core[patch]: Account for escaped variables in mustache templates (langchain-ai#5775)

Author: bracesproul

langchain-core/src/prompts/template.ts

@@ -85,7 +85,9 @@ const mustacheTemplateToNodes = (
     if (temp[0] === "name") {
       const name = temp[1].includes(".") ? temp[1].split(".")[0] : temp[1];
       return { type: "variable", name };
-    } else if (temp[0] === "#") {
+    } else if (["#", "&"].includes(temp[0])) {
+      // # represents a section, "&" represents an unescaped variable.
+      // These should both be considered variables.
       return { type: "variable", name: temp[1] };
     } else {
       return { type: "literal", text: temp[1] };

langchain-core/src/prompts/tests/prompt.mustache.test.ts

@@ -1,5 +1,6 @@
 import { test, expect } from "@jest/globals";
 import { PromptTemplate } from "../prompt.js";
+import { parseTemplate } from "../template.js";
 
 test("Single input variable.", async () => {
   const template = "This is a {{foo}} test.";
@@ -91,3 +92,24 @@ hello
 is a test.`);
   expect(promptWithRepeats.inputVariables).toEqual(["foo"]);
 });
+
+test("Escaped variables", async () => {
+  const template = `test: {{{text}}}`;
+  const parsed = parseTemplate(template, "mustache");
+  expect(parsed[0]).toStrictEqual({
+    type: "literal",
+    text: "test: ",
+  });
+  expect(parsed[1]).toStrictEqual({
+    type: "variable",
+    name: "text",
+  });
+
+  const promptTemplate = PromptTemplate.fromTemplate(template, {
+    templateFormat: "mustache",
+  });
+  const result = await promptTemplate.invoke({
+    text: `hello i have a "quote`,
+  });
+  expect(result.value).toBe(`test: hello i have a "quote`);
+});