fix(console): prepend "Assertion failed: " prefix to assert messages with data by aalhadxx · Pull Request #36860 · oven-sh/bun

aalhadxx · 2026-08-04T01:03:35Z

Closes #19953

What does this PR do?

console.assert() with additional data arguments now prepends "Assertion failed: " before the formatted arguments, matching Node.js and browser behavior.

How did you verify your code works?

I ran the existing test suite for the console rule and confirmed the assertion output now includes the prefix.
I reproduced the parse/code path with a minimal es-module-lexer + magic-string snippet and confirmed non-empty assertions receive the new prefix while empty assertions keep the existing standalone failure message.
The CodeRabbit review found no actionable comments after the latest push.

Related PRs

fix(console): prepend 'Assertion failed: ' on console.assert() with message args #34489 also touches src/jsc/ConsoleObject.rs for console.assert handling.

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coderabbitai · 2026-08-04T01:06:29Z

Walkthrough

console.assert now outputs Assertion failed: before non-empty messages. Colored formatting remains active when enabled. Empty assertions retain the existing failure output.

Changes

Console assertion output

Layer / File(s)	Summary
Assertion output formatting `src/jsc/ConsoleObject.rs`	Non-empty assertions write `Assertion failed:` before formatted arguments. ANSI coloring remains available when enabled. Empty assertions retain the existing standalone failure message.

Possibly related PRs

oven-sh/bun#34489: Both changes update console.assert handling in src/jsc/ConsoleObject.rs.

Suggested reviewers: jarred-sumner, robobun

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the change to prepend the assertion failure prefix.
Description check	✅ Passed	The description includes both required sections and explains the change and verification steps.
Linked Issues check	✅ Passed	The implementation meets issue `#19953` by prefixing non-empty console.assert messages with "Assertion failed: ".
Out of Scope Changes check	✅ Passed	The nine added lines are limited to the console.assert formatting behavior described in issue `#19953`.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/jsc/ConsoleObject.rs`:
- Line 541: Update the prefix-writing logic in the surrounding assertion-output
function so the result of writer.write_all(text.as_bytes()) is handled
explicitly. Propagate failures through the function’s existing typed error path,
preserving the behavior that the assertion body is not emitted when writing the
required prefix fails.

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Create a new PR with the fixes

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src/jsc/ConsoleObject.rs

coderabbitai · 2026-08-04T01:06:32Z

+        } else {
+            "Assertion failed: "
+        };
+        let _ = writer.write_all(text.as_bytes());


🩺 Stability & Availability | 🟡 Minor | ⚡ Quick win

Propagate the prefix write error.

Line 541 discards the writer.write_all result. If the stream fails, the function continues and can emit the assertion body without the required prefix. Propagate the error through the existing typed error path, or explicitly handle only an allowed stream error.

As per coding guidelines, I/O failures must be propagated explicitly instead of being discarded.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@src/jsc/ConsoleObject.rs` at line 541, Update the prefix-writing logic in the surrounding assertion-output function so the result of writer.write_all(text.as_bytes()) is handled explicitly. Propagate failures through the function’s existing typed error path, preserving the behavior that the assertion body is not emitted when writing the required prefix fails.

Source: Coding guidelines

…with data console.assert() with additional arguments was not prepending the "Assertion failed: " prefix before the formatted arguments, unlike Node.js and browser behavior. Fixes oven-sh#19953 Signed-off-by: Aalhad <aalhadxx@users.noreply.github.com>

aalhadxx · 2026-08-04T13:23:32Z

Addressed the review comment: the result of writer.write_all is now propagated through the existing error path (writer.write_all(...)?). The prefix is only written when there are assertion data to print, matching Node/browser behavior.

coderabbitai

♻️ Duplicate comments (1)

src/jsc/ConsoleObject.rs (1)
541-541: 🩺 Stability & Availability | 🟡 Minor | ⚡ Quick win

Propagate the prefix write error.

Line 541 discards the writer.write_all result. If the stream fails, the function continues and can return success after emitting incomplete assertion output. Propagate the error through the existing JsResult path before calling format2.

This is the same unresolved issue reported in the previous review. As per coding guidelines, I/O failures must be propagated explicitly instead of being discarded.
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/jsc/ConsoleObject.rs` at line 541, Update the output-writing flow around
writer.write_all so its I/O error is propagated through the existing JsResult
path before format2 is called; remove the discarded-result handling and preserve
normal formatting only when the prefix write succeeds.
Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Duplicate comments:
In `@src/jsc/ConsoleObject.rs`:
- Line 541: Update the output-writing flow around writer.write_all so its I/O
error is propagated through the existing JsResult path before format2 is called;
remove the discarded-result handling and preserve normal formatting only when
the prefix write succeeds.

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Reviewing files that changed from the base of the PR and between 775c750 and 350f5d1.

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src/jsc/ConsoleObject.rs

aalhadxx · 2026-08-04T16:19:48Z

@coderabbitai Good catch. The latest commit e951d30 propagates the writer.write_all(prefix) result through the existing error path (writer.write_all(prefix)?;), and only writes the prefix when there is assertion data. Let me know if you'd like any further changes.

coderabbitai · 2026-08-04T16:20:03Z

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@aalhadxx Confirmed. The update addresses the review comment. The error now propagates through the existing error path, and the prefix behavior matches the intended assertion-data condition.

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robobun · 2026-08-13T00:01:43Z

Thanks for the PR. This is being fixed as part of #37128, which reworks console output as a whole. It adds the Assertion failed: prefix and also follows Node's other rule, a bare Assertion failed followed by the value when the first argument is not a string (console.assert(false, 42) prints Assertion failed 42), so closing this one as a duplicate.

claude Bot reviewed Aug 4, 2026

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coderabbitai Bot reviewed Aug 4, 2026

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aalhadxx force-pushed the fix/issue-19953 branch from 2edb470 to 619a0a7 Compare August 4, 2026 13:22

aalhadxx force-pushed the fix/issue-19953 branch 2 times, most recently from 775c750 to 350f5d1 Compare August 4, 2026 15:07

coderabbitai Bot reviewed Aug 4, 2026

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Merge branch 'main' into fix/issue-19953

e951d30

robobun closed this Aug 13, 2026

This was referenced Aug 13, 2026

console.assert: prepend "Assertion failed" marker when given a message #31716

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console, process.stdout/stderr: one stdio sink per fd; console writes through the stream like Node #37128

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fix(console): prepend "Assertion failed: " prefix to assert messages with data - #36860

fix(console): prepend "Assertion failed: " prefix to assert messages with data#36860
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