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Merged
haydenbleasel merged 4 commits into from
Mar 3, 2026
Merged

fix(code-block): preserve empty lines in code blocks #420

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518428f
fix(code-block): preserve empty lines in code blocks
Jiasm Feb 25, 2026
2c9bfd4
Fix lint issues
haydenbleasel Mar 3, 2026
dacc990
Add tests
haydenbleasel Mar 3, 2026
662e98d
Create fix-empty-lines.md
haydenbleasel Mar 3, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-empty-lines.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"streamdown": patch
---

Fix empty lines collapsing in highlighted code blocks
39 changes: 39 additions & 0 deletions packages/streamdown/__tests__/code-block-body.test.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,45 @@ describe("CodeBlockBody", () => {
expect(lineSpans.length).toBe(3);
});

it("should render newline for empty row (single empty-content token)", () => {
const result = {
tokens: [
[{ content: "line 1" }],
[{ content: "" }],
[{ content: "line 3" }],
],
};

const { container } = render(
<CodeBlockBody language="text" result={result} />
);

const lineSpans = container.querySelectorAll("code > span");
expect(lineSpans.length).toBe(3);

// Empty row should contain a newline, not a token span
const emptyLine = lineSpans[1];
expect(emptyLine?.querySelector("span")).toBeNull();
expect(emptyLine?.textContent).toBe("\n");
});

it("should render newline for empty row (zero tokens)", () => {
const result = {
tokens: [[{ content: "line 1" }], [], [{ content: "line 3" }]],
};

const { container } = render(
<CodeBlockBody language="text" result={result} />
);

const lineSpans = container.querySelectorAll("code > span");
expect(lineSpans.length).toBe(3);

const emptyLine = lineSpans[1];
expect(emptyLine?.querySelector("span")).toBeNull();
expect(emptyLine?.textContent).toBe("\n");
});

it("should handle token with color property", () => {
const result = {
tokens: [[{ content: "colored", color: "#abc123" }]],
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94 changes: 49 additions & 45 deletions packages/streamdown/lib/code-block/body.tsx
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Expand Up @@ -89,55 +89,59 @@ export const CodeBlockBody = memo(
// biome-ignore lint/suspicious/noArrayIndexKey: "This is a stable key."
key={index}
>
{/* biome-ignore lint/complexity/noExcessiveCognitiveComplexity: dual-theme token style mapping */}
{row.map((token, tokenIndex) => {
// Shiki dual-theme tokens put direct CSS properties (color,
// background-color) into htmlStyle alongside CSS custom
// properties (--shiki-dark, etc). Direct properties as inline
// styles override the Tailwind class-based dark mode approach,
// so we redirect them to CSS custom properties instead.
const tokenStyle: Record<string, string> = {};
let hasBg = Boolean(token.bgColor);
{row.length === 0 || (row.length === 1 && row[0].content === "")
? // Empty line: insert newline to preserve copy behavior
"\n"
: // biome-ignore lint/complexity/noExcessiveCognitiveComplexity: dual-theme token style mapping
row.map((token, tokenIndex) => {
// Shiki dual-theme tokens put direct CSS properties (color,
// background-color) into htmlStyle alongside CSS custom
// properties (--shiki-dark, etc). Direct properties as inline
// styles override the Tailwind class-based dark mode approach,
// so we redirect them to CSS custom properties instead.
const tokenStyle: Record<string, string> = {};
let hasBg = Boolean(token.bgColor);

if (token.color) {
tokenStyle["--sdm-c"] = token.color;
}
if (token.bgColor) {
tokenStyle["--sdm-tbg"] = token.bgColor;
}
if (token.color) {
tokenStyle["--sdm-c"] = token.color;
}
if (token.bgColor) {
tokenStyle["--sdm-tbg"] = token.bgColor;
}

if (token.htmlStyle) {
for (const [key, value] of Object.entries(
token.htmlStyle
)) {
if (key === "color") {
tokenStyle["--sdm-c"] = value;
} else if (key === "background-color") {
tokenStyle["--sdm-tbg"] = value;
hasBg = true;
} else {
tokenStyle[key] = value;
if (token.htmlStyle) {
for (const [key, value] of Object.entries(
token.htmlStyle
)) {
if (key === "color") {
tokenStyle["--sdm-c"] = value;
} else if (key === "background-color") {
tokenStyle["--sdm-tbg"] = value;
hasBg = true;
} else {
tokenStyle[key] = value;
}
}
}
}
}

return (
<span
className={cn(
"text-[var(--sdm-c,inherit)]",
"dark:text-[var(--shiki-dark,var(--sdm-c,inherit))]",
hasBg && "bg-[var(--sdm-tbg)]",
hasBg && "dark:bg-[var(--shiki-dark-bg,var(--sdm-tbg))]"
)}
// biome-ignore lint/suspicious/noArrayIndexKey: "This is a stable key."
key={tokenIndex}
style={tokenStyle as CSSProperties}
{...token.htmlAttrs}
>
{token.content}
</span>
);
})}
return (
<span
className={cn(
"text-[var(--sdm-c,inherit)]",
"dark:text-[var(--shiki-dark,var(--sdm-c,inherit))]",
hasBg && "bg-[var(--sdm-tbg)]",
hasBg &&
"dark:bg-[var(--shiki-dark-bg,var(--sdm-tbg))]"
)}
// biome-ignore lint/suspicious/noArrayIndexKey: "This is a stable key."
key={tokenIndex}
style={tokenStyle as CSSProperties}
{...token.htmlAttrs}
>
{token.content}
</span>
);
})}
</span>
))}
</code>
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