Fix #6415 (#7281)

* hangle static generic params when used in the importcpp pragma

* importcpp works for generic types with fields; fixes #6415

* revert a too agressive safety check that ended up breaking the tests

changelog.md

@@ -25,3 +25,8 @@
 ### Compiler changes
 
 ### Bugfixes
+
+- The `importcpp` pragma now allows importing the listed fields of generic
+  C++ types. Support for numeric parameters have also been added through
+  the use of `static[T]` types.
+  (#6415)

compiler/ccgtypes.nim

@@ -617,8 +617,10 @@ proc scanCppGenericSlot(pat: string, cursor, outIdx, outStars: var int): bool =
     return false
 
 proc resolveStarsInCppType(typ: PType, idx, stars: int): PType =
-  # XXX: we should catch this earlier and report it as a semantic error
-  if idx >= typ.len: internalError "invalid apostrophe type parameter index"
+  # Make sure the index refers to one of the generic params of the type.
+  # XXX: we should catch this earlier and report it as a semantic error.
+  if idx >= typ.len:
+    internalError "invalid apostrophe type parameter index"
 
   result = typ.sons[idx]
   for i in 1..stars:
@@ -820,6 +822,9 @@ proc getTypeDescAux(m: BModule, origTyp: PType, check: var IntSet): Rope =
             let typeInSlot = resolveStarsInCppType(origTyp, idx + 1, stars)
             if typeInSlot == nil or typeInSlot.kind == tyVoid:
               result.add(~"void")
+            elif typeInSlot.kind == tyStatic:
+              internalAssert typeInSlot.n != nil
+              result.add typeInSlot.n.renderTree
             else:
               result.add getTypeDescAux(m, typeInSlot, check)
         else:

compiler/semtypes.nim

@@ -632,16 +632,18 @@ proc semRecordNodeAux(c: PContext, n: PNode, check: var IntSet, pos: var int,
     else:
       typ = semTypeNode(c, n.sons[length-2], nil)
       propagateToOwner(rectype, typ)
-    let rec = rectype.sym
+    var fieldOwner = if c.inGenericContext > 0: c.getCurrOwner
+                     else: rectype.sym
     for i in countup(0, sonsLen(n)-3):
       var f = semIdentWithPragma(c, skField, n.sons[i], {sfExported})
       suggestSym(n.sons[i].info, f, c.graph.usageSym)
       f.typ = typ
       f.position = pos
-      if (rec != nil) and ({sfImportc, sfExportc} * rec.flags != {}) and
-          (f.loc.r == nil):
+      if fieldOwner != nil and
+         {sfImportc, sfExportc} * fieldOwner.flags != {} and
+         f.loc.r == nil:
         f.loc.r = rope(f.name.s)
-        f.flags = f.flags + ({sfImportc, sfExportc} * rec.flags)
+        f.flags = f.flags + ({sfImportc, sfExportc} * fieldOwner.flags)
       inc(pos)
       if containsOrIncl(check, f.name.id):
         localError(n.sons[i].info, errAttemptToRedefine, f.name.s)

tests/statictypes/tstaticimportcpp.nim

@@ -0,0 +1,53 @@
+discard """
+targets: "cpp"
+output: "[0, 0, 10, 0]\n5\n1.2\n15\ntest"
+"""
+
+{.emit: """
+
+template <int N, class T>
+struct GenericIntType {
+  T data[N];
+};
+
+template <class T>
+struct GenericTType {
+  T field;
+};
+
+struct SimpleStruct {
+  int field;
+};
+
+
+""" .}
+
+type
+  GenericIntType {.importcpp: "GenericIntType<'0, '1>".} [N: static[int]; T] = object
+    data: array[N, T]
+
+  GenericTType {.importcpp: "GenericTType<'0>".} [T] = object
+    field: T
+
+  GenInt4 = GenericIntType[4, int]
+
+  SimpleStruct {.importcpp: "SimpleStruct"} = object
+    field: int
+
+var
+  a = GenInt4()
+  b = SimpleStruct()
+  c = GenericTType[float]()
+  d = SimpleStruct(field: 15)
+  e = GenericTType[string](field: "test")
+
+a.data[2] = 10
+b.field = 5
+c.field = 1.2
+
+echo a.data
+echo b.field
+echo c.field
+echo d.field
+echo e.field
+