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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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27
compiler/semexprs.nim
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@ -736,7 +736,7 @@ proc hasUnresolvedArgs(c: PContext, n: PNode): bool =
if hasUnresolvedArgs(c, n[i]): return true
return false
proc newHiddenAddrTaken(c: PContext, n: PNode): PNode =
proc newHiddenAddrTaken(c: PContext, n: PNode, isOutParam: bool): PNode =
if n.kind == nkHiddenDeref and not (c.config.backend == backendCpp or
sfCompileToCpp in c.module.flags):
checkSonsLen(n, 1, c.config)
@ -745,13 +745,17 @@ proc newHiddenAddrTaken(c: PContext, n: PNode): PNode =
result = newNodeIT(nkHiddenAddr, n.info, makeVarType(c, n.typ))
result.add n
let aa = isAssignable(c, n)
let sym = getRoot(n)
if aa notin {arLValue, arLocalLValue}:
if aa == arDiscriminant and c.inUncheckedAssignSection > 0:
discard "allow access within a cast(unsafeAssign) section"
elif strictDefs in c.features and aa == arAddressableConst and
sym != nil and sym.kind == skLet and isOutParam:
discard "allow let varaibles to be passed to out parameters"
else:
localError(c.config, n.info, errVarForOutParamNeededX % renderNotLValue(n))
proc analyseIfAddressTaken(c: PContext, n: PNode): PNode =
proc analyseIfAddressTaken(c: PContext, n: PNode, isOutParam: bool): PNode =
result = n
case n.kind
of nkSym:
@ -759,7 +763,7 @@ proc analyseIfAddressTaken(c: PContext, n: PNode): PNode =
if n.sym.typ != nil and
skipTypes(n.sym.typ, abstractInst-{tyTypeDesc}).kind notin {tyVar, tyLent}:
incl(n.sym.flags, sfAddrTaken)
result = newHiddenAddrTaken(c, n)
result = newHiddenAddrTaken(c, n, isOutParam)
of nkDotExpr:
checkSonsLen(n, 2, c.config)
if n[1].kind != nkSym:
@ -767,14 +771,14 @@ proc analyseIfAddressTaken(c: PContext, n: PNode): PNode =
return
if skipTypes(n[1].sym.typ, abstractInst-{tyTypeDesc}).kind notin {tyVar, tyLent}:
incl(n[1].sym.flags, sfAddrTaken)
result = newHiddenAddrTaken(c, n)
result = newHiddenAddrTaken(c, n, isOutParam)
of nkBracketExpr:
checkMinSonsLen(n, 1, c.config)
if skipTypes(n[0].typ, abstractInst-{tyTypeDesc}).kind notin {tyVar, tyLent}:
if n[0].kind == nkSym: incl(n[0].sym.flags, sfAddrTaken)
result = newHiddenAddrTaken(c, n)
result = newHiddenAddrTaken(c, n, isOutParam)
else:
result = newHiddenAddrTaken(c, n)
result = newHiddenAddrTaken(c, n, isOutParam)
proc analyseIfAddressTakenInCall(c: PContext, n: PNode) =
checkMinSonsLen(n, 1, c.config)
@ -820,7 +824,7 @@ proc analyseIfAddressTakenInCall(c: PContext, n: PNode) =
if i < t.len and
skipTypes(t[i], abstractInst-{tyTypeDesc}).kind in {tyVar}:
if n[i].kind != nkHiddenAddr:
n[i] = analyseIfAddressTaken(c, n[i])
n[i] = analyseIfAddressTaken(c, n[i], isOutParam(skipTypes(t[i], abstractInst-{tyTypeDesc})))
include semmagic
@ -1812,11 +1816,16 @@ proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
# a = b # both are vars, means: a[] = b[]
# a = b # b no 'var T' means: a = addr(b)
var le = a.typ
let assignable = isAssignable(c, a)
let root = getRoot(a)
let useStrictDefLet = root != nil and root.kind == skLet and
assignable == arAddressableConst and
strictDefs in c.features and isLocalSym(root)
if le == nil:
localError(c.config, a.info, "expression has no type")
elif (skipTypes(le, {tyGenericInst, tyAlias, tySink}).kind notin {tyVar} and
isAssignable(c, a) in {arNone, arLentValue, arAddressableConst}) or (
skipTypes(le, abstractVar).kind in {tyOpenArray, tyVarargs} and views notin c.features):
assignable in {arNone, arLentValue, arAddressableConst} and not useStrictDefLet
) or (skipTypes(le, abstractVar).kind in {tyOpenArray, tyVarargs} and views notin c.features):
# Direct assignment to a discriminant is allowed!
localError(c.config, a.info, errXCannotBeAssignedTo %
renderTree(a, {renderNoComments}))