fix Issue 20053 - add mixin types

[WalterBright]

Currently D has these mixins:

1. declaration
2. statement
3. expression

But lacks types. This adds mixin types. I.e. adding:

 MixinType:
    mixin ( ArgumentList)

to https://dlang.org/spec/declaration.html#BasicType

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20053	enhancement	add mixin types

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#10215"

[WalterBright]

@TurkeyMan FYI

[thewilsonator]

home/circleci/dmd/src/dmd/typesem.d(1893): Error: template instance Parser!ASTCodegen template Parser is not defined

[TurkeyMan]

Thank you so much. This is really good.

[WalterBright]

Yah, it was a rather glaring gap in the mixin capability.

[WalterBright]

I'll try to get it through the test suite tomorrow.

[Geod24]

Please add the following to a fail_compilation test:

struct Foo {
    alias T = mixin("T2");
}
alias T1 = mixin("Foo.T");
alias T2 = mixin("T1");
void func (T2 p) {}

Or any similar test with circular reference

[TurkeyMan]

@Geod24 Nice thinking :)

[WalterBright]

Spec: dlang/dlang.org#2684

[andralex]

I'm confused as to why this idiom was used here. It's just a more complicated way of saying... this:

override Type syntaxCopy()
{
    Expressions* a = null;
    if (exps)
    {
        a = new Expressions(exps.dim);
        foreach (i, e; *exps)
        {
            (*a)[i] = e ? e.syntaxCopy() : null;
        }
    }
    return new TypeMixin(a);
}

[WalterBright]

Because arraySyntaxCopy is used all over dmd, but is not available in astbase.d

[andralex]

superfluous parens

[Geod24]

Please also add a test for multiple arguments to mixin (e.g. mixin("a", ".", "b");)

[Geod24]

Unrelated

[Geod24]

Would have been better if this refactoring was in another PR

[Geod24]

Suggested change

	error("found `%s` when expecting `%s` following %s", token.toChars(), Token.toChars(TOK.leftParentheses), "`mixin`".ptr);
	error("found `%s` when expecting `%s` following `mixin`", token.toChars(), Token.toChars(TOK.leftParentheses));

[ghost]

This has been merged without

• changelog entry
• h file counterpart
• dlang.org PR for this.

Same standards for everyone please.

[WalterBright]

h file counterpart

Don't need it.

dlang.org PR for this.

#10215 (comment)

[WalterBright]

Please also add a test for multiple arguments to mixin (e.g. mixin("a", ".", "b");)

Not necessary due to common handling with other mixins. It's only necessary to test what is different.

[ghost]

changelog PR and we're good. Something inside this folder

[Geod24]

Not necessary due to common handling with other mixins. It's only necessary to test what is different.

This line is not shared, and what I wanted to have covered by tests.

[WalterBright]

That line looks green to me, and parseArguments() is called in 13 other places in parse.d.