C++ codegen: importcpp breaks for generic types.

[nigredo-tori]

This code:

type Vector* {.importcpp: "std::vector", header: "<vector>", nodecl.} [T] = object
proc mkVector*[T]: Vector[T] {.importcpp: "std::vector<'*0>()", header: "<vector>", constructor, nodecl.}

proc foo(): Vector[cint] =
  mkVector[cint]()

proc bar(): Vector[cstring] =
  mkVector[cstring]()

, when compiled with

nim cpp codegen_bug.nim

, produces incorrect return type in the generated C++ code (both functions are declared to return vector<int>):

typedef std::vector<int>  TY_lsra5sU08ga9bO3llT5YRoA;

/* irrelevant code here */

N_LIB_PRIVATE N_NIMCALL(TY_lsra5sU08ga9bO3llT5YRoA, foo_mtEaLGWplUQxutU9alIWbUw)(void) {
	TY_lsra5sU08ga9bO3llT5YRoA result;
	nimfr_("foo", "codegen_bug.nim");
	nimln_(5, "codegen_bug.nim");
	result = std::vector<int>();
	popFrame();
	return result;
}

N_LIB_PRIVATE N_NIMCALL(TY_lsra5sU08ga9bO3llT5YRoA, bar_mtEaLGWplUQxutU9alIWbUw_2)(void) {
	TY_lsra5sU08ga9bO3llT5YRoA result;
	nimfr_("bar", "codegen_bug.nim");
	nimln_(8, "codegen_bug.nim");
	result = std::vector<NCSTRING>();
	popFrame();
	return result;
}

, resulting in this error:

/home/dmitry/work/tmp/nimcache/codegen_bug.cpp: In function ‘TY_lsra5sU08ga9bO3llT5YRoA bar_mtEaLGWplUQxutU9alIWbUw_2()’:
/home/dmitry/work/tmp/nimcache/codegen_bug.cpp:78:33: error: no match for ‘operator=’ (operand types are ‘TY_lsra5sU08ga9bO3llT5YRoA {aka std::vector<int>}’ and ‘std::vector<char*>’)
  result = std::vector<NCSTRING>();

Nim version: devel (5d13e3f)

[cooldome]

hitted as well. Works for 0.18, definitely a regression. I suspect changes by zah for cpp codegen with static[T]

[cooldome]

Ah, before it was std::vector<NCSTRING> directly, now it is TY_sighash and hash only covers std::vector piece, NCSTRING is not part of the hash

[cooldome]

Introduced in 121b9e2

offending line: 121b9e2#diff-4ce3eb003e2427b6f7d23ad0b6231706R848

It is not clear whether it is imported type does not follow generic type conventions or it is signature computation is what is wrong

[Araq]

It is not clear whether it is imported type does not follow generic type conventions or it is signature computation is what is wrong

I don't know either. Maybe it uses the wrong signature.

[nigredo-tori]

I've poked around a bit. Vector[cstring] produces a PType structure like this:

tyGenericInst 
  tyGenericBody Vector 
    tyGenericParam T
    tyObject Vector
  tyCString cstring
  tyObject Vector

Meanwhile, in hashType:

case t.kind
...
of tyAlias, tySink, tyGenericInst, tyUserTypeClasses:
  c.hashType t.lastSon, flags
  return

That is, type parameters are not used for hash calculation.

One of these must be incorrect, but I'm not familiar enough with compiler internals to say which one.