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Handle assertion error in TyperState #23665

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Merged
merged 1 commit into from
Aug 5, 2025
Merged

Handle assertion error in TyperState #23665

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10 changes: 7 additions & 3 deletions compiler/src/dotty/tools/dotc/core/TyperState.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,8 @@ object TyperState {

opaque type Snapshot = (Constraint, TypeVars, LevelMap)

class BadTyperStateAssertion(msg: String) extends AssertionError(msg)

extension (ts: TyperState)
def snapshot()(using Context): Snapshot =
(ts.constraint, ts.ownedVars, ts.upLevels)
Expand All @@ -43,7 +45,7 @@ object TyperState {
}

class TyperState() {
import TyperState.LevelMap
import TyperState.{LevelMap, BadTyperStateAssertion}

private var myId: Int = uninitialized
def id: Int = myId
Expand Down Expand Up @@ -269,8 +271,10 @@ class TyperState() {
*/
private def includeVar(tvar: TypeVar)(using Context): Unit =
val oldState = tvar.owningState.nn.get
assert(oldState == null || !oldState.isCommittable,
i"$this attempted to take ownership of $tvar which is already owned by committable $oldState")

if oldState != null && oldState.isCommittable then
throw BadTyperStateAssertion(
i"$this attempted to take ownership of $tvar which is already owned by committable $oldState")
tvar.owningState = new WeakReference(this)
ownedVars += tvar

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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/typer/Migrations.scala
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Expand Up @@ -162,6 +162,7 @@ trait Migrations:
private def checkParentheses(tree: Tree, pt: FunProto)(using Context): Boolean =
val ptSpan = pt.args.head.span
ptSpan.exists
&& tree.span.exists
&& ctx.source.content
.slice(tree.span.end, ptSpan.start)
.exists(_ == '(')
Expand Down
13 changes: 11 additions & 2 deletions compiler/src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -4368,11 +4368,20 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
|| !isFullyDefined(formal, ForceDegree.none)
// more context might constrain type variables which could make implicit scope larger

// Try to constrain the result using `pt1`, but back out if a BadTyperStateAssertion
// is thrown. TODO Find out why the bad typer state arises and prevent it. The try-catch
// is a temporary hack to keep projects compiling that would fail otherwise due to
// searching more arguments to instantiate implicits (PR #23532). A failing project
// is described in issue #23609.
def tryConstrainResult(pt: Type): Boolean =
try constrainResult(tree.symbol, wtp, pt)
catch case ex: TyperState.BadTyperStateAssertion => false

arg.tpe match
case failed: SearchFailureType if canProfitFromMoreConstraints =>
val pt1 = pt.deepenProtoTrans
if (pt1 `ne` pt) && (pt1 ne sharpenedPt) && constrainResult(tree.symbol, wtp, pt1)
then return implicitArgs(formals, argIndex, pt1)
if (pt1 `ne` pt) && (pt1 ne sharpenedPt) && tryConstrainResult(pt1) then
return implicitArgs(formals, argIndex, pt1)
case _ =>

arg.tpe match
Expand Down
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