Add omitSingleParagraphP option to HtmlRenderer.Builder

This is useful for rendering single lines where wrapping in a <p> might be undesirable.
Fixes #150.

commonmark/src/main/java/org/commonmark/renderer/html/CoreHtmlNodeRenderer.java

@@ -69,13 +69,15 @@ public void visit(Heading heading) {
 
     @Override
     public void visit(Paragraph paragraph) {
-        boolean inTightList = isInTightList(paragraph);
-        if (!inTightList) {
+        boolean omitP = isInTightList(paragraph) || //
+                (context.shouldOmitSingleParagraphP() && paragraph.getParent() instanceof Document && //
+                        paragraph.getPrevious() == null && paragraph.getNext() == null);
+        if (!omitP) {
             html.line();
             html.tag("p", getAttrs(paragraph, "p"));
         }
         visitChildren(paragraph);
-        if (!inTightList) {
+        if (!omitP) {
             html.tag("/p");
             html.line();
         }

commonmark/src/main/java/org/commonmark/renderer/html/HtmlNodeRendererContext.java

@@ -17,8 +17,8 @@ public interface HtmlNodeRendererContext {
     /**
      * Let extensions modify the HTML tag attributes.
      *
-     * @param node the node for which the attributes are applied
-     * @param tagName the HTML tag name that these attributes are for (e.g. {@code h1}, {@code pre}, {@code code}).
+     * @param node       the node for which the attributes are applied
+     * @param tagName    the HTML tag name that these attributes are for (e.g. {@code h1}, {@code pre}, {@code code}).
      * @param attributes the attributes that were calculated by the renderer
      * @return the extended attributes with added/updated/removed entries
      */
@@ -47,6 +47,11 @@ public interface HtmlNodeRendererContext {
      */
     boolean shouldEscapeHtml();
 
+    /**
+     * @return whether documents that only contain a single paragraph should be rendered without the {@code <p>} tag
+     */
+    boolean shouldOmitSingleParagraphP();
+
     /**
      * @return true if the {@link UrlSanitizer} should be used.
      * @since 0.14.0

commonmark/src/main/java/org/commonmark/renderer/html/HtmlRenderer.java

@@ -22,17 +22,19 @@ public class HtmlRenderer implements Renderer {
 
     private final String softbreak;
     private final boolean escapeHtml;
+    private final boolean percentEncodeUrls;
+    private final boolean omitSingleParagraphP;
     private final boolean sanitizeUrls;
     private final UrlSanitizer urlSanitizer;
-    private final boolean percentEncodeUrls;
     private final List<AttributeProviderFactory> attributeProviderFactories;
     private final List<HtmlNodeRendererFactory> nodeRendererFactories;
 
     private HtmlRenderer(Builder builder) {
         this.softbreak = builder.softbreak;
         this.escapeHtml = builder.escapeHtml;
-        this.sanitizeUrls = builder.sanitizeUrls;
         this.percentEncodeUrls = builder.percentEncodeUrls;
+        this.omitSingleParagraphP = builder.omitSingleParagraphP;
+        this.sanitizeUrls = builder.sanitizeUrls;
         this.urlSanitizer = builder.urlSanitizer;
         this.attributeProviderFactories = new ArrayList<>(builder.attributeProviderFactories);
 
@@ -83,6 +85,7 @@ public static class Builder {
         private boolean sanitizeUrls = false;
         private UrlSanitizer urlSanitizer = new DefaultUrlSanitizer();
         private boolean percentEncodeUrls = false;
+        private boolean omitSingleParagraphP = false;
         private List<AttributeProviderFactory> attributeProviderFactories = new ArrayList<>();
         private List<HtmlNodeRendererFactory> nodeRendererFactories = new ArrayList<>();
 
@@ -166,6 +169,17 @@ public Builder percentEncodeUrls(boolean percentEncodeUrls) {
             return this;
         }
 
+        /**
+         * Whether documents that only contain a single paragraph should be rendered without the {@code <p>} tag. Set to
+         * {@code true} to render without the tag; the default of {@code false} always renders the tag.
+         *
+         * @return {@code this}
+         */
+        public Builder omitSingleParagraphP(boolean omitSingleParagraphP) {
+            this.omitSingleParagraphP = omitSingleParagraphP;
+            return this;
+        }
+
         /**
          * Add a factory for an attribute provider for adding/changing HTML attributes to the rendered tags.
          *
@@ -242,6 +256,11 @@ public boolean shouldEscapeHtml() {
             return escapeHtml;
         }
 
+        @Override
+        public boolean shouldOmitSingleParagraphP() {
+            return omitSingleParagraphP;
+        }
+
         @Override
         public boolean shouldSanitizeUrls() {
             return sanitizeUrls;

commonmark/src/test/java/org/commonmark/test/HtmlRendererTest.java

@@ -4,6 +4,8 @@
 import org.commonmark.parser.Parser;
 import org.commonmark.renderer.NodeRenderer;
 import org.commonmark.renderer.html.*;
+import org.commonmark.testutil.Asserts;
+import org.commonmark.testutil.RenderingTestCase;
 import org.commonmark.testutil.TestResources;
 import org.junit.Test;
 
@@ -308,6 +310,12 @@ public void canRenderContentsOfSingleParagraph() {
                 defaultRenderer().render(document));
     }
 
+    @Test
+    public void omitSingleParagraphP() {
+        var renderer = HtmlRenderer.builder().omitSingleParagraphP(true).build();
+        assertEquals("hi <em>there</em>", renderer.render(parse("hi *there*")));
+    }
+
     @Test
     public void threading() throws Exception {
         Parser parser = Parser.builder().build();