fix: use strict patterns for synthetic methods inline (#1829)

jadx-core/src/main/java/jadx/core/dex/instructions/args/InsnArg.java

@@ -264,6 +264,13 @@ public abstract class InsnArg extends Typed {
 		return false;
 	}
 
+	public boolean isSameVar(RegisterArg arg) {
+		if (isRegister()) {
+			return ((RegisterArg) this).sameRegAndSVar(arg);
+		}
+		return false;
+	}
+
 	protected final <T extends InsnArg> T copyCommonParams(T copy) {
 		copy.copyAttributesFrom(this);
 		copy.setParentInsn(parentInsn);

jadx-core/src/main/java/jadx/core/dex/visitors/MarkMethodsForInline.java

@@ -80,13 +80,47 @@ public class MarkMethodsForInline extends AbstractVisitor {
 			return addInlineAttr(mth, insn);
 		}
 		if (insnsCount == 2 && insns.get(1).getType() == InsnType.RETURN) {
-			// synthetic field setter
-			return addInlineAttr(mth, insns.get(0));
+			InsnNode firstInsn = insns.get(0);
+			InsnNode retInsn = insns.get(1);
+			if (retInsn.getArgsCount() == 0
+					|| isSyntheticAccessPattern(mth, firstInsn, retInsn)) {
+				return addInlineAttr(mth, firstInsn);
+			}
 		}
 		// TODO: inline field arithmetics. Disabled tests: TestAnonymousClass3a and TestAnonymousClass5
 		return null;
 	}
 
+	private static boolean isSyntheticAccessPattern(MethodNode mth, InsnNode firstInsn, InsnNode retInsn) {
+		List<RegisterArg> mthRegs = mth.getArgRegs();
+		switch (firstInsn.getType()) {
+			case IGET:
+				return mthRegs.size() == 1
+						&& retInsn.getArg(0).isSameVar(firstInsn.getResult())
+						&& firstInsn.getArg(0).isSameVar(mthRegs.get(0));
+			case SGET:
+				return mthRegs.size() == 0
+						&& retInsn.getArg(0).isSameVar(firstInsn.getResult());
+
+			case IPUT:
+				return mthRegs.size() == 2
+						&& retInsn.getArg(0).isSameVar(mthRegs.get(1))
+						&& firstInsn.getArg(0).isSameVar(mthRegs.get(1))
+						&& firstInsn.getArg(1).isSameVar(mthRegs.get(0));
+			case SPUT:
+				return mthRegs.size() == 1
+						&& retInsn.getArg(0).isSameVar(mthRegs.get(0))
+						&& firstInsn.getArg(0).isSameVar(mthRegs.get(0));
+
+			case INVOKE:
+				return mthRegs.size() >= 1
+						&& firstInsn.getArg(0).isSameVar(mthRegs.get(0))
+						&& retInsn.getArg(0).isSameVar(firstInsn.getResult());
+			default:
+				return false;
+		}
+	}
+
 	private static MethodInlineAttr addInlineAttr(MethodNode mth, InsnNode insn) {
 		if (!fixVisibilityOfInlineCode(mth, insn)) {
 			return null;

jadx-core/src/main/java/jadx/core/dex/visitors/shrink/CodeShrinkVisitor.java

@@ -9,6 +9,8 @@ import java.util.Set;
 
 import jadx.core.dex.attributes.AFlag;
 import jadx.core.dex.instructions.InsnType;
+import jadx.core.dex.instructions.InvokeCustomNode;
+import jadx.core.dex.instructions.InvokeNode;
 import jadx.core.dex.instructions.args.InsnArg;
 import jadx.core.dex.instructions.args.InsnWrapArg;
 import jadx.core.dex.instructions.args.Named;
@@ -123,6 +125,9 @@ public class CodeShrinkVisitor extends AbstractVisitor {
 				return;
 			}
 		}
+		if (!checkLambdaInline(arg, assignInsn)) {
+			return;
+		}
 
 		int assignPos = insnList.getIndex(assignInsn);
 		if (assignPos != -1) {
@@ -145,6 +150,26 @@ public class CodeShrinkVisitor extends AbstractVisitor {
 		}
 	}
 
+	/**
+	 * Forbid inline lambda into invoke as an instance arg, i.e. this will not compile:
+	 * {@code () -> { ... }.apply(); }
+	 */
+	private static boolean checkLambdaInline(RegisterArg arg, InsnNode assignInsn) {
+		if (assignInsn.getType() == InsnType.INVOKE && assignInsn instanceof InvokeCustomNode) {
+			for (RegisterArg useArg : arg.getSVar().getUseList()) {
+				InsnNode parentInsn = useArg.getParentInsn();
+				if (parentInsn != null && parentInsn.getType() == InsnType.INVOKE) {
+					InvokeNode invokeNode = (InvokeNode) parentInsn;
+					InsnArg instArg = invokeNode.getInstanceArg();
+					if (instArg != null && instArg == useArg) {
+						return false;
+					}
+				}
+			}
+		}
+		return true;
+	}
+
 	private static boolean varWithSameNameExists(MethodNode mth, SSAVar inlineVar) {
 		for (SSAVar ssaVar : mth.getSVars()) {
 			if (ssaVar == inlineVar || ssaVar.getCodeVar() == inlineVar.getCodeVar()) {

jadx-core/src/test/java/jadx/tests/integration/java8/TestLambdaReturn.java

@@ -0,0 +1,61 @@
+package jadx.tests.integration.java8;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.tests.api.IntegrationTest;
+import jadx.tests.api.extensions.profiles.TestProfile;
+import jadx.tests.api.extensions.profiles.TestWithProfiles;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestLambdaReturn extends IntegrationTest {
+
+	@SuppressWarnings("unused")
+	public static class TestCls {
+		interface Function0<R> {
+			R apply();
+		}
+
+		public static class T2 {
+			public long l;
+
+			public T2(long l) {
+				this.l = l;
+			}
+
+			public void w() {
+			}
+		}
+
+		public Byte test(Byte b1) {
+			Function0<Void> f1 = () -> {
+				new T2(94L).w();
+				return null;
+			};
+			f1.apply();
+			return null;
+		}
+	}
+
+	@TestWithProfiles(TestProfile.DX_J8)
+	public void test() {
+		assertThat(getClassNode(TestCls.class))
+				.code()
+				.containsLines(2,
+						"Function0<Void> f1 = () -> {",
+						indent() + "new T2(94L).w();",
+						indent() + "return null;",
+						"};");
+	}
+
+	@TestWithProfiles(TestProfile.D8_J11_DESUGAR)
+	public void testLambda() {
+		getClassNode(TestCls.class);
+	}
+
+	@Test
+	public void testNoDebug() {
+		noDebugInfo();
+		getClassNode(TestCls.class);
+	}
+}