402021 402041 402021 402041 402021 402041 402021 402041 402021 40205A 4025FB 4021F7 411FDD ---------------- [Idea4] When the -g switch is not used I suggest to add a note about missing debug info, useful for not expert programmers/newbies: object.Error: Integer Divide by Zero ---------------- Traceback, no symbolic debug info (most recent call last): 40CCF4 40CB6B 402041 402021 402041 402021 402041 402021 402041 402021 402041 402021 40205A 4025FB 4021F7 411FDD ---------------- Instead of just: object.Error: Integer Divide by Zero ---------------- Traceback (most recent call last): 40CCF4 40CB6B 402041 402021 402041 402021 402041 402021 402041 402021 402041 402021 40205A 4025FB 4021F7 411FDD ---------------- ------------------------------------ This little program: int foo(int x) { if (x > 0) return foo(x - 1); else return 10 / x; } void main() { foo(10); } dmd 2.053beta gives just (here DMD has performed tail-call optimization, so there are no stack frames to show for the recursive calls to foo()): object.Error: Integer Divide by Zero ---------------- ... ---------------- A bigger similar example: import core.stdc.stdio: printf; nothrow pure int str2int(const char *str, in int n=0) { if (str == null || *str == '\0') { int x = 10 / cast(size_t)*str; // A bug return n; } else return str2int(str+1, n*10 + *str-'0'); } void main() { printf("%d\n", str2int("12345678".ptr)); } The asm shows that DMD performs the tail-call optimization on str2int(): _D5test37str2intFNaNbxPaxiZi comdat push EBX mov EBX,8[ESP] test EBX,EBX push ESI mov ESI,EAX push EDI je L12 cmp byte ptr [EBX],0 jne L1A L12: pop EDI mov EAX,ESI pop ESI pop EBX ret 4 L1A: lea EDX,1[EBX] movzx ECX,byte ptr [EBX] lea EDI,[ESI*4][ESI] lea EDI,-030h[EDI*2][ECX] mov ESI,EDI mov EBX,EDX test EDX,EDX je L12 cmp byte ptr [EDX],0 je L12 jmp short L1A object.Error: Integer Divide by Zero ---------------- ... ---------------- [Idea5] In this case the stacktrace may add a note: object.Error: Integer Divide by Zero ---------------- ...\test.d(4): int test.str2int(const char*, const int) [Tail-Call Optimized] ---------------- -------------------------------------- This little program just crashes at runtime (dmd 2.053beta): int foo() { return foo(); } void main() { foo(); } With DMD 2.052 it gives: object.Error: Stack Overflow ------------------------------------

KennyTM~ reminds me that the [idea 3] is bugus, because divisions by zero are not DMD exceptions. So please ignore it.

> [Idea1] On Python the stacktrace is reversed compared to the D one, maybe this is better. Definitely better, important information is easier to find in the console.

debug info is broken with dmd: eg last frame often skipped; line numbers often off by a few lines [plus or minus], debug info also gets broken with partial recompilation with ldc these problems go away

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