Added automatic discovery mechanism for partials

hbs.js

@@ -2,23 +2,84 @@
 
 import Handlebars from 'handlebars';
 
+/**
+ * Attaches the precompiled Handlebars template in a CommonJs module,
+ * and attaches any depended partials on `load` for system.js to
+ * fetch. Also registers the partials as such on the Handlebars
+ * runtime.
+ */
 export function translate(load) {
-  let precompiled = Handlebars.precompile(load.source);
-  let handlebarsRuntimePath = System.normalizeSync('handlebars/handlebars.runtime.js', __moduleName);
 
-  // in builds we want to embed the canonical name for the handlebars runtime
-  if (System.getCanonicalName) {
-    handlebarsRuntimePath = System.getCanonicalName(handlebarsRuntimePath);
-  }
+  let ast = Handlebars.parse(load.source);
+  let partials = findPartials(ast);
+  load.metadata.deps = partials;
+
+  let precompiled = Handlebars.precompile(load.source);
+  let handlebarsRuntimePath = System.normalizeSync('handlebars/handlebars.runtime', __moduleName);
 
   let output;
   if (load.metadata.format === 'esm') {
-    output = `import {Handlebars} from '${handlebarsRuntimePath}'; \n export default Handlebars.template(${precompiled});`;
+    let partialReqs = partials.map((dep, i) => {
+      return `import tmpl$i from '${dep}';`;
+    }).join('\n');
+    let registry = partials.map((dep, i) => {
+      return `Handlebars.registerPartial('${dep}', tmpl${i});`;
+    }).join('\n');
+
+    output = `
+import {Handlebars} from '${handlebarsRuntimePath}';
+${partialReqs}
+${registry}
+export default Handlebars.template(${precompiled});
+`;
   } else if (load.metadata.format === 'amd') {
-    output = `define(['${handlebarsRuntimePath}'], function (Handlebars) { return Handlebars.template(${precompiled}); });`;
+    let partialReqs = partials.map(dep => `'${dep}'`).join(', ');
+    let args = partials.map((dep, i) => `tmpl${i}`).join(', ');
+    let registry = partials.map((dep, i) => {
+      return `Handlebars.registerPartial('${dep}', tmpl${i});`;
+    }).join('\n  ');
+
+    output = `
+define(['${handlebarsRuntimePath}', ${partialReqs}],
+       function(Handlebars, ${args}) {
+  ${registry};
+  return Handlebars.template(${precompiled});
+});
+`;
   } else {
-    output = `var Handlebars = require('${handlebarsRuntimePath}'); \n module.exports = Handlebars.template(${precompiled});`;
+    let partialReqs = partials.map(dep => {
+      return `Handlebars.registerPartial('${dep}', require('${dep}'));`;
+    }).join('\n');
+    output = `
+var Handlebars = require('${handlebarsRuntimePath}');
+${partialReqs};
+module.exports = Handlebars.template(${precompiled});
+`;
   }
   load.source = output;
   return output;
 }
+
+/**
+ * Recursively trawls a Handlebars AST, providing the string names of
+ * all invoked partials.
+ */
+function findPartials(astRoot) {
+  let partials = [];
+
+  let recurse = function(ast) {
+    if (!ast) {
+      return;
+    } else if (Array.isArray(ast)) {
+      ast.forEach(n => recurse(n));
+    } else if (ast.type === 'PartialStatement') {
+      partials.push(ast.name.original);
+    } else if (typeof ast === 'object') {
+      let subnodes = Object.keys(ast).map(k => ast[k]);
+      subnodes.forEach(n => recurse(n));
+    }
+  };
+  recurse(astRoot);
+
+  return partials;
+}