[Analysis API] introduce substitutor builder

analysis/analysis-api/src/org/jetbrains/kotlin/analysis/api/KtAnalysisSession.kt

@@ -151,6 +151,11 @@ public abstract class KtAnalysisSession(final override val token: KtLifetimeToke
     internal val scopeSubstitution: KtScopeSubstitution get() = scopeSubstitutionImpl
     protected abstract val scopeSubstitutionImpl: KtScopeSubstitution
 
+    @KtAnalysisApiInternals
+    public val substitutorFactory: KtSubstitutorFactory get() = substitutorFactoryImpl
+    protected abstract val substitutorFactoryImpl: KtSubstitutorFactory
+
+
     @PublishedApi
     internal val typesCreator: KtTypeCreator
         get() = typesCreatorImpl

analysis/analysis-api/src/org/jetbrains/kotlin/analysis/api/components/KtSubstitutorFactory.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.analysis.api.components
+
+import org.jetbrains.kotlin.analysis.api.KtAnalysisApiInternals
+import org.jetbrains.kotlin.analysis.api.KtAnalysisSession
+import org.jetbrains.kotlin.analysis.api.lifetime.KtLifetimeOwner
+import org.jetbrains.kotlin.analysis.api.lifetime.KtLifetimeToken
+import org.jetbrains.kotlin.analysis.api.lifetime.assertIsValidAndAccessible
+import org.jetbrains.kotlin.analysis.api.lifetime.withValidityAssertion
+import org.jetbrains.kotlin.analysis.api.symbols.KtTypeParameterSymbol
+import org.jetbrains.kotlin.analysis.api.types.KtSubstitutor
+import org.jetbrains.kotlin.analysis.api.types.KtType
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
+
+public abstract class KtSubstitutorFactory : KtAnalysisSessionComponent() {
+    public abstract fun buildSubstitutor(builder: KtSubstitutorBuilder): KtSubstitutor
+}
+
+@OptIn(ExperimentalContracts::class, KtAnalysisApiInternals::class)
+public inline fun KtAnalysisSession.buildSubstitutor(
+    build: KtSubstitutorBuilder.() -> Unit
+): KtSubstitutor {
+    contract {
+        callsInPlace(build, InvocationKind.EXACTLY_ONCE)
+    }
+    return analysisSession.substitutorFactory.buildSubstitutor(KtSubstitutorBuilder(token).apply(build))
+}
+
+
+public class KtSubstitutorBuilder
+@KtAnalysisApiInternals constructor(override val token: KtLifetimeToken) : KtLifetimeOwner {
+    private val _mapping = mutableMapOf<KtTypeParameterSymbol, KtType>()
+
+    public val mappings: Map<KtTypeParameterSymbol, KtType> get() = withValidityAssertion { _mapping }
+
+    public fun substitution(typeParameter: KtTypeParameterSymbol, type: KtType) {
+        assertIsValidAndAccessible()
+        _mapping[typeParameter] = type
+    }
+
+    public fun substitutions(substitutions: Map<KtTypeParameterSymbol, KtType>) {
+        assertIsValidAndAccessible()
+        _mapping += substitutions
+    }
+}
+
+

analysis/analysis-api/testData/components/substitutorFactory/substitutorBuilder/function.kt

@@ -0,0 +1 @@
+fun <A, B, C> A.fo<caret>oo(x: List<B>): C

analysis/analysis-api/testData/components/substitutorFactory/substitutorBuilder/function.txt

@@ -0,0 +1,9 @@
+KtDeclaration: KtNamedFunction
+Symbol:
+fun <A, B, C> A.fooo(x: kotlin.collections.List<B>): C
+
+Substitutor:
+A -> kotlin.Int, B -> kotlin.Long, C -> kotlin.collections.List<kotlin.String>
+
+Signature after substitution:
+kotlin.Int.fooo(x: kotlin.collections.List<kotlin.Long>): kotlin.collections.List<kotlin.String>