noTypeInfo pragma to workaround C++ Atomic [backport]

fixes nim-lang#24159, refs nim-lang#23761, refs nim-lang#15928, alternative to nim-lang#24166

compiler/ast.nim

@@ -393,6 +393,9 @@ type
     tfCompleteStruct
       # (for importc types); type is fully specified, allowing to compute
       # sizeof, alignof, offsetof at CT
+    tfNoTypeInfo
+      # do not generate typeinfo for imported struct
+      # workaround for Atomic[T] on C++
     tfExplicitCallConv
     tfIsConstructor
     tfEffectSystemWorkaround

compiler/ccgtypes.nim

@@ -1402,7 +1402,8 @@ proc genObjectInfo(m: BModule; typ, origType: PType, name: Rope; info: TLineInfo
                       typeToString(typ))
   genTypeInfoAux(m, typ, origType, name, info)
   var tmp = getNimNode(m)
-  if (not isImportedType(typ)) or tfCompleteStruct in typ.flags:
+  if (not isImportedType(typ)) or
+      {tfCompleteStruct, tfNoTypeInfo} * typ.flags == {tfCompleteStruct}:
     genObjectFields(m, typ, origType, typ.n, tmp, info)
   m.s[cfsTypeInit3].addf("$1.node = &$2;$n", [tiNameForHcr(m, name), tmp])
   var t = typ.baseClass

compiler/condsyms.nim

@@ -169,3 +169,4 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimHasGenericsOpenSym2")
   defineSymbol("nimHasGenericsOpenSym3")
   defineSymbol("nimHasJsNoLambdaLifting")
+  defineSymbol("nimHasNoTypeInfoPragma")

compiler/pragmas.nim

@@ -73,7 +73,7 @@ const
     wGcSafe, wCodegenDecl, wNoInit, wCompileTime}
   typePragmas* = declPragmas + {wMagic, wAcyclic,
     wPure, wHeader, wCompilerProc, wCore, wFinal, wSize, wShallow,
-    wIncompleteStruct, wCompleteStruct, wByCopy, wByRef,
+    wIncompleteStruct, wCompleteStruct, wNoTypeInfo, wByCopy, wByRef,
     wInheritable, wGensym, wInject, wRequiresInit, wUnchecked, wUnion, wPacked,
     wCppNonPod, wBorrow, wGcSafe, wPartial, wExplain, wPackage, wCodegenDecl,
     wSendable, wNoInit}
@@ -1216,6 +1216,10 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
         noVal(c, it)
         if sym.typ == nil: invalidPragma(c, it)
         else: incl(sym.typ.flags, tfCompleteStruct)
+      of wNoTypeInfo:
+        noVal(c, it)
+        if sym.typ == nil or sfImportc notin sym.flags: invalidPragma(c, it)
+        else: incl(sym.typ.flags, tfNoTypeInfo)
       of wUnchecked:
         noVal(c, it)
         if sym.typ == nil or sym.typ.kind notin {tyArray, tyUncheckedArray}:

compiler/wordrecg.nim

@@ -46,7 +46,8 @@ type
     wImportc = "importc", wImportJs = "importjs", wExportc = "exportc", wExportCpp = "exportcpp",
     wExportNims = "exportnims",
     wIncompleteStruct = "incompleteStruct", # deprecated
-    wCompleteStruct = "completeStruct", wRequiresInit = "requiresInit", wAlign = "align",
+    wCompleteStruct = "completeStruct", wNoTypeInfo = "notypeinfo",
+    wRequiresInit = "requiresInit", wAlign = "align",
     wNodecl = "nodecl", wPure = "pure", wSideEffect = "sideEffect", wHeader = "header",
     wNoSideEffect = "noSideEffect", wGcSafe = "gcsafe", wNoreturn = "noreturn",
     wNosinks = "nosinks", wLib = "lib", wDynlib = "dynlib",

lib/pure/concurrency/atomics.nim

@@ -88,8 +88,11 @@ when defined(cpp) or defined(nimdoc):
         ## Also guarantees that all threads observe the same total ordering
         ## with other moSequentiallyConsistent operations.
 
+  when not defined(nimHasNoTypeInfoPragma):
+    {.pragma: noTypeInfo.}
+
   type
-    Atomic*[T] {.importcpp: "std::atomic", completeStruct.} = object
+    Atomic*[T] {.importcpp: "std::atomic", completeStruct, noTypeInfo.} = object
       ## An atomic object with underlying type `T`.
       raw: T
 

tests/ccgbugs/tatomictypeinfo.nim

@@ -0,0 +1,14 @@
+discard """
+  matrix: "--mm:refc; --mm:orc"
+  targets: "c cpp"
+"""
+
+# issue #24159 
+
+import std/atomics
+
+type N = object
+  u: ptr Atomic[int]
+proc w(args: N) = discard
+var e: Thread[N]
+createThread(e, w, default(N))

tests/ccgbugs/tcgbug.nim

@@ -4,6 +4,7 @@ success
 M1 M2
 ok
 '''
+targets: "c cpp"
 matrix: "--mm:refc;--mm:orc"
 """