add default field support for object in ARC/ORC (#20480)

* fresh start

* add cpp target

* add result support

* add nimPreviewRangeDefault

* reduce

* use orc

* refactor common parts

* add tuple support

* add testcase for tuple

* cleanup; fixes nimsuggest tests

* there is something wrong with cpp

* remove

* add support for seqs

* fixes style

* addd initial distinct support

* remove links

* typo

* fixes tuple defaults

* add rangedefault

* add cpp support

* fixes one more bugs

* add more hasDefaults

* fixes ordinal types

* add testcase for #16744

* add testcase for #3608

* fixes docgen

* small fix

* recursive

* fixes

* cleanup and remove tuple support

* fixes nimsuggest

* fixes generics procs

* refactor

* increases timeout

* refactor hasDefault

* zero default; disable i386

* add tuples back

* fixes bugs

* fixes tuple

* add more tests

* fix one more bug regarding tuples

* more tests and cleanup

* remove messy distinct types which must be initialized by original types

* add tests

* fixes zero default

* fixes grammar

* fixes tests

* fixes tests

* fixes tests

* fixes comments

* fixes and add testcase

* undo default values for results

Co-authored-by: flywind <43030857+xflywind@users.noreply.github.com>

compiler/sem.nim

@@ -538,6 +538,123 @@ proc setGenericParamsMisc(c: PContext; n: PNode) =
   else:
     n[miscPos][1] = orig
 
+proc caseBranchMatchesExpr(branch, matched: PNode): bool =
+  for i in 0 ..< branch.len-1:
+    if branch[i].kind == nkRange:
+      if overlap(branch[i], matched): return true
+    elif exprStructuralEquivalent(branch[i], matched):
+      return true
+
+proc pickCaseBranchIndex(caseExpr, matched: PNode): int =
+  let endsWithElse = caseExpr[^1].kind == nkElse
+  for i in 1..<caseExpr.len - endsWithElse.int:
+    if caseExpr[i].caseBranchMatchesExpr(matched):
+      return i
+  if endsWithElse:
+    return caseExpr.len - 1
+
+proc defaultFieldsForTheUninitialized(c: PContext, recNode: PNode): seq[PNode]
+proc defaultNodeField(c: PContext, a: PNode): PNode
+proc defaultNodeField(c: PContext, a: PNode, aTyp: PType): PNode
+
+const defaultFieldsSkipTypes = {tyGenericInst, tyAlias, tySink}
+
+proc defaultFieldsForTuple(c: PContext, recNode: PNode, hasDefault: var bool): seq[PNode] =
+  case recNode.kind
+  of nkRecList:
+    for field in recNode:
+      result.add defaultFieldsForTuple(c, field, hasDefault)
+  of nkSym:
+    let field = recNode.sym
+    let recType = recNode.typ.skipTypes(defaultFieldsSkipTypes)
+    if field.ast != nil: #Try to use default value
+      hasDefault = true
+      result.add newTree(nkExprColonExpr, recNode, field.ast)
+    else:
+      if recType.kind in {tyObject, tyArray, tyTuple}:
+        let asgnExpr = defaultNodeField(c, recNode, recNode.typ)
+        if asgnExpr != nil:
+          hasDefault = true
+          asgnExpr.flags.incl nfUseDefaultField
+          result.add newTree(nkExprColonExpr, recNode, asgnExpr)
+          return
+
+      let asgnType = newType(tyTypeDesc, nextTypeId(c.idgen), recType.owner)
+      rawAddSon(asgnType, recType)
+      let asgnExpr = newTree(nkCall,
+                      newSymNode(getSysMagic(c.graph, recNode.info, "zeroDefault", mZeroDefault)),
+                      newNodeIT(nkType, recNode.info, asgnType)
+                    )
+      asgnExpr.flags.incl nfUseDefaultField
+      asgnExpr.typ = recType
+      result.add newTree(nkExprColonExpr, recNode, asgnExpr)
+  else:
+    doAssert false
+
+proc defaultFieldsForTheUninitialized(c: PContext, recNode: PNode): seq[PNode] =
+  case recNode.kind
+  of nkRecList:
+    for field in recNode:
+      result.add defaultFieldsForTheUninitialized(c, field)
+  of nkRecCase:
+    let discriminator = recNode[0]
+    var selectedBranch: int
+    let defaultValue = discriminator.sym.ast
+    if defaultValue == nil:
+      # None of the branches were explicitly selected by the user and no value
+      # was given to the discrimator. We can assume that it will be initialized
+      # to zero and this will select a particular branch as a result:
+      selectedBranch = recNode.pickCaseBranchIndex newIntNode(nkIntLit#[c.graph]#, 0)
+    else: # Try to use default value
+      selectedBranch = recNode.pickCaseBranchIndex defaultValue
+      result.add newTree(nkExprColonExpr, discriminator, defaultValue)
+    result.add defaultFieldsForTheUninitialized(c, recNode[selectedBranch][^1])
+  of nkSym:
+    let field = recNode.sym
+    let recType = recNode.typ.skipTypes(defaultFieldsSkipTypes)
+    if field.ast != nil: #Try to use default value
+      result.add newTree(nkExprColonExpr, recNode, field.ast)
+    elif recType.kind in {tyObject, tyArray, tyTuple}:
+      let asgnExpr = defaultNodeField(c, recNode, recNode.typ)
+      if asgnExpr != nil:
+        asgnExpr.flags.incl nfUseDefaultField
+        result.add newTree(nkExprColonExpr, recNode, asgnExpr)
+  else:
+    doAssert false
+
+proc defaultNodeField(c: PContext, a: PNode, aTyp: PType): PNode =
+  let aTypSkip = aTyp.skipTypes(defaultFieldsSkipTypes)
+  if aTypSkip.kind == tyObject:
+    let child = defaultFieldsForTheUninitialized(c, aTyp.skipTypes(defaultFieldsSkipTypes).n)
+    if child.len > 0:
+      var asgnExpr = newTree(nkObjConstr, newNodeIT(nkType, a.info, aTyp))
+      asgnExpr.typ = aTyp
+      asgnExpr.sons.add child
+      result = semExpr(c, asgnExpr)
+  elif aTypSkip.kind == tyArray:
+    let child = defaultNodeField(c, a, aTypSkip[1])
+
+    if child != nil:
+      let node = newNode(nkIntLit)
+      node.intVal = toInt64(lengthOrd(c.graph.config, aTypSkip))
+      result = semExpr(c, newTree(nkCall, newSymNode(getSysSym(c.graph, a.info, "arrayWith"), a.info),
+              semExprWithType(c, child),
+              node
+                ))
+      result.typ = aTyp
+  elif aTypSkip.kind == tyTuple:
+    var hasDefault = false
+    if aTypSkip.n != nil:
+      let children = defaultFieldsForTuple(c, aTypSkip.n, hasDefault)
+      if hasDefault and children.len > 0:
+        result = newNodeI(nkTupleConstr, a.info)
+        result.typ = aTyp
+        result.sons.add children
+        result = semExpr(c, result)
+
+proc defaultNodeField(c: PContext, a: PNode): PNode =
+  result = defaultNodeField(c, a, a.typ)
+
 include semtempl, semgnrc, semstmts, semexprs
 
 proc addCodeForGenerics(c: PContext, n: PNode) =