Fix Issue 19774 - wrong code caused by opIndex

[RazvanN7]

C bar()
{
    return C(42);
}

C foo()
{
    return bar()[1];
}

struct C
{
    int x;

    ~this()
    {
        x = 0;
    }

    C opIndex(int a)
    {
        return this;
    }
}

void main()
{
    auto c = foo();
    assert(c.x == 42); /* fails; should pass */
}

return bar()[1] is rewritten to :

C __dop3 = bar();
return __dop3.opIndex(1)

Which looks correct, but the problem is that C __dop3 is generated with a lifetime that lasts until the end of the expression. As a consequence the destructor is called before the return statement. In order to fix this I rewrote the CompoundStatement that the compiler generated to a simple return statement that has a Comma expression : return (C __dop3 = bar(); __dop3.opIndex(1));

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19774	regression	wrong code caused by opIndex

⚠️⚠️⚠️ Warnings ⚠️⚠️⚠️

• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

To target stable perform these two steps:

1. Rebase your branch to upstream/stable:

git rebase --onto upstream/stable upstream/master

2. Change the base branch of your PR to stable

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#9696"

[thewilsonator]

Stable.

[JinShil]

Using the result of a comma expression has been deprecated. I don't know if that negatively affects this technique or not.

[Geod24]

Using the result of a comma expression has been deprecated. I don't know if that negatively affects this technique or not.

It does not. Internally, coma expressions are used all over the place.

[RazvanN7]

Stable.

I wanted to make sure that the failures are not due to stable missing any patches. Once I fix the issue properly, I will rebase on top of stable

[thewilsonator]

OK. Ping me when this is GTG.

[RazvanN7]

@thewilsonator

E: Some index files failed to download. They have been ignored, or old ones used instead.

on stable

[jacob-carlborg]

@RazvanN7 rebasing the branch might fix the CircleCI issue.

[RazvanN7]

@jacob-carlborg I already rebased on top of stable.

[RazvanN7]

@thewilsonator Good to go. CircleCi failure unrelated.

[jacob-carlborg]

CircleCI is using Debian Jessie, which I think is not supported anymore.

[wilzbach]

Yup -> https://circleci.com/gh/dlang/dmd/tree/stable
One just needs to update to upstream/stable.

[jacob-carlborg]

One just needs to update to upstream/stable.

#9696 (comment)

[wilzbach]

One just needs to update to upstream/stable.

#9696 (comment)

Maybe @RazvanN7 didn't update his local upstream branch in a while?
Anyhow, thanks for fixing!

[9il]

@RazvanN7 Did it fix also the same bug for opDollar?

[WalterBright]

@RazvanN7 Thank for the most clear explanation!

[RazvanN7]

@9il No, but I submitted another PR for that [1]

[1] #9725

[RazvanN7]

@WalterBright Thanks!