alternative, much simpler algorithm for strict func checking (#21066)

* alternative, much simpler algorithm for strict func checking

* forgot to git add new compiler module

* new spec is incredibly simple to describe

* fixes bigints regression

* typos

* closes #16305; closes #17387; closes #20863

compiler/renderer.nim

@@ -1260,8 +1260,12 @@ proc gsub(g: var TSrcGen, n: PNode, c: TContext, fromStmtList = false) =
     gsub(g, n, 0)
   of nkCheckedFieldExpr, nkHiddenAddr, nkHiddenDeref, nkStringToCString, nkCStringToString:
     if renderIds in g.flags:
-      putWithSpace(g, tkAddr, $n.kind)
+      put(g, tkAddr, $n.kind)
+      put(g, tkParLe, "(")
     gsub(g, n, 0)
+    if renderIds in g.flags:
+      put(g, tkParRi, ")")
+
   of nkLambda:
     putWithSpace(g, tkProc, "proc")
     gsub(g, n, paramsPos)

compiler/sempass2.nim

@@ -10,7 +10,8 @@
 import
   intsets, ast, astalgo, msgs, renderer, magicsys, types, idents, trees,
   wordrecg, strutils, options, guards, lineinfos, semfold, semdata,
-  modulegraphs, varpartitions, typeallowed, nilcheck, errorhandling, tables
+  modulegraphs, varpartitions, typeallowed, nilcheck, errorhandling, tables,
+  semstrictfuncs
 
 when defined(nimPreviewSlimSystem):
   import std/assertions
@@ -75,7 +76,7 @@ type
     guards: TModel # nested guards
     locked: seq[PNode] # locked locations
     gcUnsafe, isRecursive, isTopLevel, hasSideEffect, inEnforcedGcSafe: bool
-    hasDangerousAssign, isInnerProc: bool
+    isInnerProc: bool
     inEnforcedNoSideEffects: bool
     currOptions: TOptions
     config: ConfigRef
@@ -817,6 +818,9 @@ proc checkForSink(tracked: PEffects; n: PNode) =
   if tracked.inIfStmt == 0 and optSinkInference in tracked.config.options:
     checkForSink(tracked.config, tracked.c.idgen, tracked.owner, n)
 
+proc strictFuncsActive(tracked: PEffects): bool {.inline.} =
+  sfNoSideEffect in tracked.owner.flags and strictFuncs in tracked.c.features and not tracked.inEnforcedNoSideEffects
+
 proc trackCall(tracked: PEffects; n: PNode) =
   template gcsafeAndSideeffectCheck() =
     if notGcSafe(op) and not importedFromC(a):
@@ -921,12 +925,15 @@ proc trackCall(tracked: PEffects; n: PNode) =
         createTypeBoundOps(tracked, paramType[0], n.info)
         checkForSink(tracked, n[i])
       of tyVar:
-        tracked.hasDangerousAssign = true
         if isOutParam(paramType):
           # consider this case: p(out x, x); we want to remark that 'x' is not
           # initialized until after the call. Since we do this after we analysed the
           # call, this is fine.
           initVar(tracked, n[i].skipAddr, false)
+        if tracked.strictFuncsActive and isDangerousLocation(n[i].skipAddr, tracked.owner):
+          localError(tracked.config, n[i].info,
+            "cannot pass $1 to `var T` parameter within a strict func" % renderTree(n[i]))
+          tracked.hasSideEffect = true
       else: discard
 
 type
@@ -1079,8 +1086,10 @@ proc track(tracked: PEffects, n: PNode) =
       createTypeBoundOps(tracked, n[0].typ, n.info)
     if n[0].kind != nkSym or not isLocalSym(tracked, n[0].sym):
       checkForSink(tracked, n[1])
-      if not tracked.hasDangerousAssign and n[0].kind != nkSym:
-        tracked.hasDangerousAssign = true
+      if tracked.strictFuncsActive and isDangerousLocation(n[0], tracked.owner):
+        tracked.hasSideEffect = true
+        localError(tracked.config, n[0].info,
+            "cannot mutate location $1 within a strict func" % renderTree(n[0]))
   of nkVarSection, nkLetSection:
     for child in n:
       let last = lastSon(child)
@@ -1513,17 +1522,9 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
     effects[ensuresEffects] = ensuresSpec
 
   var mutationInfo = MutationInfo()
-  var hasMutationSideEffect = false
-  if {strictFuncs, views} * c.features != {}:
-    var goals: set[Goal] = {}
-    if strictFuncs in c.features: goals.incl constParameters
-    if views in c.features: goals.incl borrowChecking
-    var partitions = computeGraphPartitions(s, body, g, goals)
-    if not t.hasSideEffect and t.hasDangerousAssign:
-      t.hasSideEffect = varpartitions.hasSideEffect(partitions, mutationInfo)
-      hasMutationSideEffect = t.hasSideEffect
-    if views in c.features:
-      checkBorrowedLocations(partitions, body, g.config)
+  if views in c.features:
+    var partitions = computeGraphPartitions(s, body, g, {borrowChecking})
+    checkBorrowedLocations(partitions, body, g.config)
 
   if sfThread in s.flags and t.gcUnsafe:
     if optThreads in g.config.globalOptions and optThreadAnalysis in g.config.globalOptions:
@@ -1536,9 +1537,7 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
     when false:
       listGcUnsafety(s, onlyWarning=false, g.config)
     else:
-      if hasMutationSideEffect:
-        localError(g.config, s.info, "'$1' can have side effects$2" % [s.name.s, g.config $ mutationInfo])
-      elif c.compilesContextId == 0: # don't render extended diagnostic messages in `system.compiles` context
+      if c.compilesContextId == 0: # don't render extended diagnostic messages in `system.compiles` context
         var msg = ""
         listSideEffects(msg, s, g.config, t.c)
         message(g.config, s.info, errGenerated, msg)

compiler/semstrictfuncs.nim

@@ -0,0 +1,55 @@
+#
+#
+#           The Nim Compiler
+#        (c) Copyright 2022 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## New "strict funcs" checking. Much simpler and hopefully easier to teach than
+## the old but more advanced algorithm that can/could be found in `varpartitions.nim`.
+
+import ast, typeallowed, renderer
+from aliasanalysis import PathKinds0, PathKinds1
+from trees import getMagic
+
+proc isDangerousLocation*(n: PNode; owner: PSym): bool =
+  var n = n
+  var hasDeref = false
+  while true:
+    case n.kind
+    of nkDerefExpr, nkHiddenDeref:
+      if n[0].typ.kind != tyVar:
+        hasDeref = true
+      n = n[0]
+    of PathKinds0 - {nkDerefExpr, nkHiddenDeref}:
+      n = n[0]
+    of PathKinds1:
+      n = n[1]
+    of nkCallKinds:
+      if n.len > 1:
+        if (n.typ != nil and classifyViewType(n.typ) != noView) or getMagic(n) == mSlice:
+          # borrow from first parameter:
+          n = n[1]
+        else:
+          break
+      else:
+        break
+    else:
+      break
+  if n.kind == nkSym:
+    # dangerous if contains a pointer deref or if it doesn't belong to us:
+    result = hasDeref or n.sym.owner != owner
+    when false:
+      # store to something that belongs to a `var` parameter is fine:
+      let s = n.sym
+      if s.kind == skParam:
+        # dangerous unless a `var T` parameter:
+        result = s.typ.kind != tyVar
+      else:
+        # dangerous if contains a pointer deref or if it doesn't belong to us:
+        result = hasDeref or s.owner != owner
+  else:
+    # dangerous if it contains a pointer deref
+    result = hasDeref