implements https://github.com/nim-lang/RFCs/issues/258 (#15503)

* implements https://github.com/nim-lang/RFCs/issues/258

* don't be too strict with custom pragma blocks

* cast pragmas: documentation

* added most missing inference query procs to effecttraits.nim

compiler/condsyms.nim

@@ -121,3 +121,5 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimHasLentIterators")
   defineSymbol("nimHasDeclaredMagic")
   defineSymbol("nimHasStacktracesModule")
+  defineSymbol("nimHasEffectTraitsModule")
+  defineSymbol("nimHasCastPragmaBlocks")

compiler/parser.nim

@@ -485,17 +485,24 @@ proc setOrTableConstr(p: var Parser): PNode =
   eat(p, tkCurlyRi) # skip '}'
 
 proc parseCast(p: var Parser): PNode =
-  #| castExpr = 'cast' '[' optInd typeDesc optPar ']' '(' optInd expr optPar ')'
+  #| castExpr = 'cast' ('[' optInd typeDesc optPar ']' '(' optInd expr optPar ')') /
+  #                    ('(' optInd exprColonEqExpr optPar ')')
   result = newNodeP(nkCast, p)
   getTok(p)
-  eat(p, tkBracketLe)
-  optInd(p, result)
-  result.add(parseTypeDesc(p))
-  optPar(p)
-  eat(p, tkBracketRi)
-  eat(p, tkParLe)
-  optInd(p, result)
-  result.add(parseExpr(p))
+  if p.tok.tokType == tkBracketLe:
+    getTok(p)
+    optInd(p, result)
+    result.add(parseTypeDesc(p))
+    optPar(p)
+    eat(p, tkBracketRi)
+    eat(p, tkParLe)
+    optInd(p, result)
+    result.add(parseExpr(p))
+  else:
+    result.add p.emptyNode
+    eat(p, tkParLe)
+    optInd(p, result)
+    result.add(exprColonEqExpr(p))
   optPar(p)
   eat(p, tkParRi)
 

compiler/pragmas.nim

@@ -771,6 +771,15 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
   if key.kind == nkBracketExpr:
     processNote(c, it)
     return
+  elif key.kind == nkCast:
+    if comesFromPush:
+      localError(c.config, n.info, "a 'cast' pragma cannot be pushed")
+    elif not isStatement:
+      localError(c.config, n.info, "'cast' pragma only allowed in a statement context")
+    case whichPragma(key[1])
+    of wRaises, wTags: pragmaRaisesOrTags(c, key[1])
+    else: discard
+    return
   elif key.kind notin nkIdentKinds:
     n[i] = semCustomPragma(c, it)
     return

compiler/renderer.nim

@@ -1057,9 +1057,10 @@ proc gsub(g: var TSrcGen, n: PNode, c: TContext) =
       put(g, tkSymbol, "(wrong conv)")
   of nkCast:
     put(g, tkCast, "cast")
-    put(g, tkBracketLe, "[")
-    gsub(g, n, 0)
-    put(g, tkBracketRi, "]")
+    if n.len > 0 and n[0].kind != nkEmpty:
+      put(g, tkBracketLe, "[")
+      gsub(g, n, 0)
+      put(g, tkBracketRi, "]")
     put(g, tkParLe, "(")
     gsub(g, n, 1)
     put(g, tkParRi, ")")

compiler/sempass2.nim

@@ -325,7 +325,7 @@ proc createTag(g: ModuleGraph; n: PNode): PNode =
   result.typ = g.sysTypeFromName(n.info, "RootEffect")
   if not n.isNil: result.info = n.info
 
-proc addEffect(a: PEffects, e, comesFrom: PNode) =
+proc addRaiseEffect(a: PEffects, e, comesFrom: PNode) =
   assert e.kind != nkRaiseStmt
   var aa = a.exc
   for i in a.bottom..<aa.len:
@@ -345,11 +345,11 @@ proc addTag(a: PEffects, e, comesFrom: PNode) =
     if sameType(aa[i].typ.skipTypes(skipPtrs), e.typ.skipTypes(skipPtrs)): return
   throws(a.tags, e, comesFrom)
 
-proc mergeEffects(a: PEffects, b, comesFrom: PNode) =
+proc mergeRaises(a: PEffects, b, comesFrom: PNode) =
   if b.isNil:
-    addEffect(a, createRaise(a.graph, comesFrom), comesFrom)
+    addRaiseEffect(a, createRaise(a.graph, comesFrom), comesFrom)
   else:
-    for effect in items(b): addEffect(a, effect, comesFrom)
+    for effect in items(b): addRaiseEffect(a, effect, comesFrom)
 
 proc mergeTags(a: PEffects, b, comesFrom: PNode) =
   if b.isNil:
@@ -489,7 +489,7 @@ proc mergeLockLevels(tracked: PEffects, n: PNode, lockLevel: TLockLevel) =
 proc propagateEffects(tracked: PEffects, n: PNode, s: PSym) =
   let pragma = s.ast[pragmasPos]
   let spec = effectSpec(pragma, wRaises)
-  mergeEffects(tracked, spec, n)
+  mergeRaises(tracked, spec, n)
 
   let tagSpec = effectSpec(pragma, wTags)
   mergeTags(tracked, tagSpec, n)
@@ -535,7 +535,7 @@ proc notNilCheck(tracked: PEffects, n: PNode, paramType: PType) =
     of impYes: discard
 
 proc assumeTheWorst(tracked: PEffects; n: PNode; op: PType) =
-  addEffect(tracked, createRaise(tracked.graph, n), nil)
+  addRaiseEffect(tracked, createRaise(tracked.graph, n), nil)
   addTag(tracked, createTag(tracked.graph, n), nil)
   let lockLevel = if op.lockLevel == UnspecifiedLockLevel: UnknownLockLevel
                   else: op.lockLevel
@@ -581,7 +581,7 @@ proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, paramType: PType;
       elif tfNoSideEffect notin op.flags and not isOwnedProcVar(a, tracked.owner):
         markSideEffect(tracked, a)
     else:
-      mergeEffects(tracked, effectList[exceptionEffects], n)
+      mergeRaises(tracked, effectList[exceptionEffects], n)
       mergeTags(tracked, effectList[tagEffects], n)
       if notGcSafe(op):
         if tracked.config.hasWarn(warnGcUnsafe): warnAboutGcUnsafe(n, tracked.config)
@@ -780,7 +780,7 @@ proc trackCall(tracked: PEffects; n: PNode) =
         assumeTheWorst(tracked, n, op)
         gcsafeAndSideeffectCheck()
     else:
-      mergeEffects(tracked, effectList[exceptionEffects], n)
+      mergeRaises(tracked, effectList[exceptionEffects], n)
       mergeTags(tracked, effectList[tagEffects], n)
       gcsafeAndSideeffectCheck()
   if a.kind != nkSym or a.sym.magic != mNBindSym:
@@ -837,6 +837,64 @@ proc trackCall(tracked: PEffects; n: PNode) =
       # initVar(tracked, n[i].skipAddr, false)
       else: discard
 
+type
+  PragmaBlockContext = object
+    oldLocked: int
+    oldLockLevel: TLockLevel
+    enforcedGcSafety, enforceNoSideEffects: bool
+    oldExc, oldTags: int
+    exc, tags: PNode
+
+proc createBlockContext(tracked: PEffects): PragmaBlockContext =
+  result = PragmaBlockContext(oldLocked: tracked.locked.len,
+    oldLockLevel: tracked.currLockLevel,
+    enforcedGcSafety: false, enforceNoSideEffects: false,
+    oldExc: tracked.exc.len, oldTags: tracked.tags.len)
+
+proc applyBlockContext(tracked: PEffects, bc: PragmaBlockContext) =
+  if bc.enforcedGcSafety: tracked.inEnforcedGcSafe = true
+  if bc.enforceNoSideEffects: tracked.inEnforcedNoSideEffects = true
+
+proc unapplyBlockContext(tracked: PEffects; bc: PragmaBlockContext) =
+  if bc.enforcedGcSafety: tracked.inEnforcedGcSafe = false
+  if bc.enforceNoSideEffects: tracked.inEnforcedNoSideEffects = false
+  setLen(tracked.locked, bc.oldLocked)
+  tracked.currLockLevel = bc.oldLockLevel
+  if bc.exc != nil:
+    # beware that 'raises: []' is very different from not saying
+    # anything about 'raises' in the 'cast' at all. Same applies for 'tags'.
+    setLen(tracked.exc.sons, bc.oldExc)
+    for e in bc.exc:
+      addRaiseEffect(tracked, e, e)
+  if bc.tags != nil:
+    setLen(tracked.tags.sons, bc.oldTags)
+    for t in bc.tags:
+      addTag(tracked, t, t)
+
+proc castBlock(tracked: PEffects, pragma: PNode, bc: var PragmaBlockContext) =
+  case whichPragma(pragma)
+  of wGcSafe:
+    bc.enforcedGcSafety = true
+  of wNoSideEffect:
+    bc.enforceNoSideEffects = true
+  of wTags:
+    let n = pragma[1]
+    if n.kind in {nkCurly, nkBracket}:
+      bc.tags = n
+    else:
+      bc.tags = newNodeI(nkArgList, pragma.info)
+      bc.tags.add n
+  of wRaises:
+    let n = pragma[1]
+    if n.kind in {nkCurly, nkBracket}:
+      bc.exc = n
+    else:
+      bc.exc = newNodeI(nkArgList, pragma.info)
+      bc.exc.add n
+  else:
+    localError(tracked.config, pragma.info,
+        "invalid pragma block: " & $pragma)
+
 proc track(tracked: PEffects, n: PNode) =
   case n.kind
   of nkSym:
@@ -854,7 +912,7 @@ proc track(tracked: PEffects, n: PNode) =
     if n[0].kind != nkEmpty:
       n[0].info = n.info
       #throws(tracked.exc, n[0])
-      addEffect(tracked, n[0], nil)
+      addRaiseEffect(tracked, n[0], nil)
       for i in 0..<n.safeLen:
         track(tracked, n[i])
       createTypeBoundOps(tracked, n[0].typ, n.info)
@@ -862,7 +920,7 @@ proc track(tracked: PEffects, n: PNode) =
       # A `raise` with no arguments means we're going to re-raise the exception
       # being handled or, if outside of an `except` block, a `ReraiseDefect`.
       # Here we add a `Exception` tag in order to cover both the cases.
-      addEffect(tracked, createRaise(tracked.graph, n), nil)
+      addRaiseEffect(tracked, createRaise(tracked.graph, n), nil)
   of nkCallKinds:
     trackCall(tracked, n)
   of nkDotExpr:
@@ -1011,26 +1069,24 @@ proc track(tracked: PEffects, n: PNode) =
       checkForSink(tracked.config, tracked.owner, n[i])
   of nkPragmaBlock:
     let pragmaList = n[0]
-    let oldLocked = tracked.locked.len
-    let oldLockLevel = tracked.currLockLevel
-    var enforcedGcSafety = false
-    var enforceNoSideEffects = false
+    var bc = createBlockContext(tracked)
     for i in 0..<pragmaList.len:
       let pragma = whichPragma(pragmaList[i])
-      if pragma == wLocks:
+      case pragma
+      of wLocks:
         lockLocations(tracked, pragmaList[i])
-      elif pragma == wGcSafe:
-        enforcedGcSafety = true
-      elif pragma == wNoSideEffect:
-        enforceNoSideEffects = true
-
-    if enforcedGcSafety: tracked.inEnforcedGcSafe = true
-    if enforceNoSideEffects: tracked.inEnforcedNoSideEffects = true
+      of wGcSafe:
+        bc.enforcedGcSafety = true
+      of wNoSideEffect:
+        bc.enforceNoSideEffects = true
+      of wCast:
+        castBlock(tracked, pragmaList[i][1], bc)
+      else:
+        discard
+    applyBlockContext(tracked, bc)
     track(tracked, n.lastSon)
-    if enforcedGcSafety: tracked.inEnforcedGcSafe = false
-    if enforceNoSideEffects: tracked.inEnforcedNoSideEffects = false
-    setLen(tracked.locked, oldLocked)
-    tracked.currLockLevel = oldLockLevel
+    unapplyBlockContext(tracked, bc)
+
   of nkTypeSection, nkProcDef, nkConverterDef, nkMethodDef, nkIteratorDef,
       nkMacroDef, nkTemplateDef, nkLambda, nkDo, nkFuncDef:
     discard

compiler/semstmts.nim

@@ -2169,7 +2169,7 @@ proc setLine(n: PNode, info: TLineInfo) =
 proc semPragmaBlock(c: PContext, n: PNode): PNode =
   checkSonsLen(n, 2, c.config)
   let pragmaList = n[0]
-  pragma(c, nil, pragmaList, exprPragmas)
+  pragma(c, nil, pragmaList, exprPragmas, isStatement = true)
   n[1] = semExpr(c, n[1])
   result = n
   result.typ = n[1].typ

compiler/transf.nim

@@ -1009,6 +1009,7 @@ proc transform(c: PTransf, n: PNode): PNode =
   # Constants can be inlined here, but only if they cannot result in a cast
   # in the back-end (e.g. var p: pointer = someProc)
   let exprIsPointerCast = n.kind in {nkCast, nkConv, nkHiddenStdConv} and
+                          n.typ != nil and
                           n.typ.kind == tyPointer
   if not exprIsPointerCast:
     var cnst = getConstExpr(c.module, result, c.graph)

compiler/trees.nim

@@ -130,7 +130,19 @@ proc isRange*(n: PNode): bool {.inline.} =
 
 proc whichPragma*(n: PNode): TSpecialWord =
   let key = if n.kind in nkPragmaCallKinds and n.len > 0: n[0] else: n
-  if key.kind == nkIdent: result = whichKeyword(key.ident)
+  case key.kind
+  of nkIdent: result = whichKeyword(key.ident)
+  of nkSym: result = whichKeyword(key.sym.name)
+  of nkCast: result = wCast
+  of nkClosedSymChoice, nkOpenSymChoice:
+    result = whichPragma(key[0])
+  else: result = wInvalid
+
+proc isNoSideEffectPragma*(n: PNode): bool =
+  var k = whichPragma(n)
+  if k == wCast:
+    k = whichPragma(n[1])
+  result = k == wNoSideEffect
 
 proc findPragma*(n: PNode, which: TSpecialWord): PNode =
   if n.kind == nkPragma:

compiler/varpartitions.nim

@@ -29,8 +29,7 @@
 ## for a high-level description of how borrow checking works.
 
 import ast, types, lineinfos, options, msgs, renderer, typeallowed
-from trees import getMagic, whichPragma, stupidStmtListExpr
-from wordrecg import wNoSideEffect
+from trees import getMagic, isNoSideEffectPragma, stupidStmtListExpr
 from isolation_check import canAlias
 
 type
@@ -713,7 +712,7 @@ proc traverse(c: var Partitions; n: PNode) =
     let pragmaList = n[0]
     var enforceNoSideEffects = 0
     for i in 0..<pragmaList.len:
-      if whichPragma(pragmaList[i]) == wNoSideEffect:
+      if isNoSideEffectPragma(pragmaList[i]):
         enforceNoSideEffects = 1
         break
 

compiler/vmops.nim

@@ -262,11 +262,25 @@ proc registerAdditionalOps*(c: PCtx) =
     registerCallback c, "stdlib.times.getTime", proc (a: VmArgs) {.nimcall.} =
       setResult(a, times.getTime().toLit)
 
-  registerCallback c, "stdlib.effecttraits.getRaisesListImpl", proc (a: VmArgs) =
+  proc getEffectList(c: PCtx; a: VmArgs; effectIndex: int) =
     let fn = getNode(a, 0)
     if fn.typ != nil and fn.typ.n != nil and fn.typ.n[0].len >= effectListLen and
-        fn.typ.n[0][exceptionEffects] != nil:
+        fn.typ.n[0][effectIndex] != nil:
       var list = newNodeI(nkBracket, fn.info)
-      for e in fn.typ.n[0][exceptionEffects]:
+      for e in fn.typ.n[0][effectIndex]:
         list.add opMapTypeInstToAst(c.cache, e.typ.skipTypes({tyRef}), e.info)
       setResult(a, list)
+
+  registerCallback c, "stdlib.effecttraits.getRaisesListImpl", proc (a: VmArgs) =
+    getEffectList(c, a, exceptionEffects)
+  registerCallback c, "stdlib.effecttraits.getTagsListImpl", proc (a: VmArgs) =
+    getEffectList(c, a, tagEffects)
+
+  registerCallback c, "stdlib.effecttraits.isGcSafeImpl", proc (a: VmArgs) =
+    let fn = getNode(a, 0)
+    setResult(a, fn.typ != nil and tfGcSafe in fn.typ.flags)
+
+  registerCallback c, "stdlib.effecttraits.hasNoSideEffectsImpl", proc (a: VmArgs) =
+    let fn = getNode(a, 0)
+    setResult(a, (fn.typ != nil and tfNoSideEffect in fn.typ.flags) or
+                 (fn.kind == nkSym and fn.sym.kind == skFunc))