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demotomohirodemotomohiro
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Port derefs.nim in Nimony to Nim 2 #25183; Borrow / Mutability checks
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‎compiler/sem.nim‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -18,7 +18,7 @@ import
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evaltempl, patterns, parampatterns, sempass2, linter, semmacrosanity,
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lowerings, plugins/active, lineinfos, int128,
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isolation_check, typeallowed, modulegraphs, enumtostr, concepts, astmsgs,
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extccomp, layeredtable
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extccomp, layeredtable, semderefs
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import vtables
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import std/[strtabs, math, tables, intsets, strutils, packedsets]
@@ -821,6 +821,7 @@ proc semStmtAndGenerateGenerics(c: PContext, n: PNode): PNode =
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else:
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result = n
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result = semStmt(c, result, {})
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result = injectDerefs(c.config, result)
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when false:
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# Code generators are lazy now and can deal with undeclared procs, so these
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# steps are not required anymore and actually harmful for the upcoming

‎compiler/semderefs.nim‎

Lines changed: 217 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,217 @@
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import ast, lineinfos, msgs, options, renderer
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import std/[strutils]
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type
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Expects = enum
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WantT
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WantTButSkipDeref
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WantVarT
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WantVarTResult
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WantMutableT # `var openArray` does need derefs but mutable locations regardless
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WantForwarding
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CurrentRoutine = object
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returnExpects: Expects
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firstParamKind: TTypeKind
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firstParam: PSym
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resultSym: PSym
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routineSym: PSym
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Context = object
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config: ConfigRef
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r: CurrentRoutine
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proc tr(c: var Context; n: PNode; e: Expects): PNode
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proc trSons(c: var Context; n: PNode; e: Expects): PNode =
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for i in 0 ..< n.safeLen:
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n[i] = tr(c, n[i], e)
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result = n
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proc validBorrowsFrom(c: var Context; n: PNode): bool =
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# --------------------------------------------------------------------------
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# We need to borrow from a location that is derived from the proc's
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# first parameter.
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# See RFC #7373
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# --------------------------------------------------------------------------
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result = false
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var n = n
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var someIndirection = false
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while true:
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case n.kind
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of nkDotExpr, nkCheckedFieldExpr, nkBracketExpr, nkObjUpConv, nkObjDownConv:
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n = n[0]
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of nkHiddenStdConv, nkHiddenSubConv, nkConv:
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n = n[1]
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of nkHiddenDeref, nkHiddenAddr, nkDerefExpr, nkAddr:
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n = n[0]
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someIndirection = true
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of nkStmtList, nkStmtListExpr:
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if n.len > 0 and n.typ != nil: n = n.lastSon
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else: break
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of nkCallKinds:
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if n.len > 1:
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let fnType = n[0].typ
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n = n[1]
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if fnType != nil and fnType.len > 1:
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let firstParamType = fnType[1]
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let mightForward = firstParamType.kind in {tyVar, tyLent}
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if not mightForward:
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someIndirection = true
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else:
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break
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else:
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break
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if n.kind == nkSym:
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if n.sym.kind == skParam and n.sym == c.r.firstParam:
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result = c.r.firstParamKind in {tyVar, tyLent} or someIndirection
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else:
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# Allow borrow from global or captured variables for backwards compatibility.
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result = n.sym.owner != c.r.routineSym
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else:
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result = false
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proc skipToRoot(n: PNode): PNode =
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var n = n
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while true:
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case n.kind
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of nkDotExpr, nkCheckedFieldExpr, nkBracketExpr, nkObjUpConv, nkObjDownConv:
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n = n[0]
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of nkHiddenStdConv, nkHiddenSubConv, nkConv, nkCast:
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n = n[1]
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of nkCallKinds:
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if n.len > 1:
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n = n[1]
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else:
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break
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else:
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break
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result = n
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proc borrowsFromReadonly(c: var Context; n: PNode; allowLet = false): bool =
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let n = skipToRoot(n)
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if n.kind == nkSym:
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let tk = n.sym.typ.kind
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case n.sym.kind:
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of skConst:
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result = true
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of skLet:
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if allowLet:
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result = tk == tyLent
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else:
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result = tk notin {tyVar, tyLent}
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of skVar:
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result = tk == tyLent
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of skParam:
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result = tk notin {tyVar, tyLent, tySink}
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else:
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result = false
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elif n.kind in nkLiterals + {nkObjConstr}:
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result = true
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else:
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result = false
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proc wantMutable(e: Expects): bool {.inline.} =
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e in {WantVarT, WantVarTResult, WantMutableT}
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proc trProcDecl(c: var Context; n: PNode): PNode =
120+
if isGenericRoutine(n):
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result = n
122+
else:
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var r = CurrentRoutine(returnExpects: WantT)
124+
if n[namePos].kind == nkSym:
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r.routineSym = n[namePos].sym
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if n[namePos].sym.typ != nil:
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let fnType = n[namePos].sym.typ
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if fnType.len > 1:
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r.firstParamKind = fnType[1].kind
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if n[paramsPos].safeLen > 1 and n[paramsPos][1].kind == nkIdentDefs:
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let firstParam = n[paramsPos][1]
132+
if firstParam[0].kind == nkSym:
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r.firstParam = firstParam[0].sym
134+
if n.len > resultPos and n[resultPos].kind == nkSym:
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r.resultSym = n[resultPos].sym
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if n[resultPos].sym.typ != nil and n[resultPos].sym.typ.kind in {tyVar, tyLent}:
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r.returnExpects = WantVarTResult
138+
139+
swap c.r, r
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result = n
141+
result[bodyPos] = tr(c, n[bodyPos], c.r.returnExpects)
142+
swap c.r, r
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proc cannotPassToVar(c: var Context; info: TLineInfo; arg: PNode) =
145+
localError(c.config, info, "cannot pass '$1' to var/out T parameter" % [renderTree(arg, {renderNoComments})])
146+
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type
148+
LvalueStatus = enum
149+
Valid
150+
InvalidBorrow
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LocationIsConst
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153+
proc trAsgn(c: var Context; n: PNode): PNode =
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var e = WantT
155+
var err = Valid
156+
if n[0].kind == nkSym and n[0].sym.kind == skResult and n[0].sym == c.r.resultSym:
157+
if c.r.returnExpects == WantVarTResult:
158+
if not validBorrowsFrom(c, n[1]):
159+
err = InvalidBorrow
160+
discard
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case err:
162+
of InvalidBorrow:
163+
localError c.config, n.info, "cannot borrow from " & renderTree(n[1], {renderNoComments})
164+
else:
165+
result = tr(c, n[1], e)
166+
result = n
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168+
proc trLocation(c: var Context; n: PNode; e: Expects): PNode =
169+
let typ = n.typ
170+
if typ != nil:
171+
let k = typ.kind
172+
if k in {tyVar, tyLent}:
173+
if e.wantMutable:
174+
# Consider `fvar(returnsVar(someLet))`: We must not allow this.
175+
if borrowsFromReadonly(c, n):
176+
cannotPassToVar c, n.info, n
177+
result = n
178+
else:
179+
result = trSons(c, n, WantT)
180+
else:
181+
result = trSons(c, n, WantT)
182+
elif e.wantMutable:
183+
if e == WantVarTResult:
184+
if n.kind == nkSym:
185+
result = n
186+
else:
187+
result = trSons(c, n, WantT)
188+
elif borrowsFromReadonly(c, n):
189+
cannotPassToVar c, n.info, n
190+
result = n
191+
else:
192+
result = trSons(c, n, WantT)
193+
else:
194+
result = trSons(c, n, WantT)
195+
else:
196+
result = n
197+
198+
proc tr(c: var Context; n: PNode; e: Expects): PNode =
199+
case n.kind
200+
of nkSym:
201+
result = trLocation(c, n, e)
202+
of nkLiterals:
203+
if e.wantMutable:
204+
cannotPassToVar c, n.info, n
205+
result = n
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of nkDotExpr, nkCheckedFieldExpr, nkBracketExpr:
207+
result = trLocation(c, n, e)
208+
of nkAsgn:
209+
result = trAsgn(c, n)
210+
of nkProcDef, nkFuncDef, nkMethodDef, nkConverterDef, nkIteratorDef:
211+
result = trProcDecl(c, n)
212+
else:
213+
result = trSons(c, n, e)
214+
215+
proc injectDerefs*(config: ConfigRef; n: PNode): PNode =
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var c = Context(config: config, r: CurrentRoutine())
217+
result = tr(c, n, WantT)

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