searchbar: adds searcher supports(string) function

Author: frauzufall

src/main/java/org/scijava/search/DefaultSearchOperation.java

@@ -130,10 +130,11 @@ public void invalidate() {
 		@Override
 		public void run() {
 			final boolean exclusive = searcher.exclusive(query);
+			final boolean supported = searcher.supports(query);
 			final boolean enabled = searchService.enabled(searcher);
 			if (!valid) return;
-			final List<SearchResult> results = enabled ? //
-				searcher.search(query, fuzzy) : Collections.emptyList();
+			final List<SearchResult> results = supported ? (enabled ? //
+				searcher.search(query, fuzzy) : Collections.emptyList()) : null;
 			if (!valid) return;
 			for (final SearchListener l : listeners) {
 				l.searchCompleted(new SearchEvent(searcher, results, exclusive));

src/main/java/org/scijava/search/Searcher.java

@@ -26,6 +26,11 @@ public interface Searcher extends SciJavaPlugin {
 	default boolean enabled() {
 		return true;
 	}
+	
+	/** Whether this plugin supports a search of this term. */
+	default boolean supports(String term) {
+		return true;
+	}
 
 	/** Gets whether this plugin wants exclusive rights to the given text. */
 	default boolean exclusive(@SuppressWarnings("unused") final String text) {

src/main/java/org/scijava/search/snippet/SnippetSearcher.java

@@ -64,6 +64,11 @@ public String title() {
 		// NB: A misnomer, but it's the term users are familiar with.
 		return "Code snippets";
 	}
+	
+	@Override
+	public boolean supports(final String text) {
+		return text.startsWith("#!") || text.startsWith("!");
+	}
 
 	@Override
 	public boolean exclusive(final String text) {

src/main/java/org/scijava/ui/swing/search/SwingSearchBar.java

@@ -463,6 +463,8 @@ private void rebuild() {
 				final List<SearchResult> completeResults = //
 					allResults.get(searcher.getClass()).results();
 
+				if (completeResults == null) continue;
+				
 				// Add section header.
 				listModel.addElement(new SearchResultHeader(searcher));