Bug 14093 – [REG2.065] __traits(compiles, cast(Object)(tuple)) is true even if it doesn't compile.

This code does not compile on most DMD compiler version on Linux: import std.typecons; void main() { Tuple!(int, "x", int, "y") point; static if (__traits(compiles, {auto newPoint = cast(Object)(point);})) { {auto newPoint = cast(Object)(point);} } } The compiles trait evaluates to true, even though it's impossible to cast a tuple to object. The code compiles if I run it in DPaste version "DMD 2.x Git (cfb5842b49)". It doesn't work in 2.065.0 or commit 7c769ec517e8acc086d92c9dc0d6a680b83f69f0. Since this bug seems to come and go there should probably be a unit test for it.

Introduced in https://github.com/D-Programming-Language/dmd/pull/3009 (In reply to Pierre krafft from comment #0) > The code compiles if I run it in DPaste version "DMD 2.x Git (cfb5842b49)". commit cfb5842b49 seems to be DMD 2.063.x.

The error: foo2.d(8): Error: e2ir: cannot cast __tup1850.__expand_field_0 of type int to type object.Object foo2.d(8): Error: e2ir: cannot cast __tup1850.__expand_field_1 of type int to type object.Object is coming from the glue layer. The __traits(compiles, ) does not get that far. The error check needs to be moved up into the front end to fix it.

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/1d0268e92e83ec62f0daa548e39c749902e7eb54 fix Issue 14093 - __traits(compiles, cast(Object)(tuple)) is true even if it doesn't compile. Move invalid cast check into Expression::castTo(). https://github.com/D-Programming-Language/dmd/commit/132dcccc5f29732301250ea1a1684b858cf6f555 Merge pull request #4395 from 9rnsr/fix14093 [REG2.065] Issue 14093 - __traits(compiles, cast(Object)(tuple)) is true even if it doesn't compile

Commits pushed to https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/1d0268e92e83ec62f0daa548e39c749902e7eb54 fix Issue 14093 - __traits(compiles, cast(Object)(tuple)) is true even if it doesn't compile. https://github.com/D-Programming-Language/dmd/commit/132dcccc5f29732301250ea1a1684b858cf6f555 Merge pull request #4395 from 9rnsr/fix14093

This issue is not fully solved. There is simpler example: ----------------------------------------- struct FooBar { int a; int b; } void test14093() { FooBar foo; auto obj = cast(Object)foo; //e2ir: cannot cast foo of type FooBar to type object.Object } ----------------------------------------- Moreover, I think, this issue is solved incorrectly: alias this mechanism should reject `cast(Object)(point._tupleAliasThis_)` variant and continue process the root casting "cast(Object)point" excluding alias this. And result error message should be "Error: cannot cast expression point of type Tuple!(int, "x", int, "y") to object.Object". We are interested in subtyping (alias this, or inheritance) only when it can done its work (casting, .member ...).

(In reply to Igor Stepanov from comment #6) > This issue is not fully solved. > There is simpler example: > ----------------------------------------- > struct FooBar > { > int a; > int b; > } > > void test14093() > { > FooBar foo; > auto obj = cast(Object)foo; //e2ir: cannot cast foo of type FooBar to > type object.Object > } > ----------------------------------------- Will be fixed by: https://github.com/D-Programming-Language/dmd/pull/4691 > Moreover, I think, this issue is solved incorrectly: alias this mechanism > should reject `cast(Object)(point._tupleAliasThis_)` variant and continue > process the root casting "cast(Object)point" excluding alias this. > And result error message should be > "Error: cannot cast expression point of type Tuple!(int, "x", int, "y") to > object.Object". > We are interested in subtyping (alias this, or inheritance) only when it can > done its work (casting, .member ...). It's rather diagnostic issue. I opened a new minor issue 14632.

(In reply to Kenji Hara from comment #7) > Will be fixed by: > https://github.com/D-Programming-Language/dmd/pull/4691 It was merged: https://github.com/D-Programming-Language/dmd/commit/185779938ac17bfe412f390b4971daeb07d057bd