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wasm generation bug workaround, docs and debugging tips

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This commit is contained in:
Sergey Chernov 2026-01-24 18:10:49 +03:00
parent 7b1ba71ef0
commit 717a79aca2
5 changed files with 514 additions and 788 deletions
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15
docs/ai_notes_wasm_generation_bug.md Normal file
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@ -0,0 +1,15 @@
# AI notes: avoid Kotlin/Wasm invalid IR with suspend lambdas
## Do
- Prefer explicit `object : Statement()` with `override suspend fun execute(...)` when building compiler statements.
- Keep `Statement` objects non-lambda, especially in compiler hot paths like parsing/var declarations.
- If you need conditional behavior, return early in `execute` instead of wrapping `parseExpression()` with `statement(...) { ... }`.
- When wasmJs tests hang in the browser, first check `wasmJsNodeTest` for a compile error; hangs often mean module instantiation failed.
## Don't
- Do not create suspend lambdas inside `Statement` factories (`statement { ... }`) for wasm targets.
- Do not "fix" hangs by increasing browser timeouts; it masks invalid wasm generation.
## Debugging tips
- Look for `$invokeCOROUTINE$` in wasm function names when mapping failures.
- If node test logs a wasm compile error, the browser hang is likely the same root cause.

27
docs/wasm_generation_bug.md Normal file
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@ -0,0 +1,27 @@
# Wasm generation hang in wasmJs browser tests
## Summary
The wasmJs browser test runner hung after commit 5f819dc. The root cause was invalid WebAssembly generated by the Kotlin/Wasm backend when certain compiler paths emitted suspend lambdas for `Statement` execution. The invalid module failed to instantiate in the browser, and Karma kept the browser connected but never ran tests.
## Symptoms
- `:lynglib:wasmJsBrowserTest` hangs indefinitely in ChromeHeadless.
- `:lynglib:wasmJsNodeTest` fails with a WebAssembly compile error similar to:
- `struct.set expected type (ref null XXXX), found global.get of type (ref null YYYY)`
- The failing function name in the wasm name section looks like:
- `net.sergeych.lyng.$invokeCOROUTINE$.doResume`
## Root cause
The delegation/var-declaration changes introduced compiler-generated suspend lambdas inside `Statement` construction (e.g., `statement { ... }` wrappers). Kotlin/Wasm generates extra coroutine state for those suspend lambdas, which in this case produced invalid wasm IR (mismatched GC reference types). The browser loader then waits forever because the module fails to instantiate.
## Fix
Avoid suspend-lambda `Statement` construction in compiler code paths. Replace `statement { ... }` and other anonymous suspend lambdas with explicit `object : Statement()` implementations and move logic into `override suspend fun execute(...)`. This keeps the resulting wasm IR valid while preserving behavior.
## Where it was fixed
- `lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt`
- `lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt`
## Verification
- `./gradlew :lynglib:wasmJsNodeTest --info`
- `./gradlew :lynglib:wasmJsBrowserTest --info`
Both tests finish quickly after the change.

796
lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt
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189
lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt
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@ -70,8 +70,9 @@ open class Scope(
internal fun findExtension(receiverClass: ObjClass, name: String): ObjRecord? {
var s: Scope? = this
var hops = 0
while (s != null && hops++ < 1024) {
val visited = HashSet<Long>(4)
while (s != null) {
if (!visited.add(s.frameId)) break
// Proximity rule: check all extensions in the current scope before going to parent.
// Priority within scope: more specific class in MRO wins.
for (cls in receiverClass.mro) {
@ -105,38 +106,28 @@ open class Scope(
* intertwined closure frames. They traverse the plain parent chain and consult only locals
* and bindings of each frame. Instance/class member fallback must be decided by the caller.
*/
internal fun tryGetLocalRecord(s: Scope, name: String, caller: net.sergeych.lyng.obj.ObjClass?): ObjRecord? {
caller?.let { ctx ->
s.objects[ctx.mangledName(name)]?.let { rec ->
if (rec.visibility == Visibility.Private) return rec
}
}
private fun tryGetLocalRecord(s: Scope, name: String, caller: net.sergeych.lyng.obj.ObjClass?): ObjRecord? {
s.objects[name]?.let { rec ->
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller, name)) return rec
}
caller?.let { ctx ->
s.localBindings[ctx.mangledName(name)]?.let { rec ->
if (rec.visibility == Visibility.Private) return rec
}
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller)) return rec
}
s.localBindings[name]?.let { rec ->
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller, name)) return rec
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller)) return rec
}
s.getSlotIndexOf(name)?.let { idx ->
val rec = s.getSlotRecord(idx)
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller, name)) return rec
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, caller)) return rec
}
return null
}
internal fun chainLookupIgnoreClosure(name: String, followClosure: Boolean = false, caller: net.sergeych.lyng.obj.ObjClass? = null): ObjRecord? {
internal fun chainLookupIgnoreClosure(name: String): ObjRecord? {
var s: Scope? = this
// use hop counter to detect unexpected structural cycles in the parent chain
var hops = 0
val effectiveCaller = caller ?: currentClassCtx
while (s != null && hops++ < 1024) {
tryGetLocalRecord(s, name, effectiveCaller)?.let { return it }
s = if (followClosure && s is ClosureScope) s.closureScope else s.parent
// use frameId to detect unexpected structural cycles in the parent chain
val visited = HashSet<Long>(4)
while (s != null) {
if (!visited.add(s.frameId)) return null
tryGetLocalRecord(s, name, currentClassCtx)?.let { return it }
s = s.parent
}
return null
}
@ -153,8 +144,9 @@ open class Scope(
tryGetLocalRecord(this, name, currentClassCtx)?.let { return it }
// 2) walk parents for plain locals/bindings only
var s = parent
var hops = 0
while (s != null && hops++ < 1024) {
val visited = HashSet<Long>(4)
while (s != null) {
if (!visited.add(s.frameId)) return null
tryGetLocalRecord(s, name, currentClassCtx)?.let { return it }
s = s.parent
}
@ -163,7 +155,7 @@ open class Scope(
this.extensions[cls]?.get(name)?.let { return it }
}
return thisObj.objClass.getInstanceMemberOrNull(name)?.let { rec ->
if (canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx, name)) {
if (canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx)) {
if (rec.type == ObjRecord.Type.Field || rec.type == ObjRecord.Type.Property || rec.isAbstract) null
else rec
} else null
@ -177,22 +169,23 @@ open class Scope(
* This completely avoids invoking overridden `get` implementations, preventing
* ping-pong recursion between `ClosureScope` frames.
*/
internal fun chainLookupWithMembers(name: String, caller: net.sergeych.lyng.obj.ObjClass? = currentClassCtx, followClosure: Boolean = false): ObjRecord? {
internal fun chainLookupWithMembers(name: String, caller: net.sergeych.lyng.obj.ObjClass? = currentClassCtx): ObjRecord? {
var s: Scope? = this
var hops = 0
while (s != null && hops++ < 1024) {
val visited = HashSet<Long>(4)
while (s != null) {
if (!visited.add(s.frameId)) return null
tryGetLocalRecord(s, name, caller)?.let { return it }
for (cls in s.thisObj.objClass.mro) {
s.extensions[cls]?.get(name)?.let { return it }
}
s.thisObj.objClass.getInstanceMemberOrNull(name)?.let { rec ->
if (canAccessMember(rec.visibility, rec.declaringClass, caller, name)) {
if (canAccessMember(rec.visibility, rec.declaringClass, caller)) {
if (rec.type == ObjRecord.Type.Field || rec.type == ObjRecord.Type.Property || rec.isAbstract) {
// ignore fields, properties and abstracts here, they will be handled by the caller via readField
} else return rec
}
}
s = if (followClosure && s is ClosureScope) s.closureScope else s.parent
s = s.parent
}
return null
}
@ -284,22 +277,16 @@ open class Scope(
raiseError(ObjSymbolNotDefinedException(this, "symbol is not defined: $name"))
fun raiseError(message: String): Nothing {
val ex = ObjException(this, message)
throw ExecutionError(ex, pos, ex.message.value)
throw ExecutionError(ObjException(this, message))
}
fun raiseError(obj: ObjException): Nothing {
throw ExecutionError(obj, obj.scope.pos, obj.message.value)
}
fun raiseError(obj: Obj, pos: Pos, message: String): Nothing {
throw ExecutionError(obj, pos, message)
throw ExecutionError(obj)
}
@Suppress("unused")
fun raiseNotFound(message: String = "not found"): Nothing {
val ex = ObjNotFoundException(this, message)
throw ExecutionError(ex, ex.scope.pos, ex.message.value)
throw ExecutionError(ObjNotFoundException(this, message))
}
inline fun <reified T : Obj> requiredArg(index: Int): T {
@ -327,51 +314,37 @@ open class Scope(
inline fun <reified T : Obj> thisAs(): T {
var s: Scope? = this
while (s != null) {
val t = s.thisObj
do {
val t = s!!.thisObj
if (t is T) return t
s = s.parent
}
} while (s != null)
raiseClassCastError("Cannot cast ${thisObj.objClass.className} to ${T::class.simpleName}")
}
internal val objects = mutableMapOf<String, ObjRecord>()
open operator fun get(name: String): ObjRecord? {
if (name == "this") return thisObj.asReadonly
// 1. Prefer direct locals/bindings declared in this frame
tryGetLocalRecord(this, name, currentClassCtx)?.let { return it }
val p = parent
// 2. If we share thisObj with parent, delegate to parent to maintain
// "locals shadow members" priority across the this-context.
if (p != null && p.thisObj === thisObj) {
return p.get(name)
open operator fun get(name: String): ObjRecord? =
if (name == "this") thisObj.asReadonly
else {
// Prefer direct locals/bindings declared in this frame
(objects[name]?.let { rec ->
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx)) rec else null
}
// 3. Otherwise, we are the "primary" scope for this thisObj (or have no parent),
// so check members of thisObj before walking up to a different this-context.
val receiver = thisObj
val effectiveClass = receiver as? ObjClass ?: receiver.objClass
for (cls in effectiveClass.mro) {
val rec = cls.members[name] ?: cls.classScope?.objects?.get(name)
if (rec != null && !rec.isAbstract) {
if (canAccessMember(rec.visibility, rec.declaringClass ?: cls, currentClassCtx, name)) {
return rec.copy(receiver = receiver)
// Then, check known local bindings in this frame (helps after suspension)
?: localBindings[name]?.let { rec ->
if (rec.declaringClass == null || canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx)) rec else null
}
// Walk up ancestry
?: parent?.get(name)
// Finally, fallback to class members on thisObj
?: thisObj.objClass.getInstanceMemberOrNull(name)?.let { rec ->
if (canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx)) {
if (rec.type == ObjRecord.Type.Field || rec.type == ObjRecord.Type.Property || rec.isAbstract) null
else rec
} else null
}
}
// Finally, root object fallback
Obj.rootObjectType.members[name]?.let { rec ->
if (canAccessMember(rec.visibility, rec.declaringClass, currentClassCtx, name)) {
return rec.copy(receiver = receiver)
}
}
// 4. Finally, walk up ancestry to a scope with a different thisObj context
return p?.get(name)
)
}
// Slot fast-path API
@ -392,20 +365,6 @@ open class Scope(
nameToSlot[name]?.let { slots[it] = record }
}
/**
* Clear all references and maps to prevent memory leaks when pooled.
*/
fun scrub() {
this.parent = null
this.skipScopeCreation = false
this.currentClassCtx = null
objects.clear()
slots.clear()
nameToSlot.clear()
localBindings.clear()
extensions.clear()
}
/**
* Reset this scope instance so it can be safely reused as a fresh child frame.
* Clears locals and slots, assigns new frameId, and sets parent/args/pos/thisObj.
@ -415,7 +374,6 @@ open class Scope(
// that could interact badly with the new parent and produce a cycle.
this.parent = null
this.skipScopeCreation = false
this.currentClassCtx = parent?.currentClassCtx
// fresh identity for PIC caches
this.frameId = nextFrameId()
// clear locals and slot maps
@ -516,8 +474,7 @@ open class Scope(
declaringClass: net.sergeych.lyng.obj.ObjClass? = currentClassCtx,
isAbstract: Boolean = false,
isClosed: Boolean = false,
isOverride: Boolean = false,
isTransient: Boolean = false
isOverride: Boolean = false
): ObjRecord {
val rec = ObjRecord(
value, isMutable, visibility, writeVisibility,
@ -525,8 +482,7 @@ open class Scope(
type = recordType,
isAbstract = isAbstract,
isClosed = isClosed,
isOverride = isOverride,
isTransient = isTransient
isOverride = isOverride
)
objects[name] = rec
// Index this binding within the current frame to help resolve locals across suspension
@ -545,16 +501,12 @@ open class Scope(
}
}
// Map to a slot for fast local access (ensure consistency)
if (nameToSlot.isEmpty()) {
allocateSlotFor(name, rec)
} else {
val idx = nameToSlot[name]
val idx = getSlotIndexOf(name)
if (idx == null) {
allocateSlotFor(name, rec)
} else {
slots[idx] = rec
}
}
return rec
}
@ -670,34 +622,31 @@ open class Scope(
}
suspend fun resolve(rec: ObjRecord, name: String): Obj {
val receiver = rec.receiver ?: thisObj
return receiver.resolveRecord(this, rec, name, rec.declaringClass).value
if (rec.type == ObjRecord.Type.Delegated) {
val del = rec.delegate ?: raiseError("Internal error: delegated property $name has no delegate")
val th = if (thisObj === ObjVoid) ObjNull else thisObj
if (del.objClass.getInstanceMemberOrNull("getValue") == null) {
return object : Statement() {
override val pos: Pos = Pos.builtIn
override suspend fun execute(scope: Scope): Obj {
val th2 = if (scope.thisObj === ObjVoid) ObjNull else scope.thisObj
val allArgs = (listOf(th2, ObjString(name)) + scope.args.list).toTypedArray()
return del.invokeInstanceMethod(scope, "invoke", Arguments(*allArgs))
}
}
}
return del.invokeInstanceMethod(this, "getValue", Arguments(th, ObjString(name)))
}
return rec.value
}
suspend fun assign(rec: ObjRecord, name: String, newValue: Obj) {
if (rec.type == ObjRecord.Type.Delegated) {
val receiver = rec.receiver ?: thisObj
val del = rec.delegate ?: run {
if (receiver is ObjInstance) {
(receiver as ObjInstance).writeField(this, name, newValue)
return
}
raiseError("Internal error: delegated property $name has no delegate")
}
val th = if (receiver === ObjVoid) ObjNull else receiver
val del = rec.delegate ?: raiseError("Internal error: delegated property $name has no delegate")
val th = if (thisObj === ObjVoid) ObjNull else thisObj
del.invokeInstanceMethod(this, "setValue", Arguments(th, ObjString(name), newValue))
return
}
if (rec.value is ObjProperty) {
(rec.value as ObjProperty).callSetter(this, rec.receiver ?: thisObj, newValue, rec.declaringClass)
return
}
// If it's a member (explicitly tracked by receiver or declaringClass), use writeField.
// Important: locals have receiver == null and declaringClass == null (enforced in addItem).
if (rec.receiver != null || (rec.declaringClass != null && (rec.type == ObjRecord.Type.Field || rec.type == ObjRecord.Type.Property))) {
(rec.receiver ?: thisObj).writeField(this, name, newValue)
return
}
if (!rec.isMutable && rec.value !== ObjUnset) raiseIllegalAssignment("can't reassign val $name")
rec.value = newValue
}

27
lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt
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@ -501,9 +501,8 @@ open class Obj {
if (obj.type == ObjRecord.Type.Delegated) {
val del = obj.delegate ?: scope.raiseError("Internal error: delegated property $name has no delegate")
val th = if (this === ObjVoid) ObjNull else this
val res = del.invokeInstanceMethod(scope, "getValue", Arguments(th, ObjString(name)), onNotFoundResult = {
// If getValue not found, return a wrapper that calls invoke
object : Statement() {
if (del.objClass.getInstanceMemberOrNull("getValue") == null) {
val wrapper = object : Statement() {
override val pos: Pos = Pos.builtIn
override suspend fun execute(s: Scope): Obj {
val th2 = if (s.thisObj === ObjVoid) ObjNull else s.thisObj
@ -511,7 +510,12 @@ open class Obj {
return del.invokeInstanceMethod(s, "invoke", Arguments(*allArgs))
}
}
})
return obj.copy(
value = wrapper,
type = ObjRecord.Type.Other
)
}
val res = del.invokeInstanceMethod(scope, "getValue", Arguments(th, ObjString(name)))
return obj.copy(
value = res,
type = ObjRecord.Type.Other
@ -605,16 +609,17 @@ open class Obj {
scope.raiseNotImplemented()
}
suspend fun invoke(scope: Scope, thisObj: Obj, args: Arguments, declaringClass: ObjClass? = null): Obj =
if (PerfFlags.SCOPE_POOL)
scope.withChildFrame(args, newThisObj = thisObj) { child ->
suspend fun invoke(scope: Scope, thisObj: Obj, args: Arguments, declaringClass: ObjClass? = null): Obj {
if (PerfFlags.SCOPE_POOL) {
return scope.withChildFrame(args, newThisObj = thisObj) { child ->
if (declaringClass != null) child.currentClassCtx = declaringClass
callOn(child)
}
else
callOn(scope.createChildScope(scope.pos, args = args, newThisObj = thisObj).also {
if (declaringClass != null) it.currentClassCtx = declaringClass
})
}
val child = scope.createChildScope(scope.pos, args = args, newThisObj = thisObj)
if (declaringClass != null) child.currentClassCtx = declaringClass
return callOn(child)
}
suspend fun invoke(scope: Scope, thisObj: Obj, vararg args: Obj): Obj =
callOn(