optimized alternative collapsing

only collapse alternative if the result is smaller than the uncollapsed
version

org.eclipse.xtext.tests/src/org/eclipse/xtext/xtext/generator/hoisting/HoistingProcessorTest.java

@@ -802,7 +802,25 @@ public class HoistingProcessorTest extends AbstractXtextTests {
 		assertFalse(guard.isTrivial());
 		assertTrue(guard.hasTerminal());
 		
-		assertEquals("(" + keyword("a", 2) + " || " + keyword("b", 1) + " || ((p0) && (p2))) && (" + keyword("b", 2) + " || " + keyword("b", 1) + " || ((p0) && (p3))) && (" + keyword("a", 1) + " || (p1))", guard.render());
+		// collapsed version is actually not optimal
+		//assertEquals("(" + keyword("a", 2) + " || " + keyword("b", 1) + " || ((p0) && (p2))) && (" + keyword("b", 2) + " || " + keyword("b", 1) + " || ((p0) && (p3))) && (" + keyword("a", 1) + " || (p1))", guard.render());
+		assertEquals(
+				"(" + 
+					keyword("b", 1) + " || " +
+					"(" +
+						"(p0) && (" +
+							keyword("a", 2) + " || " +
+							"(p2)" + 
+						") && (" + 
+							keyword("b", 2) + " || " +
+							"(p3)" + 
+						")" +
+					")" +
+				") && (" + 
+					keyword("a", 1) + " || " + 
+					"(p1)" + 
+				")",
+			guard.render());
 	}
 	
 	// currently not able to find optimal solution
@@ -833,7 +851,27 @@ public class HoistingProcessorTest extends AbstractXtextTests {
 		//assertEquals("(" + keyword("a", 1) + " || (" + keyword("c", 3) + " && " + eof(3) + ") || ((p0) && (p2))) && (" + keyword("c", 1) + " || ((p0) && (p3))) && (" + keyword("d", 3) + " || (p1))", guard.render());
 		
 		// still valid but non-optimal
-		assertEquals("(" + keyword("a", 1) + " || (" + keyword("a", 3)+ " && " + keyword("b", 3) + " && " + keyword("c", 3) + " && " + eof(3) + ") || ((p0) && (p2))) && (" + keyword("b", 1) + " || (" + keyword("a", 3)+ " && " + keyword("b", 3) + " && " + keyword("c", 3) + " && " + eof(3) + ") || ((p0) && (p3))) && (" + keyword("d", 3) + " || (p1))", guard.render());
+		assertEquals(
+				"(" + 
+					"(" +
+						keyword("a", 3) + " && " +
+						keyword("b", 3) + " && " +
+						keyword("c", 3) + " && " +
+						eof(3) + 
+					") || (" +
+						"(p0) && (" +
+							keyword("a", 1) + " || " +
+							"(p2)" +
+						") && (" +
+							keyword("b", 1) + " || " +
+							"(p3)" +
+						")" +
+					")" + 
+				") && (" +
+					keyword("d", 3) + " || " +
+					"(p1)" +
+				")",
+			guard.render());
 	}
 	
 	@Test

org.eclipse.xtext.xtext.generator/src/org/eclipse/xtext/xtext/generator/parser/antlr/hoisting/guards/hoistingGuards/AlternativesGuard.java

@@ -31,9 +31,19 @@ public class AlternativesGuard implements HoistingGuard {
 	}
 	
 	public AlternativesGuard(List<PathGuard> paths) {
+		// collapsing nested alternatives might reduce output size
+		// -> try both and use smaller one
+		
+		this.paths = paths;
+		int lengthWithoutCollapse = render().length();
 		this.paths = PathGuard.collapse(paths);
+		int lengthWithCollapse = render().length();
+		
+		if (lengthWithoutCollapse < lengthWithCollapse)
+			this.paths = paths;
 	}
 	
+	
 	// package private so PathGuard can access this method
 	List<PathGuard> getPaths() {
 		return paths;

org.eclipse.xtext.xtext.generator/src/org/eclipse/xtext/xtext/generator/parser/antlr/hoisting/guards/tokenGuards/TokenSequenceGuard.java

@@ -28,8 +28,10 @@ public class TokenSequenceGuard implements TokenGuard {
 	
 	public TokenSequenceGuard(Collection<? extends TokenGuard> sequence) {
 		Set<Integer> checkedPositions = new HashSet<>();
+		// remove all guards from sequences who's positions are already in the sequence
 		this.sequence = sequence.stream()
 				.flatMap(g -> {
+					// special case: reduce TokenSequenceGuards
 					if (g instanceof TokenSequenceGuard) {
 						return ((TokenSequenceGuard) g).sequence.stream()
 								.filter(s -> !s.getPositions().stream()
@@ -65,7 +67,7 @@ public class TokenSequenceGuard implements TokenGuard {
 	@Override
 	public String render() {
 		if (sequence.size() == 1) {
-		return sequence.stream().findAny().get().render();
+			return sequence.stream().findAny().get().render();
 		} else {
 			return render(ContextConnective.DISJUNCTION);
 		}