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/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.compiler.plugins.kotlin.inference
import java.lang.NumberFormatException
/**
* A part of a [Scheme].
*/
sealed class Item {
internal abstract val isAnonymous: Boolean
internal open val isUnspecified: Boolean get() = false
internal abstract fun toBinding(bindings: Bindings, context: MutableList): Binding
internal abstract fun serializeTo(writer: SchemeStringSerializationWriter)
}
/**
* A bound part of a [Scheme] that is bound to [value].
*/
class Token(val value: String) : Item() {
override val isAnonymous: Boolean get() = false
override fun toBinding(bindings: Bindings, context: MutableList): Binding =
bindings.closed(value)
override fun toString() = value
override fun equals(other: Any?) = other is Token && other.value == value
override fun hashCode(): Int = value.hashCode() * 31
override fun serializeTo(writer: SchemeStringSerializationWriter) { writer.writeToken(value) }
}
/**
* An open part of a [Scheme]. All [Open] items with the same non-negative index should be bound
* together to the same applier. [Open] items with a negative index are considered anonymous and
* are treated as independent.
*/
class Open(val index: Int, override val isUnspecified: Boolean = false) : Item() {
override val isAnonymous: Boolean get() = index < 0
override fun toBinding(bindings: Bindings, context: MutableList): Binding {
if (index < 0) return bindings.open()
while (index >= context.size) {
context.add(bindings.open())
}
return context[index]
}
override fun toString() = if (index < 0) "_" else "$index"
override fun equals(other: Any?) =
other is Open && (other.index == index || (other.index < 0 && index < 0))
override fun hashCode(): Int = if (index < 0) -31 else index * 31
override fun serializeTo(writer: SchemeStringSerializationWriter) { writer.writeNumber(index) }
}
/**
* A [Scheme] declares the applier the type expects and which appliers are expected of the
* lambda parameters of a function or bound callable types of a generic type. The applier can be
* open but all open appliers of the same non-negative index must be bound to the same applier.
*
* All non-composable lambda parameters of a function type are ignored and skipped when producing
* or interpreting a scheme. Also if the result is not a composable lambda the result is `null`.
* This is because inference is only inferring what applier is being used by the `$composer`
* passed as a parameter of a function. Note that a lambda that captures a `$composer` in context
* (such as the lambda passed to [forEach] in a composable function) has a scheme as if the
* `$composer` captured was passed in as a parameter just like it was a composable lambda.
*/
class Scheme(
val target: Item,
val parameters: List = emptyList(),
val result: Scheme? = null,
val anyParameters: Boolean = false
) {
init {
check(!anyParameters || parameters.isEmpty()) {
"`anyParameters` == true must have empty parameters"
}
}
/**
* Produce a string serialization of the scheme. This is not necessarily readable, use
* [toString] for debugging instead.
*/
fun serialize(): String = buildString { serializeTo(SchemeStringSerializationWriter(this)) }
override fun toString(): String = "[$target$parametersStr$resultStr]"
private val parametersStr get() =
if (parameters.isEmpty()) ""
else ", ${parameters.joinToString(", ") { it.toString() }}"
private val resultStr get() = result?.let { ": $it" } ?: ""
/**
* Compare to [Scheme] instances for equality. Two [Scheme]s are considered equal if they are
* [alpha equivalent][https://en.wikipedia.org/wiki/Lambda_calculus#%CE%B1-conversion]. This
* is accomplished by normalizing both schemes and then comparing them simply for equality.
* See [alphaRename] for details.
*/
override fun equals(other: Any?): Boolean {
val o = other as? Scheme ?: return false
return this.alphaRename().simpleEquals(o.alphaRename())
}
fun canOverride(other: Scheme): Boolean = alphaRename().simpleCanOverride(other.alphaRename())
override fun hashCode(): Int = alphaRename().simpleHashCode()
private fun simpleCanOverride(other: Scheme): Boolean {
return if (other.target is Open) {
target is Open && other.target.index == target.index
} else {
target.isUnspecified || target == other.target
} && parameters.zip(other.parameters).all { (a, b) -> a.simpleCanOverride(b) } &&
(
result == other.result ||
(other.result != null && result != null && result.canOverride((other.result)))
)
}
private fun simpleEquals(other: Scheme) =
target == other.target && parameters.zip(other.parameters).all { (a, b) -> a == b } &&
result == result
private fun simpleHashCode(): Int =
target.hashCode() * 31 + parameters.hashOfElements() + (result?.hashCode() ?: 0)
private fun List.hashOfElements() = if (isEmpty()) 0 else
map { it.simpleHashCode() }.reduceRight { h, acc -> h + acc * 31 }
private fun serializeTo(writer: SchemeStringSerializationWriter) {
writer.writeOpen()
target.serializeTo(writer)
if (anyParameters) {
writer.writeAnyParameters()
} else {
parameters.forEach { it.serializeTo(writer) }
}
if (result != null) {
writer.writeResultPrefix()
result.serializeTo(writer)
}
writer.writeClose()
}
/**
* Both hashCode and equals are in terms of alpha rename equivalents. That means that the scheme
* [0, [0]] and [2, [2]] should be treated as equal even though they have different indexes
* because they are alpha rename equivalent. This method will rename all variables
* consistently so that if they are alpha equivalent then they will have the same open
* indexes in the same location. If the scheme is already alpha rename consistent then this is
* returned.
*/
private fun alphaRename(): Scheme {
// Special case where the scheme would always be renamed to itself.
if ((target !is Open || target.index in -1..0) && parameters.isEmpty()) return this
// Calculate what the renames should be
val alphaRenameMap = mutableMapOf()
var next = 0
fun scan(scheme: Scheme) {
val target = scheme.target
val parameters = scheme.parameters
val result = scheme.result
if (target is Open) {
val index = target.index
if (index in alphaRenameMap) {
if (index >= 0 && alphaRenameMap[index] == -1)
alphaRenameMap[index] = next++
} else alphaRenameMap[index] = -1
}
parameters.forEach { scan(it) }
result?.let { scan(it) }
}
scan(this)
// if no renames found, this is an entirely bound scheme, just return it
if (alphaRenameMap.isEmpty()) return this
fun rename(scheme: Scheme): Scheme {
val target = scheme.target
val parameters = scheme.parameters
val result = scheme.result
val newTarget = if (target is Open && target.index != alphaRenameMap[target.index])
Open(alphaRenameMap[target.index]!!)
else target
val newParameters = parameters.map { rename(it) }
val newResult = result?.let { rename(it) }
return if (
target !== newTarget || newParameters.zip(parameters).any { (a, b) ->
a !== b
} || newResult != result
) Scheme(newTarget, newParameters, newResult)
else scheme
}
return rename(this)
}
}
private class SchemeParseError : Exception("Internal scheme parse error")
private fun schemeParseError(): Nothing { throw SchemeParseError() }
/**
* Given a string produce a [Scheme] if the string is a valid serialization of a [Scheme] or null
* otherwise.
*/
fun deserializeScheme(value: String): Scheme? {
val reader = SchemeStringSerializationReader(value)
fun item(): Item = when (reader.kind) {
ItemKind.Token -> Token(reader.token())
ItemKind.Number -> Open(reader.number())
else -> schemeParseError()
}
fun list(content: () -> T): List {
if (reader.kind != ItemKind.Open) return emptyList()
val result = mutableListOf()
while (reader.kind == ItemKind.Open) {
result.add(content())
}
return result
}
fun delimited(
prefix: ItemKind,
postfix: ItemKind,
content: () -> T
) = run {
reader.expect(prefix)
content().also {
reader.expect(postfix)
}
}
fun optional(
prefix: ItemKind,
postfix: ItemKind = ItemKind.Invalid,
content: () -> T
): T? =
if (reader.kind == prefix) {
delimited(prefix, postfix, content)
} else null
fun isItem(kind: ItemKind): Boolean =
if (reader.kind == kind) {
reader.expect(kind)
true
} else false
fun scheme(): Scheme =
delimited(ItemKind.Open, ItemKind.Close) {
val target = item()
val anyParameters = isItem(ItemKind.AnyParameters)
val parameters = if (anyParameters) emptyList() else list { scheme() }
val result = optional(ItemKind.ResultPrefix) { scheme() }
Scheme(target, parameters, result, anyParameters)
}
return try {
scheme().also { reader.end() }
} catch (_: SchemeParseError) {
null
}
}
internal class SchemeStringSerializationWriter(private val builder: StringBuilder) {
fun writeToken(token: String) {
if (isNormal(token)) {
builder.append(token)
} else {
builder.append('"')
builder.append(token.replace("\\", "\\\\").replace("\"", "\\\""))
builder.append('"')
}
}
fun writeNumber(number: Int) {
if (number < 0) {
builder.append('_')
} else {
builder.append(number)
}
}
fun writeOpen() { builder.append('[') }
fun writeClose() { builder.append(']') }
fun writeResultPrefix() { builder.append(':') }
fun writeAnyParameters() { builder.append('*') }
override fun toString(): String = builder.toString()
private fun isNormal(value: String) = value.all { it == '.' || it.isLetter() }
}
private enum class ItemKind {
Open,
Close,
ResultPrefix,
AnyParameters,
Token,
Number,
End,
Invalid
}
private const val eos = '\u0000'
private class SchemeStringSerializationReader(private val value: String) {
private var current = 0
val kind: ItemKind get() =
when (val ch = ch) {
'_' -> ItemKind.Number
'[' -> ItemKind.Open
']' -> ItemKind.Close
':' -> ItemKind.ResultPrefix
'*' -> ItemKind.AnyParameters
'"' -> ItemKind.Token
else -> {
when {
ch.isLetter() -> ItemKind.Token
ch.isDigit() -> ItemKind.Number
ch == eos -> ItemKind.End
else -> ItemKind.Invalid
}
}
}
fun end() {
if (kind != ItemKind.End)
schemeParseError()
}
fun number(): Int {
if (ch == '_') {
current++
return -1
}
val start = current
while (ch.isDigit())
current++
return try {
Integer.parseUnsignedInt(value, start, current, 10)
} catch (_: NumberFormatException) {
schemeParseError()
}
}
fun token(): String {
var start = current
val end: Int
var prefix = ""
if (ch == '"') {
current++
start = current
while (ch != '"' && ch != eos) {
if (ch == '\\') {
prefix += value.subSequence(start, current).toString()
current++
start = current
if (ch == '\"' || ch == '\\') {
current++
} else {
schemeParseError()
}
} else {
current++
}
}
end = current
current++
} else {
while (run { val ch = ch; ch == '.' || ch.isLetter() }) current++
end = current
}
return prefix + value.subSequence(start, end).toString()
}
fun expect(kind: ItemKind) {
if (kind != ItemKind.Invalid) {
if (this.kind != kind) {
schemeParseError()
}
when (this.kind) {
ItemKind.Open -> expect('[')
ItemKind.Close -> expect(']')
ItemKind.ResultPrefix -> expect(':')
ItemKind.AnyParameters -> expect('*')
ItemKind.Token -> token()
ItemKind.Number -> number()
ItemKind.End -> end()
else -> schemeParseError()
}
}
}
private val ch: Char get() = if (current < value.length) value[current] else eos
private fun expect(ch: Char) {
if (current < value.length && value[current] == ch) {
current++
} else {
schemeParseError()
}
}
}
internal fun Scheme.mergeWith(schemes: List): Scheme {
if (schemes.isEmpty()) return this
val lazyScheme = LazyScheme(this)
val bindings = lazyScheme.bindings
fun unifySchemes(a: LazyScheme, b: LazyScheme) {
bindings.unify(a.target, b.target)
for ((ap, bp) in a.parameters.zip(b.parameters)) {
unifySchemes(ap, bp)
}
}
schemes.forEach {
val overrideScheme = LazyScheme(it, bindings = lazyScheme.bindings)
unifySchemes(lazyScheme, overrideScheme)
}
return lazyScheme.toScheme()
}
