fix: correctly sniper-print type member comments after removal of all modifiers

src/main/java/spoon/support/sniper/internal/AbstractSourceFragmentPrinter.java

@@ -58,7 +58,7 @@ public void print(PrinterEvent event) {
 		if (index != -1) { // means we have found a source code fragment corresponding to this event
 
 			// we print all spaces and comments before this fragment
-			printSpaces(getLastNonSpaceNonCommentBefore(index), index);
+			printSpaces(getLastNonSpaceNonCommentBefore(index, prevIndex), index);
 
 			SourceFragment fragment = childFragments.get(index);
 			event.printSourceFragment(fragment, isFragmentModified(fragment));
@@ -306,17 +306,39 @@ protected void printStandardSpaces() {
 		separatorActions.clear();
 	}
 
-	private int getLastNonSpaceNonCommentBefore(int index) {
+	private int getLastNonSpaceNonCommentBefore(int index, int prevIndex) {
 		for (int i = index - 1; i >= 0; i--) {
 			SourceFragment fragment = childFragments.get(i);
-			if (isSpaceFragment(fragment) || isCommentFragment(fragment)) {
+			if (isSpaceFragment(fragment)
+					|| isCommentFragment(fragment)
+					|| isRecentlySkippedModifierCollectionFragment(i, prevIndex)) {
 				continue;
 			}
 			return i + 1;
 		}
 		return 0;
 	}
 
+	/**
+	 * Determines if the fragment at index is a "recently skipped" collection fragment
+	 * containing modifiers. "Recently skipped" entails that the modifier fragment has not been
+	 * printed, and that the last printed fragment occurs before the modifier fragment.
+	 *
+	 * It is necessary to detect such fragments as whitespace and comments may otherwise be lost
+	 * when completely removing modifier lists. See issue #3732 for details.
+	 *
+	 * @param index Index of the fragment.
+	 * @param prevIndex Index of the last printed fragment.
+	 * @return true if the fragment is a recently skipped collection fragment with modifiers.
+	 */
+	private boolean isRecentlySkippedModifierCollectionFragment(int index, int prevIndex) {
+		SourceFragment fragment = childFragments.get(index);
+		return prevIndex < index
+				&& fragment instanceof CollectionSourceFragment
+				&& ((CollectionSourceFragment) fragment).getItems().stream()
+						.anyMatch(ElementSourceFragment::isModifierFragment);
+	}
+
 	@Override
 	public void onPush() {
 	}

src/main/java/spoon/support/sniper/internal/ElementSourceFragment.java

@@ -898,4 +898,11 @@ static boolean isCommentFragment(SourceFragment fragment) {
 		return fragment instanceof ElementSourceFragment && ((ElementSourceFragment) fragment).getElement() instanceof CtComment;
 	}
 
+	/**
+	 * @return true if {@link SourceFragment} represents a modifier
+	 */
+	static boolean isModifierFragment(SourceFragment fragment) {
+		return fragment instanceof ElementSourceFragment
+				&& ((ElementSourceFragment) fragment).getRoleInParent() == CtRole.MODIFIER;
+	}
 }

src/test/java/spoon/test/prettyprinter/TestSniperPrinter.java

@@ -60,6 +60,7 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import static org.hamcrest.CoreMatchers.allOf;
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.anyOf;
 import static org.hamcrest.MatcherAssert.assertThat;
@@ -435,6 +436,27 @@ public void testNewlineInsertedBetweenModifiedCommentAndTypeMemberWithAddedModif
 		testSniper("TypeMemberComments", enactModifications, assertCommentCorrectlyPrinted);
 	}
 
+	@Test
+	public void testTypeMemberCommentDoesNotDisappearWhenAllModifiersAreRemoved() {
+		// contract: A comment on a field should not disappear when all of its modifiers are removed.
+
+		Consumer<CtType<?>> removeTypeMemberModifiers = type -> {
+			type.getField("NON_FINAL_FIELD").setModifiers(Collections.emptySet());
+			type.getMethodsByName("nonStaticMethod").get(0).setModifiers(Collections.emptySet());
+			type.getNestedType("NonStaticInnerClass").setModifiers(Collections.emptySet());
+		};
+
+		BiConsumer<CtType<?>, String> assertFieldCommentPrinted = (type, result) ->
+			assertThat(result, allOf(
+						containsString("// field comment\n    int NON_FINAL_FIELD"),
+						containsString("// method comment\n    void nonStaticMethod"),
+						containsString("// nested type comment\n    class NonStaticInnerClass")
+					)
+			);
+
+		testSniper("TypeMemberComments", removeTypeMemberModifiers, assertFieldCommentPrinted);
+	}
+
 	@Test
 	public void testAddedImportStatementPlacedOnSeparateLineInFileWithoutPackageStatement() {
 		// contract: newline must be inserted between import statements when a new one is added