cpp code gen bug in nim-glm

[dom96]

https://github.com/stavenko/nim-glm/blob/master/tests/quaternion.nim

nim cpp tests/quaternion.nim

CC: glm_mat
Error: execution of an external compiler program 'clang++ -c  -w  -I/Users/dom/projects/nim/lib -o /Users/dom/other_projects/nim-glm/tests/nimcache/glm_vec.o /Users/dom/other_projects/nim-glm/tests/nimcache/glm_vec.cpp' failed with exit code: 1

/Users/dom/other_projects/nim-glm/tests/nimcache/glm_vec.cpp:399:13: error: declaration of reference variable 'c' requires an initializer
                NIM_CHAR& c;
                          ^
/Users/dom/other_projects/nim-glm/tests/nimcache/glm_vec.cpp:400:7: error: C-style cast from rvalue to reference type 'NIM_CHAR &' (aka 'char &')
                c = (NIM_CHAR&)0;
                    ^~~~~~~~~~~~
2 errors generated.

[mratsim]

Same issue in Arraymancer mratsim/Arraymancer#91.

In Arraymancer, the codegen issue was introduced by replacing higher-order functions that accepts closures by templates that uses {.inject.}

Edit:

N_NIMCALL(void, slicerMut_5HNBiHajzTdmOUheqCgr2A)(tyObject_Tensor_8gG034a4DEBvD9ctN8nyxaw& t, tyObject_SteppedSlice_rJTlbLcKC9bpAJbFSrlwOrQ* slices, NI slicesLen_0, NI val$
        tyObject_Tensor_8gG034a4DEBvD9ctN8nyxaw sliced;
        tyObject_Tensor_8gG034a4DEBvD9ctN8nyxaw T1_;
        memset((void*)(&sliced), 0, sizeof(sliced));
        memset((void*)(&T1_), 0, sizeof(T1_));
        unsafeSlicer_SRZrYFq46KhcUYobS9bdI9cg_2((&t), slices, slicesLen_0, (&T1_));
        sliced.shape = T1_.shape;
        sliced.strides = T1_.strides;
        sliced.offset = T1_.offset;
        sliced.data = T1_.data;
        {
                NI& old_val;        // <------- here, needs initializer
                old_val = (NI&)0;  // <------- here, needs initializer
                NI* data = dataArray_v3eUw6FwA4Vs9cV5O3TkzvQtest_init((&sliced));
                {
                        if (!is_C_contiguous_dDfDc3pbZUoFoNv6AVz18Atest_init((&sliced))) goto LA5_;
{                       {
                                NI i;
                                NI colontmp_;
                                NI T8_;
                                ...

[mratsim]

Reproduced with a small test case

import sequtils

import future


type CustomSeq[T] = object
  data: seq[T]


iterator mitems[T](cs: var CustomSeq[T]): var T {.inline,noSideEffect.} =
  for val in cs.data.mitems:
    yield val

template map[T](cs: CustomSeq[T], op:untyped): untyped =
  var dest = cs

  for x {.inject.} in dest.mitems:
    x = op
  dest

let a = CustomSeq[int](data: toSeq(1..10))

let b = a.map(x * 2)

echo b

Error:

Error: execution of an external compiler program 'clang++ -c  -w  -I/Users/tesuji/.choosenim/toolchains/nim-0.17.2/lib -o ./nimcache/arraymancer_issue_6455.o ./nimcache/arraymancer_issue_6455.cpp' failed with exit code: 1

./nimcache/arraymancer_issue_6455.cpp:260:5: error: declaration of reference variable 'x_AFjtzFoe8mPqwuVFjBw4hg_2' requires an initializer
NI& x_AFjtzFoe8mPqwuVFjBw4hg_2;
    ^~~~~~~~~~~~~~~~~~~~~~~~~~
./nimcache/arraymancer_issue_6455.cpp:538:8: error: declaration of reference variable 'val' requires an initializer
                        NI& val;
                            ^~~
./nimcache/arraymancer_issue_6455.cpp:540:10: error: C-style cast from rvalue to reference type 'NI &' (aka 'long long &')
                        val = (NI&)0;
                              ^~~~~~
3 errors generated.

There is no issue with the C backend

[mratsim]

Probably duplicate of #4910 and #4048 "mitems doesn't work with C++"

[krux02]

Just tested it. It works now.