Allow Removing Standard GFM Alert Types

Author: rdestefa

CHANGELOG.md

@@ -20,6 +20,11 @@ with the exception that 0.x versions can break between minor versions.
     other blocks (including other alerts). See
     [this section of the alerts README](./commonmark-ext-gfm-alerts/README.md#nesting-alerts)
     for more information.
+  - New configuration for `AlertsExtension` to allow alert types (including standard
+    GFM types) to be removed (disallowed).
+    ```java
+    var extension = AlertsExtension.builder().removeTypes("NOTE", "TIP").build();
+    ```
 
 ## [0.28.0] - 2026-03-31
 ### Added

commonmark-ext-gfm-alerts/README.md

@@ -36,6 +36,13 @@ var extension = AlertsExtension.builder()
 
 Custom types must be UPPERCASE. Standard type titles can also be overridden for localization.
 
+If any types (including the five standard GFM types) aren't desired, they can be
+removed (disallowed):
+
+```java
+var extension = AlertsExtension.builder().removeTypes("NOTE", "TIP").build();
+```
+
 ### Custom Alert Titles
 
 Allow authors to provide custom titles per alert by adding text after the alert

commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/AlertsExtension.java

@@ -49,14 +49,28 @@
 public class AlertsExtension implements Parser.ParserExtension, HtmlRenderer.HtmlRendererExtension,
         MarkdownRenderer.MarkdownRendererExtension {
 
-    static final Set<String> STANDARD_TYPES = Set.of("NOTE", "TIP", "IMPORTANT", "WARNING", "CAUTION");
+    /**
+     * The standard GitHub Flavored Markdown (GFM) types that the extension
+     * enables by default. They can be removed individually with
+     * {@link Builder#removeTypes(String...)}.
+     */
+    public static final Map<String, String> STANDARD_TYPES = Map.ofEntries(
+        Map.entry("NOTE", "Note"),
+        Map.entry("TIP", "Tip"),
+        Map.entry("IMPORTANT", "Important"),
+        Map.entry("WARNING", "Warning"),
+        Map.entry("CAUTION", "Caution")
+    );
 
-    private final Map<String, String> customTypes;
+    /**
+     * A map of alert marker ({@code [!TYPE]}) to the default title for that marker.
+     */
+    private final Map<String, String> allowedTypes;
     private final boolean customTitlesAllowed;
     private final boolean nestedAlertsAllowed;
 
     private AlertsExtension(Builder builder) {
-        this.customTypes = new HashMap<>(builder.customTypes);
+        this.allowedTypes = new HashMap<>(builder.allowedTypes);
         this.customTitlesAllowed = builder.customTitlesAllowed;
         this.nestedAlertsAllowed = builder.nestedAlertsAllowed;
     }
@@ -71,15 +85,14 @@ public static Builder builder() {
 
     @Override
     public void extend(Parser.Builder parserBuilder) {
-        var allowedTypes = new HashSet<>(STANDARD_TYPES);
-        allowedTypes.addAll(customTypes.keySet());
+        var allowedTypesSet = new HashSet<>(allowedTypes.keySet());
         parserBuilder.customBlockParserFactory(
-            new AlertBlockParser.Factory(allowedTypes, customTitlesAllowed, nestedAlertsAllowed));
+            new AlertBlockParser.Factory(allowedTypesSet, customTitlesAllowed, nestedAlertsAllowed));
     }
 
     @Override
     public void extend(HtmlRenderer.Builder rendererBuilder) {
-        rendererBuilder.nodeRendererFactory(context -> new AlertHtmlNodeRenderer(context, customTypes));
+        rendererBuilder.nodeRendererFactory(context -> new AlertHtmlNodeRenderer(context, allowedTypes));
     }
 
     @Override
@@ -101,18 +114,18 @@ public Set<Character> getSpecialCharacters() {
      * Builder for configuring the alerts extension.
      */
     public static class Builder {
-        private final Map<String, String> customTypes = new HashMap<>();
+        private final Map<String, String> allowedTypes = new HashMap<>(STANDARD_TYPES);
         private boolean customTitlesAllowed = false;
         private boolean nestedAlertsAllowed = false;
 
         /**
-         * Adds a custom alert type with a display title.
+         * Adds a custom alert type with a default title.
          * <p>
-         * This can also be used to override the display title of standard GFM types
+         * This can also be used to override the default title of standard GFM types
          * (e.g., for localization).
          *
          * @param type the alert type (must be uppercase)
-         * @param title the display title for this alert type
+         * @param title the default title for this alert type
          * @return {@code this}
          */
         public Builder addCustomType(String type, String title) {
@@ -125,7 +138,34 @@ public Builder addCustomType(String type, String title) {
             if (!type.equals(type.toUpperCase(Locale.ROOT))) {
                 throw new IllegalArgumentException("Type must be uppercase: " + type);
             }
-            customTypes.put(type, title);
+            allowedTypes.put(type, title);
+            return this;
+        }
+
+        /**
+         * Removes alert types from the allowed list.
+         *
+         * @param types the alert types to remove (must be uppercase)
+         * @return {@code this}
+         * @see AlertsExtension#STANDARD_TYPES
+         */
+        public Builder removeTypes(String... types) {
+            if (types == null) {
+                throw new IllegalArgumentException("Types must not be null");
+            }
+
+            for (String type : types) {
+                if (type == null || type.isEmpty()) {
+                    throw new IllegalArgumentException("Each type must not be null or empty");
+                }
+
+                if (!type.equals(type.toUpperCase(Locale.ROOT))) {
+                    throw new IllegalArgumentException("Type must be uppercase: " + type);
+                }
+
+                allowedTypes.remove(type);
+            }
+
             return this;
         }
 

commonmark-ext-gfm-alerts/src/main/java/org/commonmark/ext/gfm/alerts/internal/AlertHtmlNodeRenderer.java

@@ -13,12 +13,12 @@ public class AlertHtmlNodeRenderer extends AlertNodeRenderer {
 
     private final HtmlWriter htmlWriter;
     private final HtmlNodeRendererContext context;
-    private final Map<String, String> customTypeTitles;
+    private final Map<String, String> allowedTypes;
 
-    public AlertHtmlNodeRenderer(HtmlNodeRendererContext context, Map<String, String> customTypeTitles) {
+    public AlertHtmlNodeRenderer(HtmlNodeRendererContext context, Map<String, String> allowedTypes) {
         this.htmlWriter = context.getWriter();
         this.context = context;
-        this.customTypeTitles = customTypeTitles;
+        this.allowedTypes = allowedTypes;
     }
 
     @Override
@@ -53,24 +53,11 @@ protected void renderAlert(Alert alert) {
     }
 
     private String getAlertTitle(String type) {
-        var customTypeTitle = customTypeTitles.get(type);
-        if (customTypeTitle != null) {
-            return customTypeTitle;
-        }
-        switch (type) {
-            case "NOTE":
-                return "Note";
-            case "TIP":
-                return "Tip";
-            case "IMPORTANT":
-                return "Important";
-            case "WARNING":
-                return "Warning";
-            case "CAUTION":
-                return "Caution";
-            default:
-                throw new IllegalStateException("Unknown alert type: " + type);
+        var typeTitle = allowedTypes.get(type);
+        if (typeTitle == null) {
+            throw new IllegalStateException("Unknown alert type: " + type);
         }
+        return typeTitle;
     }
 
     private void renderChildren(Node parent) {

commonmark-ext-gfm-alerts/src/test/java/org/commonmark/ext/gfm/alerts/AlertsTest.java

@@ -137,6 +137,31 @@ public void customTypeTitleMustNotBeEmpty() {
                 AlertsExtension.builder().addCustomType("INFO", "").build());
     }
 
+    @Test
+    public void removeStandardTypes() {
+        var extension = AlertsExtension.builder().removeTypes("NOTE", "TIP").build();
+        var parser = Parser.builder().extensions(Set.of(extension)).build();
+        var renderer = HtmlRenderer.builder().extensions(Set.of(extension)).build();
+
+        assertThat(renderer.render(parser.parse("> [!NOTE]\n> Regular block quote"))).isEqualTo(
+                "<blockquote>\n" +
+                "<p>[!NOTE]\n" +
+                "Regular block quote</p>\n" +
+                "</blockquote>\n");
+
+        assertThat(renderer.render(parser.parse("> [!TIP]\n> Regular block quote"))).isEqualTo(
+                "<blockquote>\n" +
+                "<p>[!TIP]\n" +
+                "Regular block quote</p>\n" +
+                "</blockquote>\n");
+
+        assertThat(renderer.render(parser.parse("> [!IMPORTANT]\n> Alert"))).isEqualTo(
+                "<div class=\"markdown-alert markdown-alert-important\" data-alert-type=\"important\">\n" +
+                "<p class=\"markdown-alert-title\">Important</p>\n" +
+                "<p>Alert</p>\n" +
+                "</div>\n");
+    }
+
     // Custom titles
 
     @Test