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fix(core): Filter empty content blocks from formatted prompts #8688

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Merged
merged 1 commit into from
Aug 12, 2025
Merged

fix(core): Filter empty content blocks from formatted prompts #8688

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12 changes: 7 additions & 5 deletions langchain-core/src/prompts/chat.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -642,11 +642,13 @@ class _StringImageMessagePromptTemplate<
// eslint-disable-next-line @typescript-eslint/no-explicit-any
additionalContentFields = prompt.additionalContentFields as any;
}
content.push({
...additionalContentFields,
type: "text",
text: formatted,
});
if (formatted !== "") {
content.push({
...additionalContentFields,
type: "text",
text: formatted,
});
}
/** @TODO replace this */
// eslint-disable-next-line no-instanceof/no-instanceof
} else if (prompt instanceof ImagePromptTemplate) {
Expand Down
281 changes: 281 additions & 0 deletions langchain-core/src/prompts/tests/chat.mustache.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ import { AIMessage } from "../../messages/ai.js";
import { HumanMessage } from "../../messages/human.js";
import { SystemMessage } from "../../messages/system.js";
import { ChatPromptTemplate, HumanMessagePromptTemplate } from "../chat.js";
import { load } from "../../load/index.js";

test("Test creating a chat prompt template from role string messages", async () => {
const template = ChatPromptTemplate.fromMessages(
Expand Down Expand Up @@ -199,3 +200,283 @@ test("with ChatPromptTemplate", async () => {
`System: ${expectedResult}`
);
});

test("Rendering a prompt with conditionals doesn't result in empty text blocks", async () => {
const manifest = {
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "chat", "ChatPromptTemplate"],
kwargs: {
messages: [
{
lc: 1,
type: "constructor",
id: [
"langchain_core",
"prompts",
"chat",
"SystemMessagePromptTemplate",
],
kwargs: {
prompt: {
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template: "Always echo back whatever I send you.",
},
},
},
},
{
lc: 1,
type: "constructor",
id: [
"langchain_core",
"prompts",
"chat",
"HumanMessagePromptTemplate",
],
kwargs: {
prompt: [
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template: "Here is the teacher's prompt:",
additional_content_fields: {
text: "Here is the teacher's prompt:",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["promptDescription"],
template_format: "mustache",
template: '"{{promptDescription}}"\n',
additional_content_fields: {
text: '"{{promptDescription}}"\n',
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template:
"Here is the expected answer or success criteria given by the teacher:",
additional_content_fields: {
text: "Here is the expected answer or success criteria given by the teacher:",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["expectedResponse"],
template_format: "mustache",
template: '"{{expectedResponse}}"\n',
additional_content_fields: {
text: '"{{expectedResponse}}"\n',
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template:
"Note: This may be just one example many possible correct ways for the student to respond.\n",
additional_content_fields: {
text: "Note: This may be just one example many possible correct ways for the student to respond.\n",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template: "For your evaluation of the student's response:\n",
additional_content_fields: {
text: "For your evaluation of the student's response:\n",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template:
"Here is a transcript of the student's explanation:",
additional_content_fields: {
text: "Here is a transcript of the student's explanation:",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["responseTranscript"],
template_format: "mustache",
template: '"{{responseTranscript}}"\n',
additional_content_fields: {
text: '"{{responseTranscript}}"\n',
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["readingFluencyAnalysis"],
template_format: "mustache",
template:
"{{#readingFluencyAnalysis}} For this task, the student's reading pronunciation and fluency were important. Here is analysis of the student's oral response: \"{{readingFluencyAnalysis}}\" {{/readingFluencyAnalysis}}",
additional_content_fields: {
text: "{{#readingFluencyAnalysis}} For this task, the student's reading pronunciation and fluency were important. Here is analysis of the student's oral response: \"{{readingFluencyAnalysis}}\" {{/readingFluencyAnalysis}}",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["readingFluencyAnalysis"],
template_format: "mustache",
template:
"{{#readingFluencyAnalysis}}Root analysis of the student's response (step 3) in this oral analysis rather than inconsistencies in the transcript.{{/readingFluencyAnalysis}}",
additional_content_fields: {
text: "{{#readingFluencyAnalysis}}Root analysis of the student's response (step 3) in this oral analysis rather than inconsistencies in the transcript.{{/readingFluencyAnalysis}}",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["readingFluencyAnalysis"],
template_format: "mustache",
template:
"{{#readingFluencyAnalysis}}Remember this is a student, so we care about general fluency - not voice acting. {{/readingFluencyAnalysis}}\n",
additional_content_fields: {
text: "{{#readingFluencyAnalysis}}Remember this is a student, so we care about general fluency - not voice acting. {{/readingFluencyAnalysis}}\n",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: ["multipleChoiceAnalysis"],
template_format: "mustache",
template:
"{{#multipleChoiceAnalysis}}Here is an analysis of the student's multiple choice response: {{multipleChoiceAnalysis}}{{/multipleChoiceAnalysis}}\n",
additional_content_fields: {
text: "{{#multipleChoiceAnalysis}}Here is an analysis of the student's multiple choice response: {{multipleChoiceAnalysis}}{{/multipleChoiceAnalysis}}\n",
},
},
},
{
lc: 1,
type: "constructor",
id: ["langchain_core", "prompts", "prompt", "PromptTemplate"],
kwargs: {
input_variables: [],
template_format: "mustache",
template: "Here is the student's whiteboard:\n",
additional_content_fields: {
text: "Here is the student's whiteboard:\n",
},
},
},
{
lc: 1,
type: "constructor",
id: [
"langchain_core",
"prompts",
"image",
"ImagePromptTemplate",
],
kwargs: {
template: {
url: "{{whiteboard}}",
},
input_variables: ["whiteboard"],
template_format: "mustache",
additional_content_fields: {
image_url: {
url: "{{whiteboard}}",
},
},
},
},
],
additional_options: {},
},
},
],
input_variables: [
"promptDescription",
"expectedResponse",
"responseTranscript",
"readingFluencyAnalysis",
"readingFluencyAnalysis",
"readingFluencyAnalysis",
"multipleChoiceAnalysis",
"whiteboard",
],
template_format: "mustache",
metadata: {
lc_hub_owner: "jacob",
lc_hub_repo: "mustache-conditionals",
lc_hub_commit_hash:
"836ad82d512409ea6024fb760b76a27ba58fc68b1179656c0ba2789778686d46",
},
},
};
const prompt = await load<ChatPromptTemplate>(JSON.stringify(manifest));
const res = await prompt.invoke({
promptDescription: "What is the capital of the USA?",
expectedResponse: "Washington, D.C.",
responseTranscript: "Washington, D.C.",
readingFluencyAnalysis: undefined,
multipleChoiceAnalysis: "testing2",
whiteboard: "https://foo.com/bar.png",
});
const content = res.messages[1].content;
expect(Array.isArray(content)).toBe(true);
const emptyTextBlocks = (content as Record<string, unknown>[]).filter(
(block: Record<string, unknown>) =>
block.type === "text" && block.text === ""
);
expect(emptyTextBlocks.length).toBe(0);
});
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