strict effects (#18777)

* fixes #17369
* megatest is green for --cpu:arm64
* docgen output includes more tags/raises
* implemented 'effectsOf' 
* algorithm.nim: uses new effectsOf annotation
* closes #18376
* closes #17475
* closes #13905
* allow effectsOf: [a, b]
* added a test case
* parameters that are not ours cannot be declared as .effectsOf
* documentation
* manual: added the 'sort' example
* bootstrap with the new better options

16 files changed, 164 insertions, 54 deletions

diff --git a/compiler/ast.nim b/compiler/ast.nim
index 5893a5671..50d048edd 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -229,7 +229,7 @@ type
   TNodeKinds* = set[TNodeKind]
 
 type
-  TSymFlag* = enum    # 47 flags!
+  TSymFlag* = enum    # 48 flags!
     sfUsed,           # read access of sym (for warnings) or simply used
     sfExported,       # symbol is exported from module
     sfFromGeneric,    # symbol is instantiation of a generic; this is needed
@@ -299,6 +299,7 @@ type
     sfUsedInFinallyOrExcept  # symbol is used inside an 'except' or 'finally'
     sfSingleUsedTemp  # For temporaries that we know will only be used once
     sfNoalias         # 'noalias' annotation, means C's 'restrict'
+    sfEffectsDelayed  # an 'effectsDelayed' parameter
 
   TSymFlags* = set[TSymFlag]
 
@@ -568,6 +569,7 @@ type
       # sizeof, alignof, offsetof at CT
     tfExplicitCallConv
     tfIsConstructor
+    tfEffectSystemWorkaround
 
   TTypeFlags* = set[TTypeFlag]
 
@@ -1781,7 +1783,7 @@ proc containsNode*(n: PNode, kinds: TNodeKinds): bool =
 
 proc hasSubnodeWith*(n: PNode, kind: TNodeKind): bool =
   case n.kind
-  of nkEmpty..nkNilLit: result = n.kind == kind
+  of nkEmpty..nkNilLit, nkFormalParams: result = n.kind == kind
   else:
     for i in 0..<n.len:
       if (n[i].kind == kind) or hasSubnodeWith(n[i], kind):
diff --git a/compiler/ccgcalls.nim b/compiler/ccgcalls.nim
index 749a7a3b6..828e666a8 100644
--- a/compiler/ccgcalls.nim
+++ b/compiler/ccgcalls.nim
@@ -325,7 +325,7 @@ proc skipTrivialIndirections(n: PNode): PNode =
 
 proc getPotentialWrites(n: PNode; mutate: bool; result: var seq[PNode]) =
   case n.kind:
-  of nkLiterals, nkIdent: discard
+  of nkLiterals, nkIdent, nkFormalParams: discard
   of nkSym:
     if mutate: result.add n
   of nkAsgn, nkFastAsgn:
@@ -354,7 +354,7 @@ proc getPotentialWrites(n: PNode; mutate: bool; result: var seq[PNode]) =
 
 proc getPotentialReads(n: PNode; result: var seq[PNode]) =
   case n.kind:
-  of nkLiterals, nkIdent: discard
+  of nkLiterals, nkIdent, nkFormalParams: discard
   of nkSym: result.add n
   else:
     for s in n:
diff --git a/compiler/commands.nim b/compiler/commands.nim
index 079717862..9b7e35791 100644
--- a/compiler/commands.nim
+++ b/compiler/commands.nim
@@ -8,7 +8,6 @@
 #
 
 # This module handles the parsing of command line arguments.
-from ast import setUseIc
 
 # We do this here before the 'import' statement so 'defined' does not get
 # confused with 'TGCMode.gcMarkAndSweep' etc.
@@ -30,7 +29,7 @@ import
   msgs, options, nversion, condsyms, extccomp, platform,
   wordrecg, nimblecmd, lineinfos, pathutils, pathnorm
 
-from ast import eqTypeFlags, tfGcSafe, tfNoSideEffect
+from ast import setUseIc, eqTypeFlags, tfGcSafe, tfNoSideEffect
 
 # but some have deps to imported modules. Yay.
 bootSwitch(usedTinyC, hasTinyCBackend, "-d:tinyc")
diff --git a/compiler/condsyms.nim b/compiler/condsyms.nim
index 33cd1818b..df355bc26 100644
--- a/compiler/condsyms.nim
+++ b/compiler/condsyms.nim
@@ -137,3 +137,4 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimHasDragonBox")
   defineSymbol("nimHasHintAll")
   defineSymbol("nimHasTrace")
+  defineSymbol("nimHasEffectsOf")
diff --git a/compiler/docgen.nim b/compiler/docgen.nim
index 706b54bcd..1acfc7489 100644
--- a/compiler/docgen.nim
+++ b/compiler/docgen.nim
@@ -1085,10 +1085,11 @@ proc documentEffect(cache: IdentCache; n, x: PNode, effectType: TSpecialWord, id
     let actual = s.typ.n[0]
     if actual.len != effectListLen: return
     let real = actual[idx]
-
+    if real == nil: return
+    let realLen = real.len
     # warning: hack ahead:
-    var effects = newNodeI(nkBracket, n.info, real.len)
-    for i in 0..<real.len:
+    var effects = newNodeI(nkBracket, n.info, realLen)
+    for i in 0..<realLen:
       var t = typeToString(real[i].typ)
       if t.startsWith("ref "): t = substr(t, 4)
       effects[i] = newIdentNode(getIdent(cache, t), n.info)
diff --git a/compiler/lineinfos.nim b/compiler/lineinfos.nim
index fd7ce0c04..8bd5a0890 100644
--- a/compiler/lineinfos.nim
+++ b/compiler/lineinfos.nim
@@ -75,6 +75,7 @@ type
     warnAnyEnumConv = "AnyEnumConv",
     warnHoleEnumConv = "HoleEnumConv",
     warnCstringConv = "CStringConv",
+    warnEffect = "Effect",
     warnUser = "User",
     # hints
     hintSuccess = "Success", hintSuccessX = "SuccessX",
@@ -163,6 +164,7 @@ const
     warnAnyEnumConv: "$1",
     warnHoleEnumConv: "$1",
     warnCstringConv: "$1",
+    warnEffect: "$1",
     warnUser: "$1",
     hintSuccess: "operation successful: $#",
     # keep in sync with `testament.isSuccess`
diff --git a/compiler/nim.cfg b/compiler/nim.cfg
index ec51bd463..d6ac6a937 100644
--- a/compiler/nim.cfg
+++ b/compiler/nim.cfg
@@ -25,3 +25,8 @@ define:useStdoutAsStdmsg
 @if nimHasWarningObservableStores:
   warning:ObservableStores: off
 @end
+
+@if nimHasEffectsOf:
+  experimental:strictEffects
+  warningAsError:Effect:on
+@end
diff --git a/compiler/options.nim b/compiler/options.nim
index e37dea1b6..89a16a49c 100644
--- a/compiler/options.nim
+++ b/compiler/options.nim
@@ -204,7 +204,8 @@ type
     strictFuncs,
     views,
     strictNotNil,
-    overloadableEnums
+    overloadableEnums,
+    strictEffects
 
   LegacyFeature* = enum
     allowSemcheckedAstModification,
diff --git a/compiler/pragmas.nim b/compiler/pragmas.nim
index 6637a8673..e9f52c71f 100644
--- a/compiler/pragmas.nim
+++ b/compiler/pragmas.nim
@@ -29,7 +29,7 @@ const
     wCompilerProc, wNonReloadable, wCore, wProcVar, wVarargs, wCompileTime, wMerge,
     wBorrow, wImportCompilerProc, wThread,
     wAsmNoStackFrame, wDiscardable, wNoInit, wCodegenDecl,
-    wGensym, wInject, wRaises, wTags, wLocks, wDelegator, wGcSafe,
+    wGensym, wInject, wRaises, wEffectsOf, wTags, wLocks, wDelegator, wGcSafe,
     wConstructor, wLiftLocals, wStackTrace, wLineTrace, wNoDestroy,
     wRequires, wEnsures}
   converterPragmas* = procPragmas
@@ -41,7 +41,7 @@ const
     wDiscardable, wGensym, wInject, wDelegator}
   iteratorPragmas* = declPragmas + {FirstCallConv..LastCallConv, wNoSideEffect, wSideEffect,
     wMagic, wBorrow,
-    wDiscardable, wGensym, wInject, wRaises,
+    wDiscardable, wGensym, wInject, wRaises, wEffectsOf,
     wTags, wLocks, wGcSafe, wRequires, wEnsures}
   exprPragmas* = {wLine, wLocks, wNoRewrite, wGcSafe, wNoSideEffect}
   stmtPragmas* = {wChecks, wObjChecks, wFieldChecks, wRangeChecks,
@@ -59,7 +59,7 @@ const
   lambdaPragmas* = {FirstCallConv..LastCallConv,
     wNoSideEffect, wSideEffect, wNoreturn, wNosinks, wDynlib, wHeader,
     wThread, wAsmNoStackFrame,
-    wRaises, wLocks, wTags, wRequires, wEnsures,
+    wRaises, wLocks, wTags, wRequires, wEnsures, wEffectsOf,
     wGcSafe, wCodegenDecl, wNoInit, wCompileTime}
   typePragmas* = declPragmas + {wMagic, wAcyclic,
     wPure, wHeader, wCompilerProc, wCore, wFinal, wSize, wShallow,
@@ -79,7 +79,7 @@ const
   paramPragmas* = {wNoalias, wInject, wGensym}
   letPragmas* = varPragmas
   procTypePragmas* = {FirstCallConv..LastCallConv, wVarargs, wNoSideEffect,
-                      wThread, wRaises, wLocks, wTags, wGcSafe,
+                      wThread, wRaises, wEffectsOf, wLocks, wTags, wGcSafe,
                       wRequires, wEnsures}
   forVarPragmas* = {wInject, wGensym}
   allRoutinePragmas* = methodPragmas + iteratorPragmas + lambdaPragmas
@@ -779,6 +779,26 @@ proc semCustomPragma(c: PContext, n: PNode): PNode =
     # pragma(arg) -> pragma: arg
     result.transitionSonsKind(n.kind)
 
+proc processEffectsOf(c: PContext, n: PNode; owner: PSym) =
+  proc processParam(c: PContext; n: PNode) =
+    let r = c.semExpr(c, n)
+    if r.kind == nkSym and r.sym.kind == skParam:
+      if r.sym.owner == owner:
+        incl r.sym.flags, sfEffectsDelayed
+      else:
+        localError(c.config, n.info, errGenerated, "parameter cannot be declared as .effectsOf")
+    else:
+      localError(c.config, n.info, errGenerated, "parameter name expected")
+
+  if n.kind notin nkPragmaCallKinds or n.len != 2:
+    localError(c.config, n.info, errGenerated, "parameter name expected")
+  else:
+    let it = n[1]
+    if it.kind in {nkCurly, nkBracket}:
+      for x in items(it): processParam(c, x)
+    else:
+      processParam(c, it)
+
 proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
                   validPragmas: TSpecialWords,
                   comesFromPush, isStatement: bool): bool =
@@ -895,6 +915,8 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
       of wNoalias:
         noVal(c, it)
         incl(sym.flags, sfNoalias)
+      of wEffectsOf:
+        processEffectsOf(c, it, sym)
       of wThreadVar:
         noVal(c, it)
         incl(sym.flags, {sfThread, sfGlobal})
diff --git a/compiler/sem.nim b/compiler/sem.nim
index 804325e56..24709cf21 100644
--- a/compiler/sem.nim
+++ b/compiler/sem.nim
@@ -400,9 +400,10 @@ when not defined(nimHasSinkInference):
 include hlo, seminst, semcall
 
 proc resetSemFlag(n: PNode) =
-  excl n.flags, nfSem
-  for i in 0..<n.safeLen:
-    resetSemFlag(n[i])
+  if n != nil:
+    excl n.flags, nfSem
+    for i in 0..<n.safeLen:
+      resetSemFlag(n[i])
 
 proc semAfterMacroCall(c: PContext, call, macroResult: PNode,
                        s: PSym, flags: TExprFlags): PNode =
diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index 2478420f7..a3064788e 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -152,6 +152,8 @@ proc effectProblem(f, a: PType; result: var string; c: PContext) =
       of efLockLevelsDiffer:
         result.add "\n  The `.locks` requirements differ. Annotate the " &
             "proc with {.locks: 0.} to get extended error information."
+      of efEffectsDelayed:
+        result.add "\n  The `.effectsOf` annotations differ."
       when defined(drnim):
         if not c.graph.compatibleProps(c.graph, f, a):
           result.add "\n  The `.requires` or `.ensures` properties are incompatible."
diff --git a/compiler/semdata.nim b/compiler/semdata.nim
index 0a6d09a56..31affb24f 100644
--- a/compiler/semdata.nim
+++ b/compiler/semdata.nim
@@ -261,7 +261,9 @@ proc getGenSym*(c: PContext; s: PSym): PSym =
   result = s
 
 proc considerGenSyms*(c: PContext; n: PNode) =
-  if n.kind == nkSym:
+  if n == nil:
+    discard "can happen for nkFormalParams/nkArgList"
+  elif n.kind == nkSym:
     let s = getGenSym(c, n.sym)
     if n.sym != s:
       n.sym = s
diff --git a/compiler/sempass2.nim b/compiler/sempass2.nim
index e2f85dd38..b584bb232 100644
--- a/compiler/sempass2.nim
+++ b/compiler/sempass2.nim
@@ -296,11 +296,12 @@ proc useVarNoInitCheck(a: PEffects; n: PNode; s: PSym) =
   if {sfGlobal, sfThread} * s.flags != {} and s.kind in {skVar, skLet} and
       s.magic != mNimvm:
     if s.guard != nil: guardGlobal(a, n, s.guard)
-    if {sfGlobal, sfThread} * s.flags == {sfGlobal} and
-        (tfHasGCedMem in s.typ.flags or s.typ.isGCedMem):
-      #if a.config.hasWarn(warnGcUnsafe): warnAboutGcUnsafe(n)
-      markGcUnsafe(a, s)
-    markSideEffect(a, s, n.info)
+    if strictEffects notin a.c.features:
+      if {sfGlobal, sfThread} * s.flags == {sfGlobal} and
+          (tfHasGCedMem in s.typ.flags or s.typ.isGCedMem):
+        #if a.config.hasWarn(warnGcUnsafe): warnAboutGcUnsafe(n)
+        markGcUnsafe(a, s)
+      markSideEffect(a, s, n.info)
   if s.owner != a.owner and s.kind in {skVar, skLet, skForVar, skResult, skParam} and
      {sfGlobal, sfThread} * s.flags == {}:
     a.isInnerProc = true
@@ -474,14 +475,20 @@ proc trackTryStmt(tracked: PEffects, n: PNode) =
   for id, count in items(inter):
     if count == branches: tracked.init.add id
 
-proc isIndirectCall(n: PNode, owner: PSym): bool =
+proc isIndirectCall(tracked: PEffects; n: PNode): bool =
   # we don't count f(...) as an indirect call if 'f' is an parameter.
   # Instead we track expressions of type tyProc too. See the manual for
   # details:
   if n.kind != nkSym:
     result = true
   elif n.sym.kind == skParam:
-    result = owner != n.sym.owner or owner == nil
+    if strictEffects in tracked.c.features:
+      if tracked.owner == n.sym.owner and sfEffectsDelayed in n.sym.flags:
+        result = false # it is not a harmful call
+      else:
+        result = true
+    else:
+      result = tracked.owner != n.sym.owner or tracked.owner == nil
   elif n.sym.kind notin routineKinds:
     result = true
 
@@ -579,9 +586,14 @@ proc assumeTheWorst(tracked: PEffects; n: PNode; op: PType) =
   #  message(??.config, n.info, warnUser, "had to assume the worst here")
   mergeLockLevels(tracked, n, lockLevel)
 
-proc isOwnedProcVar(n: PNode; owner: PSym): bool =
+proc isOwnedProcVar(tracked: PEffects; n: PNode): bool =
   # XXX prove the soundness of this effect system rule
-  result = n.kind == nkSym and n.sym.kind == skParam and owner == n.sym.owner
+  result = n.kind == nkSym and n.sym.kind == skParam and
+    tracked.owner == n.sym.owner
+  #if result and sfPolymorphic notin n.sym.flags:
+  #  echo tracked.config $ n.info, " different here!"
+  if strictEffects in tracked.c.features:
+    result = result and sfEffectsDelayed in n.sym.flags
 
 proc isNoEffectList(n: PNode): bool {.inline.} =
   assert n.kind == nkEffectList
@@ -590,11 +602,15 @@ proc isNoEffectList(n: PNode): bool {.inline.} =
 proc isTrival(caller: PNode): bool {.inline.} =
   result = caller.kind == nkSym and caller.sym.magic in {mEqProc, mIsNil, mMove, mWasMoved, mSwap}
 
-proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, paramType: PType; caller: PNode) =
+proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, formals: PType; argIndex: int; caller: PNode) =
   let a = skipConvCastAndClosure(n)
   let op = a.typ
+  let param = if formals != nil and argIndex < formals.len and formals.n != nil: formals.n[argIndex].sym else: nil
   # assume indirect calls are taken here:
-  if op != nil and op.kind == tyProc and n.skipConv.kind != nkNilLit and not isTrival(caller):
+  if op != nil and op.kind == tyProc and n.skipConv.kind != nkNilLit and
+      not isTrival(caller) and
+      ((param != nil and sfEffectsDelayed in param.flags) or strictEffects notin tracked.c.features):
+
     internalAssert tracked.config, op.n[0].kind == nkEffectList
     var effectList = op.n[0]
     var s = n.skipConv
@@ -607,14 +623,14 @@ proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, paramType: PType;
         # we have no explicit effects but it's a forward declaration and so it's
         # stated there are no additional effects, so simply propagate them:
         propagateEffects(tracked, n, n.sym)
-      elif not isOwnedProcVar(a, tracked.owner):
+      elif not isOwnedProcVar(tracked, a):
         # we have no explicit effects so assume the worst:
         assumeTheWorst(tracked, n, op)
       # assume GcUnsafe unless in its type; 'forward' does not matter:
-      if notGcSafe(op) and not isOwnedProcVar(a, tracked.owner):
+      if notGcSafe(op) and not isOwnedProcVar(tracked, a):
         if tracked.config.hasWarn(warnGcUnsafe): warnAboutGcUnsafe(n, tracked.config)
         markGcUnsafe(tracked, a)
-      elif tfNoSideEffect notin op.flags and not isOwnedProcVar(a, tracked.owner):
+      elif tfNoSideEffect notin op.flags and not isOwnedProcVar(tracked, a):
         markSideEffect(tracked, a, n.info)
     else:
       mergeRaises(tracked, effectList[exceptionEffects], n)
@@ -624,6 +640,7 @@ proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, paramType: PType;
         markGcUnsafe(tracked, a)
       elif tfNoSideEffect notin op.flags:
         markSideEffect(tracked, a, n.info)
+  let paramType = if formals != nil and argIndex < formals.len: formals[argIndex] else: nil
   if paramType != nil and paramType.kind in {tyVar}:
     invalidateFacts(tracked.guards, n)
     if n.kind == nkSym and isLocalVar(tracked, n.sym):
@@ -724,9 +741,6 @@ proc trackBlock(tracked: PEffects, n: PNode) =
   else:
     track(tracked, n)
 
-proc paramType(op: PType, i: int): PType =
-  if op != nil and i < op.len: result = op[i]
-
 proc cstringCheck(tracked: PEffects; n: PNode) =
   if n[0].typ.kind == tyCstring and (let a = skipConv(n[1]);
       a.typ.kind == tyString and a.kind notin {nkStrLit..nkTripleStrLit}):
@@ -770,6 +784,25 @@ proc checkRange(c: PEffects; value: PNode; typ: PType) =
     checkLe(c, lowBound, value)
     checkLe(c, value, highBound)
 
+#[
+proc passedToEffectsDelayedParam(tracked: PEffects; n: PNode) =
+  let t = n.typ.skipTypes(abstractInst)
+  if t.kind == tyProc:
+    if n.kind == nkSym and tracked.owner == n.sym.owner and sfEffectsDelayed in n.sym.flags:
+      discard "the arg is itself a delayed parameter, so do nothing"
+    else:
+      var effectList = t.n[0]
+      if effectList.len == effectListLen:
+        mergeRaises(tracked, effectList[exceptionEffects], n)
+        mergeTags(tracked, effectList[tagEffects], n)
+      if not importedFromC(n):
+        if notGcSafe(t):
+          if tracked.config.hasWarn(warnGcUnsafe): warnAboutGcUnsafe(n, tracked.config)
+          markGcUnsafe(tracked, n)
+        if tfNoSideEffect notin t.flags:
+          markSideEffect(tracked, n, n.info)
+]#
+
 proc trackCall(tracked: PEffects; n: PNode) =
   template gcsafeAndSideeffectCheck() =
     if notGcSafe(op) and not importedFromC(a):
@@ -811,7 +844,7 @@ proc trackCall(tracked: PEffects; n: PNode) =
       elif isNoEffectList(effectList):
         if isForwardedProc(a):
           propagateEffects(tracked, n, a.sym)
-        elif isIndirectCall(a, tracked.owner):
+        elif isIndirectCall(tracked, a):
           assumeTheWorst(tracked, n, op)
           gcsafeAndSideeffectCheck()
       else:
@@ -819,7 +852,8 @@ proc trackCall(tracked: PEffects; n: PNode) =
         mergeTags(tracked, effectList[tagEffects], n)
         gcsafeAndSideeffectCheck()
     if a.kind != nkSym or a.sym.magic != mNBindSym:
-      for i in 1..<n.len: trackOperandForIndirectCall(tracked, n[i], paramType(op, i), a)
+      for i in 1..<n.len:
+        trackOperandForIndirectCall(tracked, n[i], op, i, a)
     if a.kind == nkSym and a.sym.magic in {mNew, mNewFinalize, mNewSeq}:
       # may not look like an assignment, but it is:
       let arg = n[1]
@@ -1225,7 +1259,7 @@ proc subtypeRelation(g: ModuleGraph; spec, real: PNode): bool =
   else:
     return safeInheritanceDiff(g.excType(real), spec.typ) <= 0
 
-proc checkRaisesSpec(g: ModuleGraph; spec, real: PNode, msg: string, hints: bool;
+proc checkRaisesSpec(g: ModuleGraph; emitWarnings: bool; spec, real: PNode, msg: string, hints: bool;
                      effectPredicate: proc (g: ModuleGraph; a, b: PNode): bool {.nimcall.};
                      hintsArg: PNode = nil) =
   # check that any real exception is listed in 'spec'; mark those as used;
@@ -1241,7 +1275,8 @@ proc checkRaisesSpec(g: ModuleGraph; spec, real: PNode, msg: string, hints: bool
       pushInfoContext(g.config, spec.info)
       var rr = if r.kind == nkRaiseStmt: r[0] else: r
       while rr.kind in {nkStmtList, nkStmtListExpr} and rr.len > 0: rr = rr.lastSon
-      localError(g.config, r.info, errGenerated, renderTree(rr) & " " & msg & typeToString(r.typ))
+      message(g.config, r.info, if emitWarnings: warnEffect else: errGenerated,
+              renderTree(rr) & " " & msg & typeToString(r.typ))
       popInfoContext(g.config)
   # hint about unnecessarily listed exception types:
   if hints:
@@ -1258,11 +1293,11 @@ proc checkMethodEffects*(g: ModuleGraph; disp, branch: PSym) =
   let p = disp.ast[pragmasPos]
   let raisesSpec = effectSpec(p, wRaises)
   if not isNil(raisesSpec):
-    checkRaisesSpec(g, raisesSpec, actual[exceptionEffects],
+    checkRaisesSpec(g, false, raisesSpec, actual[exceptionEffects],
       "can raise an unlisted exception: ", hints=off, subtypeRelation)
   let tagsSpec = effectSpec(p, wTags)
   if not isNil(tagsSpec):
-    checkRaisesSpec(g, tagsSpec, actual[tagEffects],
+    checkRaisesSpec(g, false, tagsSpec, actual[tagEffects],
       "can have an unlisted effect: ", hints=off, subtypeRelation)
   if sfThread in disp.flags and notGcSafe(branch.typ):
     localError(g.config, branch.info, "base method is GC-safe, but '$1' is not" %
@@ -1283,7 +1318,7 @@ proc checkMethodEffects*(g: ModuleGraph; disp, branch: PSym) =
         "base method has lock level $1, but dispatcher has $2" %
           [$branch.typ.lockLevel, $disp.typ.lockLevel])
 
-proc setEffectsForProcType*(g: ModuleGraph; t: PType, n: PNode) =
+proc setEffectsForProcType*(g: ModuleGraph; t: PType, n: PNode; s: PSym = nil) =
   var effects = t.n[0]
   if t.kind != tyProc or effects.kind != nkEffectList: return
   if n.kind != nkEmpty:
@@ -1292,9 +1327,14 @@ proc setEffectsForProcType*(g: ModuleGraph; t: PType, n: PNode) =
     let raisesSpec = effectSpec(n, wRaises)
     if not isNil(raisesSpec):
       effects[exceptionEffects] = raisesSpec
+    elif s != nil and (s.magic != mNone or {sfImportc, sfExportc} * s.flags == {sfImportc}):
+      effects[exceptionEffects] = newNodeI(nkArgList, effects.info)
+
     let tagsSpec = effectSpec(n, wTags)
     if not isNil(tagsSpec):
       effects[tagEffects] = tagsSpec
+    elif s != nil and (s.magic != mNone or {sfImportc, sfExportc} * s.flags == {sfImportc}):
+      effects[tagEffects] = newNodeI(nkArgList, effects.info)
 
     let requiresSpec = propSpec(n, wRequires)
     if not isNil(requiresSpec):
@@ -1304,15 +1344,21 @@ proc setEffectsForProcType*(g: ModuleGraph; t: PType, n: PNode) =
       effects[ensuresEffects] = ensuresSpec
 
     effects[pragmasEffects] = n
+  if s != nil and s.magic != mNone:
+    if s.magic != mEcho:
+      t.flags.incl tfNoSideEffect
 
-proc initEffects(g: ModuleGraph; effects: PNode; s: PSym; t: var TEffects; c: PContext) =
+proc rawInitEffects(g: ModuleGraph; effects: PNode) =
   newSeq(effects.sons, effectListLen)
-  effects[exceptionEffects] = newNodeI(nkArgList, s.info)
-  effects[tagEffects] = newNodeI(nkArgList, s.info)
+  effects[exceptionEffects] = newNodeI(nkArgList, effects.info)
+  effects[tagEffects] = newNodeI(nkArgList, effects.info)
   effects[requiresEffects] = g.emptyNode
   effects[ensuresEffects] = g.emptyNode
   effects[pragmasEffects] = g.emptyNode
 
+proc initEffects(g: ModuleGraph; effects: PNode; s: PSym; t: var TEffects; c: PContext) =
+  rawInitEffects(g, effects)
+
   t.exc = effects[exceptionEffects]
   t.tags = effects[tagEffects]
   t.owner = s
@@ -1341,10 +1387,14 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
   if effects.kind != nkEffectList: return
   # effects already computed?
   if not s.hasRealBody: return
-  if effects.len == effectListLen: return
+  let emitWarnings = tfEffectSystemWorkaround in s.typ.flags
+  if effects.len == effectListLen and not emitWarnings: return
+
+  var inferredEffects = newNodeI(nkEffectList, s.info)
 
   var t: TEffects
-  initEffects(g, effects, s, t, c)
+  initEffects(g, inferredEffects, s, t, c)
+  rawInitEffects g, effects
   track(t, body)
 
   if s.kind != skMacro:
@@ -1369,17 +1419,21 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
   let p = s.ast[pragmasPos]
   let raisesSpec = effectSpec(p, wRaises)
   if not isNil(raisesSpec):
-    checkRaisesSpec(g, raisesSpec, t.exc, "can raise an unlisted exception: ",
+    checkRaisesSpec(g, emitWarnings, raisesSpec, t.exc, "can raise an unlisted exception: ",
                     hints=on, subtypeRelation, hintsArg=s.ast[0])
     # after the check, use the formal spec:
     effects[exceptionEffects] = raisesSpec
+  else:
+    effects[exceptionEffects] = t.exc
 
   let tagsSpec = effectSpec(p, wTags)
   if not isNil(tagsSpec):
-    checkRaisesSpec(g, tagsSpec, t.tags, "can have an unlisted effect: ",
+    checkRaisesSpec(g, emitWarnings, tagsSpec, t.tags, "can have an unlisted effect: ",
                     hints=off, subtypeRelation)
     # after the check, use the formal spec:
     effects[tagEffects] = tagsSpec
+  else:
+    effects[tagEffects] = t.tags
 
   let requiresSpec = propSpec(p, wRequires)
   if not isNil(requiresSpec):
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 14dc89781..df0e2778b 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -1953,6 +1953,10 @@ proc semProcAux(c: PContext, n: PNode, kind: TSymKind,
   if not hasProto:
     implicitPragmas(c, s, n.info, validPragmas)
 
+  if n[pragmasPos].kind != nkEmpty:
+    setEffectsForProcType(c.graph, s.typ, n[pragmasPos], s)
+  s.typ.flags.incl tfEffectSystemWorkaround
+
   # To ease macro generation that produce forwarded .async procs we now
   # allow a bit redundancy in the pragma declarations. The rule is
   # a prototype's pragma list must be a superset of the current pragma
@@ -2211,8 +2215,9 @@ proc evalInclude(c: PContext, n: PNode): PNode =
       incMod(c, n, it, result)
 
 proc setLine(n: PNode, info: TLineInfo) =
-  for i in 0..<n.safeLen: setLine(n[i], info)
-  n.info = info
+  if n != nil:
+    for i in 0..<n.safeLen: setLine(n[i], info)
+    n.info = info
 
 proc semPragmaBlock(c: PContext, n: PNode): PNode =
   checkSonsLen(n, 2, c.config)
diff --git a/compiler/types.nim b/compiler/types.nim
index f0bd99a17..61f563514 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -1364,10 +1364,14 @@ type
     efTagsDiffer
     efTagsUnknown
     efLockLevelsDiffer
+    efEffectsDelayed
 
 proc compatibleEffects*(formal, actual: PType): EffectsCompat =
   # for proc type compatibility checking:
   assert formal.kind == tyProc and actual.kind == tyProc
+  #if tfEffectSystemWorkaround in actual.flags:
+  #  return efCompat
+
   if formal.n[0].kind != nkEffectList or
      actual.n[0].kind != nkEffectList:
     return efTagsUnknown
@@ -1391,9 +1395,17 @@ proc compatibleEffects*(formal, actual: PType): EffectsCompat =
       # spec requires some exception or tag, but we don't know anything:
       if real.len == 0: return efTagsUnknown
       let res = compatibleEffectsAux(st, real[tagEffects])
-      if not res: return efTagsDiffer
+      if not res:
+        #if tfEffectSystemWorkaround notin actual.flags:
+        return efTagsDiffer
   if formal.lockLevel.ord < 0 or
       actual.lockLevel.ord <= formal.lockLevel.ord:
+
+    for i in 1 ..< min(formal.n.len, actual.n.len):
+      if formal.n[i].sym.flags * {sfEffectsDelayed} != actual.n[i].sym.flags * {sfEffectsDelayed}:
+        result = efEffectsDelayed
+        break
+
     result = efCompat
   else:
     result = efLockLevelsDiffer
@@ -1597,7 +1609,8 @@ proc typeMismatch*(conf: ConfigRef; info: TLineInfo, formal, actual: PType, n: P
         msg.add "\n.tag effect is 'any tag allowed'"
       of efLockLevelsDiffer:
         msg.add "\nlock levels differ"
-
+      of efEffectsDelayed:
+        msg.add "\n.effectsOf annotations differ"
     localError(conf, info, msg)
 
 proc isTupleRecursive(t: PType, cycleDetector: var IntSet): bool =
diff --git a/compiler/wordrecg.nim b/compiler/wordrecg.nim
index c3625c5f3..6ff68be75 100644
--- a/compiler/wordrecg.nim
+++ b/compiler/wordrecg.nim
@@ -35,7 +35,7 @@ type
     wMagic = "magic", wThread = "thread", wFinal = "final", wProfiler = "profiler",
     wMemTracker = "memtracker", wObjChecks = "objchecks",
     wIntDefine = "intdefine", wStrDefine = "strdefine", wBoolDefine = "booldefine",
-    wCursor = "cursor", wNoalias = "noalias",
+    wCursor = "cursor", wNoalias = "noalias", wEffectsOf = "effectsOf",
 
     wImmediate = "immediate", wConstructor = "constructor", wDestructor = "destructor",
     wDelegator = "delegator", wOverride = "override", wImportCpp = "importcpp",