Remove ExtensionMethodAccess and revert all dataflow changes

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -550,23 +550,12 @@ private module ControlFlowGraphImpl {
       or
       index = 0 and result = this.(RValue).getQualifier() and not result instanceof TypeAccess
       or
-      exists(Call e | e = this and not e instanceof ExtensionMethodAccess |
+      exists(Call e | e = this |
         index = -1 and result = e.getQualifier() and not result instanceof TypeAccess
         or
         result = e.getArgument(index)
       )
       or
-      exists(ExtensionMethodAccess e | e = this |
-        // the actual qualifier of the expression method access
-        index = -1 and result = e.getImplicitQualifier() and not result instanceof TypeAccess
-        or
-        // the extension receiver
-        index = 0 and result = e.getQualifier()
-        or
-        // the arguments
-        result = e.getArgument(index - 1)
-      )
-      or
       exists(StringTemplateExpr e | e = this | result = e.getComponent(index))
       or
       index = 0 and result = this.(ClassExpr).getExpr()

java/ql/lib/semmle/code/java/Expr.qll

@@ -1984,27 +1984,6 @@ class MethodAccess extends Expr, Call, @methodaccess {
   override string getAPrimaryQlClass() { result = "MethodAccess" }
 }
 
-/**
- * An invocation of a Kotlin `ExtensionMethod`.
- */
-class ExtensionMethodAccess extends MethodAccess {
-  ExtensionMethodAccess() { this.getMethod() instanceof ExtensionMethod }
-
-  /**
-   * Gets the implicit qualifier of this extension method access. This expression
-   * is the qualifier of this method access in bytecode.
-   */
-  Expr getImplicitQualifier() { result.isNthChildOf(this, -1) }
-
-  // The syntactic qualifier of an extension method is its receiver (arg 0),
-  // whereas the actual arguments begin at index 1.
-  override Expr getQualifier() { result.isNthChildOf(this, 0) }
-
-  override Expr getAnArgument() { result = this.getArgument(_) }
-
-  override Expr getArgument(int index) { result = super.getArgument(index + 1) and index >= 0 }
-}
-
 /** A type access is a (possibly qualified) reference to a type. */
 class TypeAccess extends Expr, Annotatable, @typeaccess {
   /** Gets the qualifier of this type access, if any. */
@@ -2246,11 +2225,8 @@ private module Qualifier {
 
     /** Gets the qualifier of this member access, if any. */
     Expr getQualifier() {
-      result = this.(FieldAccess).getQualifier()
-      or
-      result = this.(MethodAccess).getQualifier() and not this instanceof ExtensionMethodAccess
-      or
-      result = this.(ExtensionMethodAccess).getImplicitQualifier()
+      result = this.(FieldAccess).getQualifier() or
+      result = this.(MethodAccess).getQualifier()
     }
   }
 

java/ql/lib/semmle/code/java/Variable.qll

@@ -108,20 +108,7 @@ class Parameter extends Element, @param, LocalScopeVariable {
   pragma[noinline]
   private Expr getACallArgument(int i) {
     exists(Call call |
-      (
-        exists(int idx |
-          (
-            idx = i and not call instanceof ExtensionMethodAccess
-            or
-            idx = i - 1 and call instanceof ExtensionMethodAccess
-          ) and
-          result = call.getArgument(idx)
-        )
-        or
-        i = 0 and
-        call instanceof ExtensionMethodAccess and
-        result = call.getQualifier()
-      ) and
+      result = call.getArgument(i) and
       call.getCallee().getSourceDeclaration().getAParameter() = this
     )
   }

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowNodes.qll

@@ -49,16 +49,10 @@ newtype TNode =
 
 private predicate explicitInstanceArgument(Call call, Expr instarg) {
   call instanceof MethodAccess and
-  instarg = getQualifier(call) and
+  instarg = call.getQualifier() and
   not call.getCallee().isStatic()
 }
 
-private Expr getQualifier(MethodAccess ma) {
-  not ma instanceof ExtensionMethodAccess and result = ma.getQualifier()
-  or
-  result = ma.(ExtensionMethodAccess).getImplicitQualifier()
-}
-
 private predicate implicitInstanceArgument(Call call, InstanceAccessExt ia) {
   ia.isImplicitMethodQualifier(call) or
   ia.isImplicitThisConstructorArgument(call)
@@ -366,9 +360,6 @@ module Private {
     ArgumentNode() {
       exists(Argument arg | this.asExpr() = arg | not arg.isVararg())
       or
-      // In JVM bytecode the qualifier of an extension method call is the 0th argument
-      exists(ExtensionMethodAccess ema | this.asExpr() = ema.getQualifier())
-      or
       this instanceof ImplicitVarargsArray
       or
       this = getInstanceArgument(_)
@@ -382,20 +373,7 @@ module Private {
      */
     predicate argumentOf(DataFlowCall call, int pos) {
       exists(Argument arg | this.asExpr() = arg |
-        call.asCall() = arg.getCall() and
-        (
-          pos = arg.getPosition() and not call.asCall() instanceof ExtensionMethodAccess
-          or
-          // Shift the positions of an extension method call by 1 to make space for the qualifier at index 0.
-          pos = arg.getPosition() + 1 and call.asCall() instanceof ExtensionMethodAccess
-        )
-      )
-      or
-      // In JVM bytecode the qualifier of an extension method call is the 0th argument
-      exists(ExtensionMethodAccess ema |
-        call.asCall() = ema and
-        pos = 0 and
-        this.asExpr() = ema.getQualifier()
+        call.asCall() = arg.getCall() and pos = arg.getPosition()
       )
       or
       call.asCall() = this.(ImplicitVarargsArray).getCall() and

java/ql/lib/semmle/code/java/dispatch/VirtualDispatch.qll

@@ -273,14 +273,8 @@ private module Dispatch {
     not e instanceof FunctionalExpr and result = e.getType()
   }
 
-  private Expr getQualifier(MethodAccess ma) {
-    not ma instanceof ExtensionMethodAccess and result = ma.getQualifier()
-    or
-    result = ma.(ExtensionMethodAccess).getImplicitQualifier()
-  }
-
   private predicate hasQualifierType(VirtualMethodAccess ma, RefType t, boolean exact) {
-    exists(Expr src | src = variableTrack(getQualifier(ma)) |
+    exists(Expr src | src = variableTrack(ma.getQualifier()) |
       // If we have a qualifier, then we track it through variable assignments
       // and take the type of the assigned value.
       exists(RefType srctype | srctype = getPreciseType(src) |

java/ql/test/kotlin/library-tests/extensions/methodaccesses.expected

@@ -1,10 +1,18 @@
 | extensions.kt:21:17:21:38 | someClassMethod(...) | extensions.kt:21:5:21:15 | new SomeClass(...) | extensions.kt:21:34:21:36 | foo |
-| extensions.kt:22:17:22:30 | someFun(...) | extensions.kt:22:5:22:15 | new SomeClass(...) | extensions.kt:22:26:22:28 | foo |
-| extensions.kt:23:17:23:30 | bothFun(...) | extensions.kt:23:5:23:15 | new SomeClass(...) | extensions.kt:23:26:23:28 | foo |
-| extensions.kt:24:17:24:35 | bothFunDiffTypes(...) | extensions.kt:24:5:24:15 | new SomeClass(...) | extensions.kt:24:34:24:34 | 1 |
+| extensions.kt:22:17:22:30 | someFun(...) | extensions.kt:22:17:22:30 | ExtensionsKt | extensions.kt:22:5:22:15 | new SomeClass(...) |
+| extensions.kt:22:17:22:30 | someFun(...) | extensions.kt:22:17:22:30 | ExtensionsKt | extensions.kt:22:26:22:28 | foo |
+| extensions.kt:23:17:23:30 | bothFun(...) | extensions.kt:23:17:23:30 | ExtensionsKt | extensions.kt:23:5:23:15 | new SomeClass(...) |
+| extensions.kt:23:17:23:30 | bothFun(...) | extensions.kt:23:17:23:30 | ExtensionsKt | extensions.kt:23:26:23:28 | foo |
+| extensions.kt:24:17:24:35 | bothFunDiffTypes(...) | extensions.kt:24:17:24:35 | ExtensionsKt | extensions.kt:24:5:24:15 | new SomeClass(...) |
+| extensions.kt:24:17:24:35 | bothFunDiffTypes(...) | extensions.kt:24:17:24:35 | ExtensionsKt | extensions.kt:24:34:24:34 | 1 |
 | extensions.kt:25:20:25:44 | anotherClassMethod(...) | extensions.kt:25:5:25:18 | new AnotherClass(...) | extensions.kt:25:40:25:42 | foo |
-| extensions.kt:26:20:26:36 | anotherFun(...) | extensions.kt:26:5:26:18 | new AnotherClass(...) | extensions.kt:26:32:26:34 | foo |
-| extensions.kt:27:20:27:33 | bothFun(...) | extensions.kt:27:5:27:18 | new AnotherClass(...) | extensions.kt:27:29:27:31 | foo |
-| extensions.kt:28:20:28:42 | bothFunDiffTypes(...) | extensions.kt:28:5:28:18 | new AnotherClass(...) | extensions.kt:28:38:28:40 | foo |
-| extensions.kt:29:18:29:27 | bar(...) | extensions.kt:29:6:29:15 | someString | extensions.kt:29:23:29:25 | foo |
-| extensions.kt:31:18:31:32 | baz(...) | extensions.kt:31:6:31:15 | someString | extensions.kt:31:23:31:30 | bazParam |
+| extensions.kt:26:20:26:36 | anotherFun(...) | extensions.kt:26:20:26:36 | ExtensionsKt | extensions.kt:26:5:26:18 | new AnotherClass(...) |
+| extensions.kt:26:20:26:36 | anotherFun(...) | extensions.kt:26:20:26:36 | ExtensionsKt | extensions.kt:26:32:26:34 | foo |
+| extensions.kt:27:20:27:33 | bothFun(...) | extensions.kt:27:20:27:33 | ExtensionsKt | extensions.kt:27:5:27:18 | new AnotherClass(...) |
+| extensions.kt:27:20:27:33 | bothFun(...) | extensions.kt:27:20:27:33 | ExtensionsKt | extensions.kt:27:29:27:31 | foo |
+| extensions.kt:28:20:28:42 | bothFunDiffTypes(...) | extensions.kt:28:20:28:42 | ExtensionsKt | extensions.kt:28:5:28:18 | new AnotherClass(...) |
+| extensions.kt:28:20:28:42 | bothFunDiffTypes(...) | extensions.kt:28:20:28:42 | ExtensionsKt | extensions.kt:28:38:28:40 | foo |
+| extensions.kt:29:18:29:27 | bar(...) | extensions.kt:29:18:29:27 | ExtensionsKt | extensions.kt:29:6:29:15 | someString |
+| extensions.kt:29:18:29:27 | bar(...) | extensions.kt:29:18:29:27 | ExtensionsKt | extensions.kt:29:23:29:25 | foo |
+| extensions.kt:31:18:31:32 | baz(...) | extensions.kt:31:18:31:32 | new (...) | extensions.kt:31:6:31:15 | someString |
+| extensions.kt:31:18:31:32 | baz(...) | extensions.kt:31:18:31:32 | new (...) | extensions.kt:31:23:31:30 | bazParam |

java/ql/test/kotlin/library-tests/extensions/methodaccesses.ql

@@ -1,7 +1,7 @@
 import java
 
-// For ExtensionMethodAccess:
-// * qualifier is the child with index 0 instead of -1
-// * arguments are children starting from index 1 instead of 0
+// For extension methods we use JVM bytecode representation:
+// * the qualifier is the dispatch receiver expression, and
+// * the extension receiver expression is the 0th argument.
 from MethodAccess ma
 select ma, ma.getQualifier(), ma.getAnArgument()