fixes #24801; Invalid C codegen generated when destroying distinct seq types (#24835)

fixes #24801

Because distinct `seq` types match `proc `=destroy`*[T](x: var T)
{.inline, magic: "Destroy".}`. But the Nim compiler generates lifted seq
types for corresponding distinct types. So we skip the address for
distinct types.

Related to #22207 I had a hard time
finding the other place where generic destructors get replaced by
attachedDestructors

Author: ringabout

compiler/liftdestructors.nim

@@ -40,7 +40,7 @@ template asink*(t: PType): PSym = getAttachedOp(c.g, t, attachedSink)
 
 proc fillBody(c: var TLiftCtx; t: PType; body, x, y: PNode)
 proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
-              info: TLineInfo; idgen: IdGenerator; isDistinct = false): PSym
+              info: TLineInfo; idgen: IdGenerator): PSym
 
 proc createTypeBoundOps*(g: ModuleGraph; c: PContext; orig: PType; info: TLineInfo;
                          idgen: IdGenerator)
@@ -1063,9 +1063,7 @@ proc produceSymDistinctType(g: ModuleGraph; c: PContext; typ: PType;
   assert typ.kind == tyDistinct
   let baseType = typ.elementType
   if getAttachedOp(g, baseType, kind) == nil:
-    # TODO: fixme `isDistinct` is a fix for #23552; remove it after
-    # `-d:nimPreviewNonVarDestructor` becomes the default
-    discard produceSym(g, c, baseType, kind, info, idgen, isDistinct = true)
+    discard produceSym(g, c, baseType, kind, info, idgen)
   result = getAttachedOp(g, baseType, kind)
   setAttachedOp(g, idgen.module, typ, kind, result)
 
@@ -1104,7 +1102,7 @@ proc symDupPrototype(g: ModuleGraph; typ: PType; owner: PSym; kind: TTypeAttache
   incl result.flags, sfGeneratedOp
 
 proc symPrototype(g: ModuleGraph; typ: PType; owner: PSym; kind: TTypeAttachedOp;
-              info: TLineInfo; idgen: IdGenerator; isDiscriminant = false; isDistinct = false): PSym =
+              info: TLineInfo; idgen: IdGenerator; isDiscriminant = false): PSym =
   if kind == attachedDup:
     return symDupPrototype(g, typ, owner, kind, info, idgen)
 
@@ -1115,7 +1113,7 @@ proc symPrototype(g: ModuleGraph; typ: PType; owner: PSym; kind: TTypeAttachedOp
                    idgen, result, info)
 
   if kind == attachedDestructor and g.config.selectedGC in {gcArc, gcOrc, gcAtomicArc} and
-     ((g.config.isDefined("nimPreviewNonVarDestructor") and not isDiscriminant) or (typ.kind in {tyRef, tyString, tySequence} and not isDistinct)):
+     ((g.config.isDefined("nimPreviewNonVarDestructor") and not isDiscriminant) or (typ.kind in {tyRef, tyString, tySequence})):
     dest.typ = typ
   else:
     dest.typ = makeVarType(typ.owner, typ, idgen)
@@ -1157,13 +1155,13 @@ proc genTypeFieldCopy(c: var TLiftCtx; t: PType; body, x, y: PNode) =
   body.add newAsgnStmt(xx, yy)
 
 proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
-              info: TLineInfo; idgen: IdGenerator; isDistinct = false): PSym =
+              info: TLineInfo; idgen: IdGenerator): PSym =
   if typ.kind == tyDistinct:
     return produceSymDistinctType(g, c, typ, kind, info, idgen)
 
   result = getAttachedOp(g, typ, kind)
   if result == nil:
-    result = symPrototype(g, typ, typ.owner, kind, info, idgen, isDistinct = isDistinct)
+    result = symPrototype(g, typ, typ.owner, kind, info, idgen)
 
   var a = TLiftCtx(info: info, g: g, kind: kind, c: c, asgnForType: typ, idgen: idgen,
                    fn: result)

compiler/sempass2.nim

@@ -11,7 +11,7 @@ import
   ast, astalgo, msgs, renderer, magicsys, types, idents, trees,
   wordrecg, options, guards, lineinfos, semfold, semdata,
   modulegraphs, varpartitions, typeallowed, nilcheck, errorhandling,
-  semstrictfuncs, suggestsymdb, pushpoppragmas
+  semstrictfuncs, suggestsymdb, pushpoppragmas, lowerings
 
 import std/[tables, intsets, strutils, sequtils]
 
@@ -1081,6 +1081,13 @@ proc trackCall(tracked: PEffects; n: PNode) =
         let op = getAttachedOp(tracked.graph, t, TTypeAttachedOp(opKind))
         if op != nil:
           n[0].sym = op
+          if TTypeAttachedOp(opKind) == attachedDestructor and
+              op.typ.len == 2 and op.typ.firstParamType.kind != tyVar:
+            if n[1].kind == nkSym and n[1].sym.kind == skParam and
+                n[1].typ.kind == tyVar:
+              n[1] = genDeref(n[1])
+            else:
+              n[1] = skipAddr(n[1])
 
   if op != nil and op.kind == tyProc:
     for i in 1..<min(n.safeLen, op.signatureLen):

tests/destructor/tdistinctseq.nim

@@ -6,3 +6,26 @@ type DistinctSeq* = distinct seq[int]
 # `=destroy`(cast[ptr DistinctSeq](0)[])
 var x = @[].DistinctSeq
 `=destroy`(x)
+
+
+import std/options
+
+# bug #24801
+type
+  B[T] = object
+    case r: bool
+    of false:
+      v: ref int
+    of true:
+      x: T
+  E = distinct seq[int]
+  U = ref object of RootObj
+  G = ref object of U
+
+proc a(): E = default(E)
+method c(_: U): seq[E] {.base.} = discard
+proc p(): seq[E] = c(default(U))
+method c(_: G): seq[E] = discard E(newSeq[seq[int]](1)[0])
+method y(_: U) {.base.} =
+  let s = default(B[tuple[f: B[int], w: B[int]]])
+  discard some(s.x)