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better support for view types (#15436)

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* you can put borrows into tables

* enforces mutating views only mutate mutable data
This commit is contained in:
Andreas Rumpf 2020-09-30 20:44:18 +02:00 • committed by GitHub
commit 86d7b63e2a
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5 changed files with 139 additions and 11 deletions
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54
compiler/varpartitions.nim
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@ -54,7 +54,9 @@ type
VarFlag = enum
ownsData,
preventCursor,
isReassigned
isReassigned,
viewDoesMutate,
viewBorrowsFromConst
VarIndexKind = enum
isEmptyRoot,
@ -478,9 +480,12 @@ proc pretendOwnsData(c: var Partitions, s: PSym) =
const
explainCursors = false
proc isConstSym(s: PSym): bool =
result = s.kind in {skConst, skLet} or isConstParam(s)
proc borrowFrom(c: var Partitions; dest: PSym; src: PNode) =
const
url = "; see https://nim-lang.github.io/Nim/manual_experimental.html#view-types-algorithm-path-expressions for details"
url = "see https://nim-lang.github.io/Nim/manual_experimental.html#view-types-algorithm-path-expressions for details"
let s = pathExpr(src, c.owner)
if s == nil:
@ -499,28 +504,50 @@ proc borrowFrom(c: var Partitions; dest: PSym; src: PNode) =
aliveStart: MinTime, aliveEnd: MaxTime)
c.s[vid].borrowsFrom.add sourceIdx
if isConstSym(s.sym):
c.s[vid].flags.incl viewBorrowsFromConst
else:
discard "a valid borrow location that is a deeply constant expression so we have nothing to track"
let vid = variableId(c, dest)
if vid >= 0:
c.s[vid].flags.incl viewBorrowsFromConst
#discard "a valid borrow location that is a deeply constant expression so we have nothing to track"
proc borrowingCall(c: var Partitions; destType: PType; n: PNode; i: int) =
let v = pathExpr(n[i], c.owner)
if v.kind == nkSym:
if v != nil and v.kind == nkSym:
when false:
let isView = directViewType(destType) == immutableView
if n[0].kind == nkSym and n[0].sym.name.s == "[]=":
localError(c.config, n[i].info, "attempt to mutate an immutable view")
for j in i+1..<n.len:
if getMagic(n[j]) == mSlice:
borrowFrom(c, v.sym, n[j])
else:
localError(c.config, n[i].info, "cannot determine the target of the borrow")
proc trackBorrow(c: var Partitions; dest, src: PNode) =
proc borrowingAsgn(c: var Partitions; dest, src: PNode) =
if dest.kind == nkSym:
let vk = directViewType(dest.typ)
if vk != noView:
if directViewType(dest.typ) != noView:
borrowFrom(c, dest.sym, src)
elif dest.kind in {nkHiddenDeref, nkDerefExpr, nkBracketExpr}:
case directViewType(dest[0].typ)
of mutableView:
# we do not borrow, but we use the view to mutate the borrowed
# location:
let viewOrigin = pathExpr(dest, c.owner)
if viewOrigin.kind == nkSym:
let vid = variableId(c, viewOrigin.sym)
if vid >= 0:
c.s[vid].flags.incl viewDoesMutate
of immutableView:
localError(c.config, dest.info, "attempt to mutate a borrowed location from an immutable view")
of noView: discard "nothing to do"
proc deps(c: var Partitions; dest, src: PNode) =
if not c.performCursorInference:
trackBorrow(c, dest, src)
borrowingAsgn(c, dest, src)
var targets, sources: seq[PSym]
allRoots(dest, targets)
@ -801,6 +828,7 @@ proc checkBorrowedLocations*(par: var Partitions; body: PNode; config: ConfigRef
if v.kind != skParam and classifyViewType(v.typ) != noView:
let rid = root(par, i)
if rid >= 0:
var constViolation = false
for b in par.s[rid].borrowsFrom:
let sid = root(par, b)
if sid >= 0:
@ -809,6 +837,16 @@ proc checkBorrowedLocations*(par: var Partitions; body: PNode; config: ConfigRef
if par.s[sid].sym.kind != skParam and par.s[sid].aliveEnd < par.s[rid].aliveEnd:
localError(config, v.info, "'" & v.name.s & "' borrows from location '" & par.s[sid].sym.name.s &
"' which does not live long enough")
if viewDoesMutate in par.s[rid].flags and isConstSym(par.s[sid].sym):
localError(config, v.info, "'" & v.name.s & "' borrows from the immutable location '" &
par.s[sid].sym.name.s & "' and attempts to mutate it")
constViolation = true
if {viewDoesMutate, viewBorrowsFromConst} * par.s[rid].flags == {viewDoesMutate, viewBorrowsFromConst} and
not constViolation:
# we do not track the constant expressions we allow to borrow from so
# we can only produce a more generic error message:
localError(config, v.info, "'" & v.name.s &
"' borrows from an immutable location and attempts to mutate it")
#if par.s[rid].con.kind == isRootOf and dangerousMutation(par.graphs[par.s[rid].con.graphIndex], par.s[i]):
# cannotBorrow(config, s, par.graphs[par.s[rid].con.graphIndex])