fixes #16069; [backport:1.2] [backport:1.4] (#16115)

* fixes #16069; refs https://github.com/nim-lang/RFCs/issues/257 [backport:1.2] [backport:1.4]

* make tests green again

compiler/ast.nim

@@ -1122,7 +1122,7 @@ proc safeLen*(n: PNode): int {.inline.} =
 
 proc safeArrLen*(n: PNode): int {.inline.} =
   ## works for array-like objects (strings passed as openArray in VM).
-  if n.kind in {nkStrLit..nkTripleStrLit}:result = n.strVal.len
+  if n.kind in {nkStrLit..nkTripleStrLit}: result = n.strVal.len
   elif n.kind in {nkNone..nkFloat128Lit}: result = 0
   else: result = n.len
 

compiler/ccgexprs.nim

@@ -881,6 +881,7 @@ proc genFieldCheck(p: BProc, e: PNode, obj: Rope, field: PSym) =
               [rdLoc(test), strLit, raiseInstr(p)])
 
 proc genCheckedRecordField(p: BProc, e: PNode, d: var TLoc) =
+  assert e[0].kind == nkDotExpr
   if optFieldCheck in p.options:
     var a: TLoc
     genRecordFieldAux(p, e[0], d, a)

compiler/semfold.nim

@@ -685,6 +685,7 @@ proc getConstExpr(m: PSym, n: PNode; idgen: IdGenerator; g: ModuleGraph): PNode
   of nkBracketExpr: result = foldArrayAccess(m, n, idgen, g)
   of nkDotExpr: result = foldFieldAccess(m, n, idgen, g)
   of nkCheckedFieldExpr:
+    assert n[0].kind == nkDotExpr
     result = foldFieldAccess(m, n[0], idgen, g)
   of nkStmtListExpr:
     var i = 0

compiler/transf.nim

@@ -1002,6 +1002,11 @@ proc transform(c: PTransf, n: PNode): PNode =
     return n
   of nkExceptBranch:
     result = transformExceptBranch(c, n)
+  of nkCheckedFieldExpr:
+    result = transformSons(c, n)
+    if result[0].kind != nkDotExpr:
+      # simplfied beyond a dot expression --> simplify further.
+      result = result[0]
   else:
     result = transformSons(c, n)
   when false:

compiler/trees.nim

@@ -211,6 +211,6 @@ proc stupidStmtListExpr*(n: PNode): bool =
 proc dontInlineConstant*(orig, cnst: PNode): bool {.inline.} =
   # symbols that expand to a complex constant (array, etc.) should not be
   # inlined, unless it's the empty array:
-  result = orig.kind == nkSym and
+  result = orig.kind != cnst.kind and
            cnst.kind in {nkCurly, nkPar, nkTupleConstr, nkBracket, nkObjConstr} and
            cnst.len > ord(cnst.kind == nkObjConstr)