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definite assignment analysis for let (#21024)

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* draft for let daa

* patch

* fixes bugs

* errors for global let variable reassignments

* checkpoint

* out param accepts let

* add more tests

* add documentation

* merge tests
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ringabout 2022-12-06 17:19:12 +08:00 • committed by GitHub
commit b2c7019006
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9 changed files with 144 additions and 30 deletions
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32
compiler/sempass2.nim
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@ -84,6 +84,10 @@ type
escapingParams: IntSet
PEffects = var TEffects
const
errXCannotBeAssignedTo = "'$1' cannot be assigned to"
errLetNeedsInit = "'let' symbol requires an initialization"
proc createTypeBoundOps(tracked: PEffects, typ: PType; info: TLineInfo) =
if typ == nil: return
when false:
@ -97,8 +101,8 @@ proc createTypeBoundOps(tracked: PEffects, typ: PType; info: TLineInfo) =
optSeqDestructors in tracked.config.globalOptions:
tracked.owner.flags.incl sfInjectDestructors
proc isLocalVar(a: PEffects, s: PSym): bool =
s.typ != nil and (s.kind in {skVar, skResult} or (s.kind == skParam and isOutParam(s.typ))) and
proc isLocalSym(a: PEffects, s: PSym): bool =
s.typ != nil and (s.kind in {skLet, skVar, skResult} or (s.kind == skParam and isOutParam(s.typ))) and
sfGlobal notin s.flags and s.owner == a.owner
proc lockLocations(a: PEffects; pragma: PNode) =
@ -173,10 +177,15 @@ proc initVar(a: PEffects, n: PNode; volatileCheck: bool) =
let n = skipHiddenDeref(n)
if n.kind != nkSym: return
let s = n.sym
if isLocalVar(a, s):
if isLocalSym(a, s):
if volatileCheck: makeVolatile(a, s)
for x in a.init:
if x == s.id: return
if x == s.id:
if strictDefs in a.c.features and s.kind == skLet:
localError(a.config, n.info, errXCannotBeAssignedTo %
renderTree(n, {renderNoComments}
))
return
a.init.add s.id
if a.scopes.getOrDefault(s.id) == a.currentBlock:
#[ Consider this case:
@ -204,7 +213,7 @@ proc initVarViaNew(a: PEffects, n: PNode) =
# 'x' is not nil, but that doesn't mean its "not nil" children
# are initialized:
initVar(a, n, volatileCheck=true)
elif isLocalVar(a, s):
elif isLocalSym(a, s):
makeVolatile(a, s)
proc warnAboutGcUnsafe(n: PNode; conf: ConfigRef) =
@ -322,7 +331,7 @@ proc useVar(a: PEffects, n: PNode) =
let s = n.sym
if a.inExceptOrFinallyStmt > 0:
incl s.flags, sfUsedInFinallyOrExcept
if isLocalVar(a, s):
if isLocalSym(a, s):
if sfNoInit in s.flags:
# If the variable is explicitly marked as .noinit. do not emit any error
a.init.add s.id
@ -331,7 +340,10 @@ proc useVar(a: PEffects, n: PNode) =
message(a.config, n.info, warnProveInit, s.name.s)
elif a.leftPartOfAsgn <= 0:
if strictDefs in a.c.features:
message(a.config, n.info, warnUninit, s.name.s)
if s.kind == skLet:
localError(a.config, n.info, errLetNeedsInit)
else:
message(a.config, n.info, warnUninit, s.name.s)
# prevent superfluous warnings about the same variable:
a.init.add s.id
useVarNoInitCheck(a, n, s)
@ -637,7 +649,7 @@ proc trackOperandForIndirectCall(tracked: PEffects, n: PNode, formals: PType; ar
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):
if n.kind == nkSym and isLocalSym(tracked, n.sym):
makeVolatile(tracked, n.sym)
if paramType != nil and paramType.kind == tyProc and tfGcSafe in paramType.flags:
let argtype = skipTypes(a.typ, abstractInst)
@ -1025,7 +1037,7 @@ proc track(tracked: PEffects, n: PNode) =
# bug #15038: ensure consistency
if not hasDestructor(n.typ) and sameType(n.typ, n.sym.typ): n.typ = n.sym.typ
of nkHiddenAddr, nkAddr:
if n[0].kind == nkSym and isLocalVar(tracked, n[0].sym):
if n[0].kind == nkSym and isLocalSym(tracked, n[0].sym):
useVarNoInitCheck(tracked, n[0], n[0].sym)
else:
track(tracked, n[0])
@ -1065,7 +1077,7 @@ proc track(tracked: PEffects, n: PNode) =
when false: cstringCheck(tracked, n)
if tracked.owner.kind != skMacro and n[0].typ.kind notin {tyOpenArray, tyVarargs}:
createTypeBoundOps(tracked, n[0].typ, n.info)
if n[0].kind != nkSym or not isLocalVar(tracked, n[0].sym):
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