mixin ... isn't a template error when used in new scope

[dlangBugzillaToGithub]

tetyys reported this on 2018-02-06T22:30:31Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18386

CC List

• Nick Treleaven (@ntrel)

Description

Compilation of this code:

import std.stdio;

void main() { }

class c {
        this() {
                enum string b(alias d)() {
                        return `writeln("a");`;
                }

                int a;

                {
                        mixin b!a;
                        mixin b!a;
                }
        }
}

fails with dmd v2.078.1 and error

test.d(11): Error: mixin b!a b isn't a template

However, code:


import std.stdio;

void main() { }

class c {
        this() {
                enum string b(alias d)() {
                        return `writeln("a");`;
                }

                int a;

                //{
                        mixin b!a;
                        mixin b!a;
                //}
        }
}

compiles successfully

[dlangBugzillaToGithub]

nick (@ntrel) commented on 2022-05-30T13:55:17Z

Is a function allowed to return an `enum string`? Shouldn't you use one of these:

string b(alias d)() {
    return `writeln("a");`;
}

enum string b(alias d) = `writeln("a");`;

I think this should be marked `accepts-invalid`.

[dlangBugzillaToGithub]

nick (@ntrel) commented on 2022-05-30T13:58:22Z

Also you should use a string mixin, `mixin(b!a);` - not a template mixin.

[dlangBugzillaToGithub]

nick (@ntrel) commented on 2022-06-02T15:25:54Z

I think mixing in an eponymous template should be an error as it is confusing. Reduced:

void main() {
    template b(alias d) {
        enum b = ``;
    }

    int a;

    {
        pragma(msg, is(typeof(b) == string)); // false
        mixin b!a;
        pragma(msg, is(typeof(b) == string)); // true
        mixin b!a; // error
    }
}

As before, if the {} scope block braces are removed, there's no error.