Fix lambda statement recovery in AST generated by ASTParser

Also, recover expressions as an expression statement.

i.e. when there is this source in a method:

```java
{
    ...
    "String".var
    ...
...
}
```

jdt.ui expects it to be recovered like this:

```java
{
    ...
    "String".var = $missing$;
    ...
```

Where `$missing$` is a fake, empty identifier.

Currently, in some cases, the `"String".var` is being completely
discarded, and this should improve that.

Related to #4530

Signed-off-by: David Thompson <[email protected]>

Author: datho7561

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/parser/Parser.java

@@ -1138,6 +1138,13 @@ public RecoveredElement buildInitialRecoveryState(){
 	}
 
 	if (this.statementRecoveryActivated) {
+		if (this.expressionPtr >= 0 && this.expressionStack[0] instanceof FieldReference fr) {
+			var snr = new SingleNameReference(new char[0], fr.sourceEnd);
+			snr.sourceStart = fr.sourceEnd;
+			var assignment = new Assignment(fr, snr, fr.sourceEnd);
+			assignment.statementEnd = assignment.sourceEnd;
+			element = element.add(assignment, 0);
+		}
 		if (this.pendingRecoveredType != null &&
 				this.scanner.startPosition - 1 <= this.pendingRecoveredType.declarationSourceEnd) {
 			// Add the pending type to the AST if this type isn't already added in the AST.
@@ -12086,12 +12093,18 @@ public void parse(MethodDeclaration md, CompilationUnitDeclaration unit) {
 		return;
 
 	boolean oldMethodRecoveryActivated = this.methodRecoveryActivated;
+
 	if(this.options.performMethodsFullRecovery) {
 		// we should not relocate bodyStart if there is a block within the statements
 		this.ignoreNextOpeningBrace = true;
 		this.methodRecoveryActivated = true;
 		this.rParenPos = md.sourceEnd;
 	}
+	boolean oldStatementRecoveryActivated = this.statementRecoveryActivated;
+	if (this.options.performStatementsRecovery) {
+		this.statementRecoveryActivated = true;
+	}
+
 	initialize();
 	goForBlockStatementsopt();
 	this.nestedMethod[this.nestedType]++;
@@ -12108,9 +12121,12 @@ public void parse(MethodDeclaration md, CompilationUnitDeclaration unit) {
 		this.lastAct = ERROR_ACTION;
 	} finally {
 		this.nestedMethod[this.nestedType]--;
-		if(this.options.performStatementsRecovery) {
+		if (this.options.performStatementsRecovery) {
 			this.methodRecoveryActivated = oldMethodRecoveryActivated;
 		}
+		if (this.options.performStatementsRecovery) {
+			this.statementRecoveryActivated = oldStatementRecoveryActivated;
+		}
 	}
 
 	checkNonNLSAfterBodyEnd(md.declarationSourceEnd);

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/dom/StandAloneASTParserTest.java

@@ -92,6 +92,7 @@ public void testBug529654_001() {
 		ModuleDeclaration module = unit.getModule();
 		assertTrue("Incorrect Module Name", module.getName().getFullyQualifiedName().equals("m"));
 	}
+
 	public void test1() {
 		String contents =
 				"package p;\n" +
@@ -2026,4 +2027,49 @@ public static void main(String[] args) {
             }
         }
 	}
+
+	public void testGH4530_001() {
+		String contents =
+				"""
+				package p;
+				import java.util.function.Function;
+				public class X {
+					public static void main(String[] args) {
+						Function<Integer, Integer> myFunc = a -> a;
+						System.out.println("yippeeee!");
+						word
+					}
+				}
+				""";
+		ASTNode node = runConversion(AST_JLS_LATEST, contents, true, true, true, "p/X.java");
+		assertTrue("should be compilation unit", node instanceof CompilationUnit);
+		CompilationUnit unit = (CompilationUnit)node;
+		TypeDeclaration typeDecl = (TypeDeclaration)unit.types().get(0);
+		MethodDeclaration methodDecl = (MethodDeclaration)typeDecl.getMethods()[0];
+		Block block = methodDecl.getBody();
+		assertEquals(block.statements().size(), 2);
+	}
+
+	public void testGH4530_002() {
+		String contents =
+				"""
+				package p;
+				import java.util.stream.Stream;
+				public class X {
+					public static void main(String[] args) {
+						int a = 4;
+						Stream.iterate(0,i -> ++i).limit(10);
+						"String".var
+					}
+				}
+				""";
+		ASTNode node = runConversion(AST_JLS_LATEST, contents, true, true, true, "p/X.java");
+		assertTrue("should be compilation unit", node instanceof CompilationUnit);
+		CompilationUnit unit = (CompilationUnit)node;
+		TypeDeclaration typeDecl = (TypeDeclaration)unit.types().get(0);
+		MethodDeclaration methodDecl = (MethodDeclaration)typeDecl.getMethods()[0];
+		Block block = methodDecl.getBody();
+		assertEquals(block.statements().size(), 3);
+		assertTrue(block.statements().get(2) instanceof ExpressionStatement);
+	}
 }

org.eclipse.jdt.core/codeassist/org/eclipse/jdt/internal/codeassist/complete/CompletionParser.java

@@ -6326,6 +6326,12 @@ protected CompilationUnitDeclaration endParse(int act) {
 						}
 						element = element.parent;
 					}
+				} else if (method.statements != null) {
+					// "double" recovery; base parser recovered statements and assist parser recovered the assist node
+					Statement[] newStatements = new Statement[method.statements.length + 1];
+					System.arraycopy(method.statements, 0, newStatements, 0, method.statements.length);
+					newStatements[method.statements.length] = statement;
+					method.statements = newStatements;
 				}
 			}
 		}

org.eclipse.jdt.core/codeassist/org/eclipse/jdt/internal/codeassist/impl/AssistParser.java

@@ -2070,6 +2070,8 @@ public void parseBlockStatements(MethodDeclaration md, CompilationUnitDeclaratio
 	if ((md.modifiers & ExtraCompilerModifiers.AccSemicolonBody) != 0)
 		return;
 
+	boolean oldStateRecoveryActivated = this.statementRecoveryActivated;
+	this.statementRecoveryActivated = true;
 	initialize();
 	// set the lastModifiers to reflect the modifiers of the method whose
 	// block statements are being parsed
@@ -2090,6 +2092,7 @@ public void parseBlockStatements(MethodDeclaration md, CompilationUnitDeclaratio
 		this.lastAct = ERROR_ACTION;
 	} finally {
 		this.nestedMethod[this.nestedType]--;
+		this.statementRecoveryActivated = oldStateRecoveryActivated;
 	}
 
 	if (this.lastAct == ERROR_ACTION) {