Kotlin: specialise extension receivers the same as other function parameters

This arises when a generic class extends one of its parameters; for example, `class G<T> { val T.v; get() = 1 }`, where specialisation `G<List>` should generate a method specialisation `getV(List)`.

Author: smowton

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -1188,22 +1188,16 @@ open class KotlinFileExtractor(
                             id
 
                 val extReceiver = f.extensionReceiverParameter
-                val idxOffset = if (extReceiver != null) 1 else 0
-                val fParameters = overriddenAttributes?.valueParameters ?: f.valueParameters
+                val fParameters = (overriddenAttributes?.valueParameters ?: f.valueParameters) + listOfNotNull(extReceiver)
                 val paramTypes = fParameters.mapIndexed { i, vp ->
-                    extractValueParameter(vp, id, i + idxOffset, typeSubstitution, sourceDeclaration, classTypeArgsIncludingOuterClasses, extractTypeAccess = extractMethodAndParameterTypeAccesses, overriddenAttributes?.sourceLoc)
+                    extractValueParameter(vp, id, i, typeSubstitution, sourceDeclaration, classTypeArgsIncludingOuterClasses, extractTypeAccess = extractMethodAndParameterTypeAccesses, overriddenAttributes?.sourceLoc)
                 }
-                val allParamTypes = if (extReceiver != null) {
-                    val extendedType = useType(extReceiver.type)
+                if (extReceiver != null) {
+                    val extendedType = paramTypes[0]
                     tw.writeKtExtensionFunctions(id.cast<DbMethod>(), extendedType.javaResult.id, extendedType.kotlinResult.id)
-
-                    val t = extractValueParameter(extReceiver, id, 0, null, sourceDeclaration, classTypeArgsIncludingOuterClasses, extractTypeAccess = extractMethodAndParameterTypeAccesses, overriddenAttributes?.sourceLoc)
-                    listOf(t) + paramTypes
-                } else {
-                    paramTypes
                 }
 
-                val paramsSignature = allParamTypes.joinToString(separator = ",", prefix = "(", postfix = ")") { signatureOrWarn(it.javaResult, f) }
+                val paramsSignature = paramTypes.joinToString(separator = ",", prefix = "(", postfix = ")") { signatureOrWarn(it.javaResult, f) }
 
                 val adjustedReturnType = addJavaLoweringWildcards(getAdjustedReturnType(f), false, (javaCallable as? JavaMethod)?.returnType)
                 val substReturnType = typeSubstitution?.let { it(adjustedReturnType, TypeContext.RETURN, pluginContext) } ?: adjustedReturnType

java/ql/integration-tests/posix-only/kotlin/generic-extension-property/User.java

@@ -0,0 +1,9 @@
+public class User {
+
+  public static void test(KotlinClass<String> kc) {
+
+    kc.getKotlinVal("Hello world");
+
+  }
+
+}

java/ql/integration-tests/posix-only/kotlin/generic-extension-property/test.expected

@@ -0,0 +1,4 @@
+| User.java:5:5:5:34 | getKotlinVal(...) | getKotlinVal | String |
+| test.kt:8:43:8:78 | with(...) | with | Function1<? super T,? extends R> |
+| test.kt:8:43:8:78 | with(...) | with | T |
+| test.kt:8:68:8:76 | getKotlinVal(...) | getKotlinVal | String |

java/ql/integration-tests/posix-only/kotlin/generic-extension-property/test.kt

@@ -0,0 +1,8 @@
+class KotlinClass<T> {
+
+  val T.kotlinVal: Int
+    get() = 1
+
+}
+
+fun kotlinUser(kc: KotlinClass<String>) = with(kc) { "hello world".kotlinVal }

java/ql/integration-tests/posix-only/kotlin/generic-extension-property/test.py

@@ -0,0 +1,4 @@
+from create_database_utils import *
+
+os.mkdir('build')
+run_codeql_database_create(["kotlinc test.kt -d build", "javac User.java -cp build"], lang="java")

java/ql/integration-tests/posix-only/kotlin/generic-extension-property/test.ql

@@ -0,0 +1,4 @@
+import java
+
+from MethodAccess ma
+select ma, ma.getCallee().toString(), ma.getCallee().getAParamType().toString()