use mergeAdditionalFormats to provide custom defaults for cell handlers. Closes #1485

Author: cscheid

src/command/render/render-contexts.ts

@@ -499,13 +499,20 @@ async function resolveFormats(
     );
 
     // do the merge of the writer format into this format
-    if (extensionMetadata) {
-      mergedFormats[format] = mergeFormatMetadata(
+    mergedFormats[format] = mergeFormatMetadata(
+      defaultWriterFormat(formatDesc.formatWithVariants),
+      extensionMetadata[formatDesc.baseFormat],
+      userFormat,
+    );
+    //deno-lint-ignore no-explicit-any
+    mergedFormats[format].mergeAdditionalFormats = (...configs: any[]) => {
+      return mergeFormatMetadata(
         defaultWriterFormat(formatDesc.formatWithVariants),
         extensionMetadata[formatDesc.baseFormat],
+        ...configs,
         userFormat,
       );
-    }
+    };
   }
 
   // filter on formats supported by this project

src/config/types.ts

@@ -291,6 +291,18 @@ export interface Format {
   pandoc: FormatPandoc;
   language: FormatLanguage;
   metadata: Metadata;
+
+  /**
+   * mergeAdditionalFormats is populated by render-contexts, and
+   * are used to create a Format object with additional formats that
+   * have "less priority" than format information from user YAML.
+   *
+   * Use mergeAdditionalFormats to, e.g., set up custom defaults
+   * that are not driven by the output format.
+   */
+  //deno-lint-ignore no-explicit-any
+  mergeAdditionalFormats?: (...configs: any[]) => Format;
+
   resolveFormat?: (format: Format) => void;
   formatExtras?: (
     input: string,

src/core/handlers/base.ts

@@ -461,12 +461,22 @@ export const baseHandler: LanguageHandler = {
     handlerContext: LanguageCellHandlerContext,
     cells: QuartoMdCell[],
   ): Promise<MappedString[]> {
+    console.log(handlerContext);
     this.documentStart(handlerContext);
+    const mermaidExecute =
+      handlerContext.options.format.mergeAdditionalFormats!(
+        {
+          execute: this.defaultOptions,
+        },
+      ).execute;
     const result = await Promise.all(cells.map((cell) => {
       return this.cell(
         handlerContext,
         cell,
-        mergeConfigs(this.defaultOptions ?? {}, cell.options ?? {}),
+        mergeConfigs(
+          mermaidExecute as Record<string, unknown>,
+          cell.options ?? {},
+        ),
       );
     }));
     this.documentEnd(handlerContext);

src/core/handlers/mermaid.ts

@@ -81,6 +81,7 @@ object:
     cell: QuartoMdCell,
     options: Record<string, unknown>,
   ) {
+    console.log(options);
     const cellContent = handlerContext.cellContent(cell);
     // TODO escaping removes MappedString information.
     // create puppeteer target page