Adds support for custom ASTs in the Nim parser (#23417)

compiler/plugins/customast.nim

@@ -0,0 +1,136 @@
+# This file exists to make it overridable via
+# patchFile("plugins", "customast.nim", "customast.nim")
+
+## This also serves as a blueprint for a possible implementation.
+
+import "$nim" / compiler / [lineinfos, idents]
+
+when defined(nimPreviewSlimSystem):
+  import std/assertions
+
+import "$nim" / compiler / nodekinds
+export nodekinds
+
+type
+  PNode* = ref TNode
+  TNode*{.final, acyclic.} = object
+    case kind*: TNodeKind
+    of nkCharLit..nkUInt64Lit:
+      intVal: BiggestInt
+    of nkFloatLit..nkFloat128Lit:
+      floatVal: BiggestFloat
+    of nkStrLit..nkTripleStrLit:
+      strVal: string
+    of nkSym:
+      discard
+    of nkIdent:
+      ident: PIdent
+    else:
+      son, next, last: PNode # linked structure instead of a `seq`
+    info*: TLineInfo
+
+const
+  bodyPos* = 6
+  paramsPos* = 3
+
+proc comment*(n: PNode): string =
+  result = ""
+
+proc `comment=`*(n: PNode, a: string) =
+  discard "XXX implement me"
+
+proc add*(father, son: PNode) =
+  assert son != nil
+  if father.son == nil:
+    father.son = son
+    father.last = son
+  else:
+    father.last.next = son
+    father.last = son
+
+template firstSon*(n: PNode): PNode = n.son
+template secondSon*(n: PNode): PNode = n.son.next
+
+proc replaceFirstSon*(n, newson: PNode) {.inline.} =
+  let old = n.son
+  n.son = newson
+  newson.next = old
+
+proc replaceSon*(n: PNode; i: int; newson: PNode) =
+  assert i > 0
+  assert newson.next == nil
+  var i = i
+  var it = n.son
+  while i > 0:
+    it = it.next
+    dec i
+  let old = it.next
+  it.next = newson
+  newson.next = old
+
+template newNodeImpl(info2) =
+  result = PNode(kind: kind, info: info2)
+
+proc newNode*(kind: TNodeKind): PNode =
+  ## new node with unknown line info, no type, and no children
+  newNodeImpl(unknownLineInfo)
+
+proc newNode*(kind: TNodeKind, info: TLineInfo): PNode =
+  ## new node with line info, no type, and no children
+  newNodeImpl(info)
+
+proc newTree*(kind: TNodeKind; info: TLineInfo; child: PNode): PNode =
+  result = newNode(kind, info)
+  result.son = child
+
+proc newAtom*(ident: PIdent, info: TLineInfo): PNode =
+  result = newNode(nkIdent)
+  result.ident = ident
+  result.info = info
+
+proc newAtom*(kind: TNodeKind, intVal: BiggestInt, info: TLineInfo): PNode =
+  result = newNode(kind, info)
+  result.intVal = intVal
+
+proc newAtom*(kind: TNodeKind, floatVal: BiggestFloat, info: TLineInfo): PNode =
+  result = newNode(kind, info)
+  result.floatVal = floatVal
+
+proc newAtom*(kind: TNodeKind; strVal: sink string; info: TLineInfo): PNode =
+  result = newNode(kind, info)
+  result.strVal = strVal
+
+proc lastSon*(n: PNode): PNode {.inline.} = n.last
+proc setLastSon*(n: PNode, s: PNode) =
+  assert s.next == nil
+  n.last = s
+  if n.son == nil: n.son = s
+
+proc newProcNode*(kind: TNodeKind, info: TLineInfo, body: PNode,
+                 params,
+                 name, pattern, genericParams,
+                 pragmas, exceptions: PNode): PNode =
+  result = newNode(kind, info)
+  result.add name
+  result.add pattern
+  result.add genericParams
+  result.add params
+  result.add pragmas
+  result.add exceptions
+  result.add body
+
+template transitionNodeKindCommon(k: TNodeKind) =
+  let obj {.inject.} = n[]
+  n[] = TNode(kind: k, info: obj.info)
+  # n.comment = obj.comment # shouldn't be needed, the address doesnt' change
+
+proc transitionSonsKind*(n: PNode, kind: range[nkComesFrom..nkTupleConstr]) =
+  transitionNodeKindCommon(kind)
+  n.son = obj.son
+
+template hasSon*(n: PNode): bool = n.son != nil
+template has2Sons*(n: PNode): bool = n.son != nil and n.son.next != nil
+
+proc isNewStyleConcept*(n: PNode): bool {.inline.} =
+  assert n.kind == nkTypeClassTy
+  result = n.firstSon.kind == nkEmpty