Bogus recursive template expansion via getSymbolsByUDA

[dlangBugzillaToGithub]

Abscissa (@Abscissa) reported this on 2018-07-22T06:51:46Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19105

CC List

• ZombineDev
• Simen Kjaeraas
• JR

Description

---------------------------------------------
module junk;

import std.traits;

struct A(Args...) {}
struct B {}
alias C = A!( getSymbolsByUDA!(junk, B) );
---------------------------------------------

$ dmd junk.d
junk.d(7): Error: template instance `A!(getSymbolsByUDA!(junk, B))` recursive template expansion
junk.d(7): Error: alias `junk.C` recursive alias declaration

[dlangBugzillaToGithub]

dlang-bot commented on 2019-07-04T13:10:11Z

@RazvanN7 created dlang/phobos pull request #7100 "Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA" fixing this issue:

- Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA

https://github.com/dlang/phobos/pull/7100

[dlangBugzillaToGithub]

dlang-bot commented on 2019-07-10T09:57:44Z

dlang/phobos pull request #7100 "Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA" was merged into master:

- 86733d5a4a5379219f04524bead35eff33c6a1a7 by RazvanN7:
  Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA

https://github.com/dlang/phobos/pull/7100

[dlangBugzillaToGithub]

simen.kjaras commented on 2019-07-18T13:21:11Z

The "fix" in PR 7100 does nothing to fix the actual issue here - it only prohibits valid use cases, and should very clearly be reverted. See issue 20054.

This issue is a DMD issue, and no amount of Phobos fiddling is gonna fix it. Here's a reduced example:

template test(alias T) {
    alias i = T.C;
    alias test = int;
}

struct A(Args...) {}

struct S1 {
    // No error
    alias dummy = test!S1;
    alias C = A!(test!S1);
}
struct S2 {
    // Recursive template expansion
    alias C = A!(test!S2);
}

As we can see, we're not using the result of T.C, and the simple use of a dummy alias prevents the recursive expansion. Clearly, something is wrong in the compiler for this behavior to happen.

[dlangBugzillaToGithub]

dlang-bot commented on 2019-08-28T12:02:39Z

@Biotronic created dlang/phobos pull request #7158 "Revert "Fix Issue 19105 - Bogus recursive template expansion via getS…" fixing this issue:

- Revert "Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA"
  
  This reverts commit 86733d5a4a5379219f04524bead35eff33c6a1a7.

https://github.com/dlang/phobos/pull/7158

[dlangBugzillaToGithub]

dlang-bot commented on 2019-12-01T23:40:16Z

dlang/phobos pull request #7158 "Revert "Fix Issue 19105 - Bogus recursive template expansion via getS…" was merged into stable:

- f286ee1b2fc65107bd164c0a5b90b1d506f576ab by Simen Kjærås:
  Revert "Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA"
  
  This reverts commit 86733d5a4a5379219f04524bead35eff33c6a1a7.

https://github.com/dlang/phobos/pull/7158

[dlangBugzillaToGithub]

petar.p.kirov commented on 2019-12-02T11:44:42Z

Reopening as per https://issues.dlang.org/show_bug.cgi?id=19105#c3.

[dlangBugzillaToGithub]

dlang-bot commented on 2019-12-07T15:26:45Z

@PetarKirov created dlang/phobos pull request #7309 "Merge stable" fixing this issue:

- Revert "Fix Issue 19105 - Bogus recursive template expansion via getSymbolsByUDA"
  
  This reverts commit 86733d5a4a5379219f04524bead35eff33c6a1a7.

- Merge pull request #7158 from Biotronic/revert-7100
  
  Revert "Fix Issue 19105 - Bogus recursive template expansion via getS…

https://github.com/dlang/phobos/pull/7309