From 5147f38abb400d33a4aa49de5af5318835c60b88 Mon Sep 17 00:00:00 2001
From: Stephan Herrmann
Date: Sat, 18 May 2019 23:42:00 +0200
Subject: Bug 545420 - [1.8][inference] Receiving The target type of this
 expression must be a functional interface

Change-Id: Ia55c7f0399cdea0c4448a15bf835406ceb828977
---
 .../regression/GenericsRegressionTest_1_8.java     | 30 ++++++++++++++++++++++
 .../lookup/ConstraintExpressionFormula.java        |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/GenericsRegressionTest_1_8.java b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/GenericsRegressionTest_1_8.java
index 0b7af701e4..18ae2dd83b 100644
--- a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/GenericsRegressionTest_1_8.java
+++ b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/GenericsRegressionTest_1_8.java
@@ -9825,4 +9825,34 @@ public void testBug508834_comment0() {
 				"}\n"
 			});
 	}
+	public void testBug545420() {
+		runConformTest(
+			new String[] {
+				"Main.java",
+				"public class Main {\n" + 
+				"	public static void main(String[] args) {  \n" + 
+				"		System.out.println(new Main().getDetailCellCssFactory().getReturn());\n" + 
+				"	}\n" + 
+				"\n" + 
+				"	public FIReturnType getDetailCellCssFactory() {\n" + 
+				"		\n" + 
+				"		return 	method1(()-> {\n" + 
+				"					return  () ->{\n" + 
+				"							return \"something\";\n" + 
+				"					};\n" + 
+				"			});\n" + 
+				"	}\n" + 
+				"	\n" + 
+				"	public <X> X method1(FIWithGenerics<X> init) {\n" + 
+				"		return init.init();		\n" + 
+				"	}\n" + 
+				"}\n" + 
+				"interface FIReturnType {\n" + 
+				"	String getReturn();\n" + 
+				"}\n" + 
+				"interface FIWithGenerics<X> {\n" + 
+				"	 X init();\n" + 
+				"}\n"
+			});
+	}
 }
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ConstraintExpressionFormula.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ConstraintExpressionFormula.java
index 4e5e921e3d..c47c7249d8 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ConstraintExpressionFormula.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ConstraintExpressionFormula.java
@@ -157,6 +157,8 @@ class ConstraintExpressionFormula extends ConstraintFormula {
 			} else if (this.left instanceof LambdaExpression) {
 				LambdaExpression lambda = (LambdaExpression) this.left;
 				BlockScope scope = lambda.enclosingScope;
+				if (this.right instanceof InferenceVariable)
+					return TRUE; // assume inner inference will handle the fine print
 				if (!this.right.isFunctionalInterface(scope))
 					return FALSE;
 				
-- 
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