How to get diff colors in custom tool output

[dwood023]

Question

Using the custom tool helper, you can only return text (not other metadata I see related to the output of built-in tools like edit and write).

If this text contains markdown, it seems to get rendered successfully by opencode, allowing features such as bold or italic text to be outputted by custom tools. 😄

However, I have been trying to render output with colors, such as an embedded "diff":

import { tool } from "@opencode-ai/plugin";

export default tool({
	description: "Test if colored output works in custom tools",
	args: {},
	async execute(args) {
		const diffMarkdown = `\`\`\`diff
- This is a removed line
+ This is a new line
\`\`\``;
		return `Does **this** render in bold?\n\n${diffMarkdown}`;
	},
});

In the output, while the bold text renders correctly, the diff section is coloured uniformly, suggesting syntax highlighting doesn't work.

However, it actually works when I output a snippet of typescript.

import { tool } from "@opencode-ai/plugin";

export default tool({
	description: "Test if colored output works in custom tools",
	args: {},
	async execute(args) {
		const tsCode = `\`\`\`ts
function hello() {
  console.log("Hello");
}
\`\`\``;
		return `Does **this** render in bold?\n\n${tsCode}`;
	},
});

I tried to figure out exactly how syntax highlighting works in opencode, and found some packages such as marked and shiki involved. Shiki seems to bundle support for the diff format, so I would expect it to work.

One complication I see is that diffs are rendered separately in many places using @pierre/diffs, such as for the edit and write scripts. I thought about trying to leverage a similar mechanism to color my outputs, but it's not entirely appropriate for my use case, as my diffs are not really between files.

My use case is basically to run some test-like scripts through an opencode tool and have them color their outputs in green and red for easy readability by a human.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Feature: Integrate Glamour for syntax-highlighted markdown rendering #5915: Feature: Integrate Glamour for syntax-highlighted markdown rendering

This is about syntax highlighting for markdown code blocks (including diffs) in the UI. Your use case of colored diff/test output would likely be resolved by implementing proper syntax highlighting as described in that issue.

Feel free to ignore if this doesn't address your specific case.

[dwood023]

Also, I see the bash tool's output is not colorised like the output would be in a regular terminal. Is there any way to render the colors in opencode?