delay size pragma for generic types, use it for C++ Atomic[T]

fixes nim-lang#24159, refs nim-lang#15928 etc

compiler/ast.nim

@@ -365,6 +365,8 @@ type
     tfVarIsPtr,       # 'var' type is translated like 'ptr' even in C++ mode
     tfHasMeta,        # type contains "wildcard" sub-types such as generic params
                       # or other type classes
+                      # also used when checking pragmas of forward types
+                      # to signify that the forward type is generic
     tfHasGCedMem,     # type contains GC'ed memory
     tfPacked
     tfHasStatic
@@ -399,6 +401,9 @@ type
     tfIsOutParam
     tfSendable
     tfImplicitStatic
+    tfHasUnresolvedProperties
+      ## for types that have type properties like `size` that depend on
+      ## generic parameters
 
   TTypeFlags* = set[TTypeFlag]
 

compiler/pragmas.nim

@@ -943,16 +943,26 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
         processImportObjC(c, sym, getOptionalStr(c, it, "$1"), it.info)
       of wSize:
         if sym.typ == nil: invalidPragma(c, it)
-        var size = expectIntLit(c, it)
-        case size
-        of 1, 2, 4:
-          sym.typ.size = size
-          sym.typ.align = int16 size
-        of 8:
-          sym.typ.size = 8
-          sym.typ.align = floatInt64Align(c.config)
+        if sym.typ.kind == tyForward and tfHasMeta in sym.typ.flags:
+          # generic forward type, value possibly depends on generic types
+          # but generic type symbols aren't defined yet, so assume they are
+          # and ignore expression for now
+          sym.typ.flags.incl tfHasUnresolvedProperties
         else:
-          localError(c.config, it.info, "size may only be 1, 2, 4 or 8")
+          var size = expectIntLit(c, it)
+          if sfImportc in sym.flags:
+            # no restrictions on size for imported types
+            setImportedTypeSize(c.config, sym.typ, size)
+          else:
+            case size
+            of 1, 2, 4:
+              sym.typ.size = size
+              sym.typ.align = int16 size
+            of 8:
+              sym.typ.size = 8
+              sym.typ.align = floatInt64Align(c.config)
+            else:
+              localError(c.config, it.info, "size may only be 1, 2, 4 or 8")
       of wAlign:
         let alignment = expectIntLit(c, it)
         if isPowerOfTwo(alignment) and alignment > 0:

compiler/semstmts.nim

@@ -1445,7 +1445,12 @@ proc typeDefLeftSidePass(c: PContext, typeSection: PNode, i: int) =
     s = semIdentDef(c, name, skType)
     onDef(name.info, s)
     s.typ = newTypeS(tyForward, c)
-    s.typ.sym = s             # process pragmas:
+    let isGeneric = typeDef[1].kind != nkEmpty
+    if isGeneric:
+      # mark as tfHasMeta for pragmas to know this type is generic
+      s.typ.flags.incl tfHasMeta
+    s.typ.sym = s
+    # process pragmas:
     if name.kind == nkPragmaExpr:
       let rewritten = applyTypeSectionPragmas(c, name[1], typeDef)
       if rewritten != nil:
@@ -1458,6 +1463,9 @@ proc typeDefLeftSidePass(c: PContext, typeSection: PNode, i: int) =
         typeDefLeftSidePass(c, typeSection, i)
         return
       pragma(c, s, name[1], typePragmas)
+    if isGeneric:
+      # remove previously set tfHasMeta to mark generic parameters
+      s.typ.flags.excl tfHasMeta
     if sfForward in s.flags:
       # check if the symbol already exists:
       let pkg = c.module.owner

compiler/semtypinst.nim

@@ -12,12 +12,12 @@
 import std / tables
 
 import ast, astalgo, msgs, types, magicsys, semdata, renderer, options,
-  lineinfos, modulegraphs
+  lineinfos, modulegraphs, trees, wordrecg
 
 when defined(nimPreviewSlimSystem):
   import std/assertions
 
-const tfInstClearedFlags = {tfHasMeta, tfUnresolved}
+const tfInstClearedFlags = {tfHasMeta, tfUnresolved, tfHasUnresolvedProperties}
 
 proc checkPartialConstructedType(conf: ConfigRef; info: TLineInfo, t: PType) =
   if t.kind in {tyVar, tyLent} and t.elementType.kind in {tyVar, tyLent}:
@@ -592,6 +592,27 @@ proc propagateFieldFlags(t: PType, n: PNode) =
       propagateFieldFlags(t, son)
   else: discard
 
+proc computeUnresolvedProperties(cl: var TReplTypeVars, result, t: PType) =
+  assert t.sym != nil and t.sym.ast != nil and t.sym.ast[0].kind == nkPragmaExpr
+  let pragmas = t.sym.ast[0][1]
+  for prag in pragmas:
+    let key = whichPragma(prag)
+    case key
+    of wSize:
+      if prag.kind notin nkPragmaCallKinds or prag.len != 2:
+        localError(cl.c.config, prag.info, "expected argument for `size` pragma")
+      var e = prepareNode(cl, prag[1])
+      e = cl.c.semConstExpr(cl.c, e)
+      var val = 0
+      case e.kind
+      of nkIntLit..nkInt64Lit:
+        val = int(e.intVal)
+      else:
+        localError(cl.c.config, e.info, "integer value expected for `size`")
+      setImportedTypeSize(cl.c.config, result, val)
+    else: discard
+  result.flags.excl tfHasUnresolvedProperties
+
 proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
   template bailout =
     if (t.sym == nil) or (t.sym != nil and sfGeneratedType in t.sym.flags):
@@ -771,6 +792,8 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
         result.setIndexType result.indexType.skipTypes({tyStatic, tyDistinct})
 
       else: discard
+      if tfHasUnresolvedProperties in result.flags:
+        computeUnresolvedProperties(cl, result, t)
     else:
       # If this type doesn't refer to a generic type we may still want to run it
       # trough replaceObjBranches in order to resolve any pending nkRecWhen nodes
@@ -784,6 +807,11 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
         # Invalidate the type size as we may alter its structure
         result.size = -1
         result.n = replaceObjBranches(cl, result.n)
+      if tfHasUnresolvedProperties in result.flags:
+        # this can be reached for empty `object` generic bodies
+        result = instCopyType(cl, result)
+        result.size = -1 # needs to be recomputed
+        computeUnresolvedProperties(cl, result, t)
 
 proc initTypeVars*(p: PContext, typeMap: LayeredIdTable, info: TLineInfo;
                    owner: PSym): TReplTypeVars =

compiler/types.nim

@@ -1483,6 +1483,17 @@ proc getSize*(conf: ConfigRef; typ: PType): BiggestInt =
   computeSizeAlign(conf, typ)
   result = typ.size
 
+proc setImportedTypeSize*(conf: ConfigRef, t: PType, size: int) =
+  t.size = size
+  if tfPacked in t.flags or size <= 1:
+    t.align = 1
+  elif size <= 2:
+    t.align = 2
+  elif size <= 4:
+    t.align = 4
+  else:
+    t.align = floatInt64Align(conf)
+
 proc containsGenericTypeIter(t: PType, closure: RootRef): bool =
   case t.kind
   of tyStatic:

doc/manual.md

@@ -7720,6 +7720,8 @@ The `size pragma` allows specifying the size of the enum type.
   doAssert sizeof(EventType) == sizeof(uint32)
   ```
 
+For this purpose, the `size pragma` accepts only the values 1, 2, 4 or 8.
+
 The `size pragma` can also specify the size of an `importc` incomplete object type
 so that one can get the size of it at compile time even if it was declared without fields.
 
@@ -7732,8 +7734,6 @@ so that one can get the size of it at compile time even if it was declared witho
       echo sizeof(AtomicFlag)
   ```
 
-The `size pragma` accepts only the values 1, 2, 4 or 8.
-
 
 Align pragma
 ------------

lib/pure/concurrency/atomics.nim

@@ -89,9 +89,8 @@ when defined(cpp) or defined(nimdoc):
         ## with other moSequentiallyConsistent operations.
 
   type
-    Atomic*[T] {.importcpp: "std::atomic", completeStruct.} = object
+    Atomic*[T] {.importcpp: "std::atomic", size: sizeof(T).} = object
       ## An atomic object with underlying type `T`.
-      raw: T
 
     AtomicFlag* {.importcpp: "std::atomic_flag", size: 1.} = object
       ## An atomic boolean state.

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"
 """