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digitalmars.D.bugs - [Issue 9514] New: "template instance … is not an alias"

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9514

           Summary: "template instance … is not an alias"
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: code klickverbot.at



PST ---
Unfortunately I don't have a reduced test case yet, but DMD from the latest
staging branch (6207580a) contains at least one regression that affects Thrift.

To reproduce, run:
git clone git://git.apache.org/thrift.git
cd thrift/lib/d/src
dmd -c -unittest thrift/internal/codegen.d

It will fail with

---
thrift/internal/codegen.d(125): Error: template instance find!("a.name == b")
find is not a template declaration, it is a alias
---

and a slew of follow-up error messages.

Note the "import std.algorithm : find" a few lines before; the issue might be
related to selective import handling.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9514


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com



22:39:30 PST ---
If you remove the ": find" it does work.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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This problem had occured by this commit:
Revision: de4f8f6bf8dc9fcc1730ea4d7f2bbd3e74880f08
Message:


Issue 5933 & 7159 & 9377 - Invoke function semantic3 correctly where it is
required.

----
Fix-up way for thrift code is:

In thrift/libe/d/src/thrift/codegen/base.d
version (unittest) {
  // Cannot make this nested in the unittest block due to a »no size yet for
  // forward reference« error.
  struct Foo { //----> Move Foo into unittest with changing to `static struct`
    string a;
    int b;
    int c;

    mixin TStructHelpers!([
      TFieldMeta("a", 1),
      TFieldMeta("b", 2, TReq.OPT_IN_REQ_OUT),
      TFieldMeta("c", 3, TReq.REQUIRED, "4")
    ]);
  }
}

----
I think this is not a compiler issue.

Before the compiler change, a member template function call had not run its
semantic3 in some case. It was wrong for auto return type inference and
attribute inference feature, but at the same time it had accidentally deferred
some forward reference error. In past std.numeric module has such a hidden
forward reference bug, and I had fixed it for compiler. 
Even worse thing, fixing such a bug is sometimes much difficult. If a template
member function is tested inside template constraint, the actual error messages
will be gagged.

Note: workaround pull for std.numeric module.
https://github.com/D-Programming-Language/phobos/pull/1096

Let's back to the Thrift code issue. This is just my prediction, the Foo
declaration contains "mixin TStructHelpers!(...)", and it may have some forward
reference error as like explained above.

David Nadlinger, You have control.

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PST ---


 Let's back to the Thrift code issue. This is just my prediction, the Foo
 declaration contains "mixin TStructHelpers!(...)", and it may have some forward
 reference error as like explained above.


Okay, the issue seems to be connected to the fact that the code contains an
import cycle between thrift.internal.codegen and thrift.codegen.base (that I
probably introduced by accident while refactoring).

You say that you think that this is not a compiler issue. Could you elaborate a
bit? Moving the struct inside the unittest block hides the problem because the
struct is no longer semantic'd. But I'm not sure what part of the code would be
illegal in the first place?

I can certainly work around the issue in the Thrift tests (although it's a bit
cumbersome, as I don't have commit access). The thing I'm worried about is
pushing out a release with a known regression/change in behavior that leads to
a completely nonsensical error message and might also occur in other code.

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14:21:01 PST ---
So far, I've reduced it to:
------------------------------

import std.typetuple : TypeTuple;

template TStructHelpers() {
    alias typeof(this) This;

    bool opEquals(This ) {
    thriftOpEqualsImpl;
    }

    bool thriftOpEqualsImpl() {
    foreach (name; FieldNames!This)
        return ;
    }
}


struct Foo {
    mixin TStructHelpers!();
}

template memberReq(T, string name, alias fieldMetaData = cast()null) {
    enum memberReq = memberReqImpl!(T, name, fieldMetaData);
}

import std.algorithm : find;

template memberReqImpl(T, string name, alias fieldMetaData) {
    enum meta = find!`a.name == b`;
}

template notIgnored(T, string name= null) {
    enum notIgnored = memberReq!(T, name) ;
}

template FieldNames(T, alias fieldMetaData = cast()null) {
    StaticFilter!(
    All!(
    PApply!(),
    PApply!(notIgnored, T)
    )) FieldNames;
}

template StaticFilter(alias pred) {
    static if (pred!()) TypeTuple!() StaticFilter;
}

template PApply()
{
    alias void PApply;
}

template PApply(alias Target, T...) {
template PApply() {
Target!(PApplyMergeArgs!(ConfinedTuple!T).Result) PApply;
}
}

template PApplyMergeArgs(alias Preset) {
alias TypeTuple!(Preset.Tuple) Result;
}

template Instantiate(alias Template, Params...) {
Template!Params Instantiate;
}

template All(T...) {
template All() {
Instantiate!(T[1 .. $])All;
}
}

template ConfinedTuple(T...) {
alias T Tuple;
}

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15:09:19 PST ---
A smaller case:
----------------
template TStructHelpers() {

    void opEquals(Foo) {
        FieldNames!();
    }
}


struct Foo {
    mixin TStructHelpers!();
}

import std.algorithm : find;

template FieldNames() {
    static if (find!`true`) int FieldNames;
}

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 A smaller case:
 ----------------
 template TStructHelpers() {
 
     void opEquals(Foo) {
         FieldNames!();
     }
 }
 
 
 struct Foo {
     mixin TStructHelpers!();
 }
 
 import std.algorithm : find;
 
 template FieldNames() {
     static if (find!`true`) int FieldNames;
 }


Hmm, maybe the root cause is the combination of selective import and unresolved

it in the table.

Technically, current "selective/renamed import" makes anonymous import
declaration and alias declaration. They have no internal relation, so forward
reference resolution is done separately. BUT, it should be together.

Yet I don't know well about the import mechanism. I need a bit more time to fix
it...

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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull, rejects-valid





 Hmm, maybe the root cause is the combination of selective import and unresolved

 it in the table.


OK, I finally agree that this is an actual compiler regression.

https://github.com/D-Programming-Language/dmd/pull/1665

Walter, thank you for your case reduction work.

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Commit pushed to staging at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/0efbffdaab79b7b099e780716aebf92a6054e26e


Issue 9514 - "template instance … is not an alias"

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12:17:26 PST ---
The bulk of the reduction was done by dustmite, an amazing tool.

The rest was done by hand.

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/4040d2578026554719eb983ba487726188b18908
fix Issue 9514 - "template instance … is not an alias"

https://github.com/D-Programming-Language/dmd/commit/03b0cad6bdfe9646f0907ca3abb8d1ac65073192


Issue 9514 - "template instance … is not an alias"

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prev sibling parent d-bugmail puremagic.com writes:
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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |verylonglogin.reg gmail.com



---
*** Issue 8907 has been marked as a duplicate of this issue. ***

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Apr 06 2013