Analysis error on explicit case fall-through

[dlangBugzillaToGithub]

Johan Engelen (@JohanEngelen) reported this on 2016-02-27T13:10:38Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=15731

CC List

• Dennis
• RazvanN

Description

The following code compiles fine without explicit fall-through, but with -version=bad it errors.

int hexStringConstant(dchar* p)
{
    while (1)
    {
        dchar c = *p++;
        switch (c)
        {
        case ' ':
        case '\t':
        case '\v':
        case '\f':
            continue;
        case '\r':
            if (*p == '
')
                continue;
            version(bad)      /// <-- Look here
              goto case;
        case '
':
            continue;
        case 0:
        case 0x1A:
            return 111;
        case '"':
            return 222;
        default:
            break;
        }
    }
}

> dmd -c bug.d
[ no problem ]

> dmd -c bug.d -w
bug.d(18): Warning: switch case fallthrough - use 'goto case;' if intended

> dmd -c bug.d -version=bad
bug.d(1): Error: function bug.hexStringConstant no return exp; or assert(0); at end of function

[dlangBugzillaToGithub]

jbc.engelen (@JohanEngelen) commented on 2016-02-27T13:59:11Z

DMD version = 2.070.0

[dlangBugzillaToGithub]

coolfool4 commented on 2018-10-28T08:09:55Z

I can't get errors nor warnings for fallthroughs except with final switches on enums (-w or -wi don't help).

Compiler versions:
- DMD64 D Compiler v2.082.0
- nightly at https://run.dlang.io/


import std.stdio;

void main() {
    int x = 0;
    switch (x) {
        case 0:
        case 1:
            writeln("woot");
            return;
        default:
    }
}

[dlangBugzillaToGithub]

coolfool4 commented on 2018-10-28T08:25:35Z

Actually I don't get fallthrough warnings for *any* switches.

[dlangBugzillaToGithub]

coolfool4 commented on 2018-10-28T08:28:38Z

So it seems to accept *empty* cases to fall through. I guess this is intended, then?

[dlangBugzillaToGithub]

razvan.nitu1305 commented on 2022-11-03T10:09:28Z

When compiling the initial example I get:

test.d(18): Error: switch case fallthrough - use 'goto case;' if intended


This seems to have been fixed

[dlangBugzillaToGithub]

dkorpel commented on 2022-11-03T10:22:18Z

(In reply to RazvanN from comment #5)
> When compiling the initial example I get:
> 
> test.d(18): Error: switch case fallthrough - use 'goto case;' if intended
> 
> 
> This seems to have been fixed

The problem is that with -version=bad, it incorrectly raises an error about missing a return statement or assert(0). That's still the case.

Here's a reduced example:
```
// accepts valid
int a()
{
    while (1)
    {
        switch (0)
        {
            case 0: // < implicit fallthrough
            default: continue;
        }
    }
}

// rejects valid
int b()
{
    while (1)
    {
        switch (0)
        {
            case 0: goto default; // < explicit fallthrough
            default: continue;
        }
    }
}
```