deprecate do: meaning do (): + misc cleanup (#20927)

* test disable do: block lambda lifting

* fix last test [skip ci]

* deprecate `do:` meaning `do ():` + misc cleanup

closes https://github.com/nim-lang/RFCs/issues/486

* oops

* fix

* no idea what could be causing nimsuggest failure other than this

* ensure ci works

compiler/lineinfos.nim

@@ -83,8 +83,9 @@ type
     warnPtrToCstringConv = "PtrToCstringConv",
     warnEffect = "Effect",
     warnCastSizes = "CastSizes"
-    warnTemplateRedefinition = "TemplateRedefinition",
+    warnImplicitTemplateRedefinition = "ImplicitTemplateRedefinition",
     warnUnnamedBreak = "UnnamedBreak",
+    warnStmtListLambda = "StmtListLambda",
     warnUser = "User",
     # hints
     hintSuccess = "Success", hintSuccessX = "SuccessX",
@@ -181,8 +182,9 @@ const
     warnPtrToCstringConv: "unsafe conversion to 'cstring' from '$1'; this will become a compile time error in the future",
     warnEffect: "$1",
     warnCastSizes: "$1",
-    warnTemplateRedefinition: "template '$1' is implicitly redefined, consider adding an explicit .redefine pragma",
+    warnImplicitTemplateRedefinition: "template '$1' is implicitly redefined; this is deprecated, add an explicit .redefine pragma",
     warnUnnamedBreak: "Using an unnamed break in a block is deprecated; Use a named block with a named break instead",
+    warnStmtListLambda: "statement list expression assumed to be anonymous proc; this is deprecated, use `do (): ...` or `proc () = ...` instead",
     warnUser: "$1",
     hintSuccess: "operation successful: $#",
     # keep in sync with `testament.isSuccess`

compiler/semexprs.nim

@@ -1266,15 +1266,7 @@ proc semSym(c: PContext, n: PNode, sym: PSym, flags: TExprFlags): PNode =
         result = newSymNode(s, n.info)
     else:
       result = newSymNode(s, n.info)
-  of skMacro:
-    if efNoEvaluateGeneric in flags and s.ast[genericParamsPos].len > 0 or
-       (n.kind notin nkCallKinds and s.requiredParams > 0):
-      markUsed(c, n.info, s)
-      onUse(n.info, s)
-      result = symChoice(c, n, s, scClosed)
-    else:
-      result = semMacroExpr(c, n, n, s, flags)
-  of skTemplate:
+  of skMacro, skTemplate:
     if efNoEvaluateGeneric in flags and s.ast[genericParamsPos].len > 0 or
        (n.kind notin nkCallKinds and s.requiredParams > 0) or
        sfCustomPragma in sym.flags:
@@ -1283,7 +1275,10 @@ proc semSym(c: PContext, n: PNode, sym: PSym, flags: TExprFlags): PNode =
       onUse(info, s)
       result = symChoice(c, n, s, scClosed)
     else:
-      result = semTemplateExpr(c, n, s, flags)
+      case s.kind
+      of skMacro: result = semMacroExpr(c, n, n, s, flags)
+      of skTemplate: result = semTemplateExpr(c, n, s, flags)
+      else: discard # unreachable
   of skParam:
     markUsed(c, n.info, s)
     onUse(n.info, s)

compiler/semstmts.nim

@@ -509,13 +509,6 @@ proc semVarMacroPragma(c: PContext, a: PNode, n: PNode): PNode =
       let it = pragmas[i]
       let key = if it.kind in nkPragmaCallKinds and it.len >= 1: it[0] else: it
 
-      when false:
-        let lhs = b[0]
-        let clash = strTableGet(c.currentScope.symbols, lhs.ident)
-        if clash != nil:
-          # refs https://github.com/nim-lang/Nim/issues/8275
-          wrongRedefinition(c, lhs.info, lhs.ident.s, clash.info)
-
       if isPossibleMacroPragma(c, it, key):
         # we transform ``var p {.m, rest.}`` into ``m(do: var p {.rest.})`` and
         # let the semantic checker deal with it:
@@ -562,27 +555,6 @@ proc semVarMacroPragma(c: PContext, a: PNode, n: PNode): PNode =
 
         doAssert result != nil
 
-        # since a macro pragma can set pragmas, we process these here again.
-        # This is required for SqueakNim-like export pragmas.
-        if false and result.kind in {nkVarSection, nkLetSection, nkConstSection}:
-          var validPragmas: TSpecialWords
-          case result.kind
-          of nkVarSection:
-            validPragmas = varPragmas
-          of nkLetSection:
-            validPragmas = letPragmas
-          of nkConstSection:
-            validPragmas = constPragmas
-          else:
-            # unreachable
-            discard
-          for defs in result:
-            for i in 0 ..< defs.len - 2:
-              let ex = defs[i]
-              if ex.kind == nkPragmaExpr and
-                  ex[namePos].kind == nkSym and
-                  ex[pragmaPos].kind != nkEmpty:
-                pragma(c, defs[lhsPos][namePos].sym, defs[lhsPos][pragmaPos], validPragmas)
         return result
 
 template isLocalVarSym(n: PNode): bool =
@@ -1710,12 +1682,6 @@ proc semProcAnnotation(c: PContext, prc: PNode;
 
       doAssert result != nil
 
-      # since a proc annotation can set pragmas, we process these here again.
-      # This is required for SqueakNim-like export pragmas.
-      if false and result.kind in procDefs and result[namePos].kind == nkSym and
-          result[pragmasPos].kind != nkEmpty:
-        pragma(c, result[namePos].sym, result[pragmasPos], validPragmas)
-
       return result
 
 proc semInferredLambda(c: PContext, pt: TIdTable, n: PNode): PNode {.nosinks.} =

compiler/semtempl.nim

@@ -691,7 +691,7 @@ proc semTemplateDef(c: PContext, n: PNode): PNode =
   elif not comesFromShadowscope:
     if {sfTemplateRedefinition, sfGenSym} * s.flags == {}:
       #wrongRedefinition(c, n.info, proto.name.s, proto.info)
-      message(c.config, n.info, warnTemplateRedefinition, s.name.s)
+      message(c.config, n.info, warnImplicitTemplateRedefinition, s.name.s)
     symTabReplace(c.currentScope.symbols, proto, s)
   if n[patternPos].kind != nkEmpty:
     c.patterns.add(s)

compiler/sigmatch.nim

@@ -2189,6 +2189,8 @@ proc paramTypesMatchAux(m: var TCandidate, f, a: PType,
       return arg
     elif a.kind == tyVoid and f.matchesVoidProc and argOrig.kind == nkStmtList:
       # lift do blocks without params to lambdas
+      # now deprecated
+      message(c.config, argOrig.info, warnStmtListLambda)
       let p = c.graph
       let lifted = c.semExpr(c, newProcNode(nkDo, argOrig.info, body = argOrig,
           params = nkFormalParams.newTree(p.emptyNode), name = p.emptyNode, pattern = p.emptyNode,