fix(console): add 'Assertion failed:' prefix to console.assert() with message

[murataslan1]

Summary

When console.assert(false, 'message') is called with arguments, it now correctly outputs Assertion failed: message instead of just message.

This matches the Node.js behavior per WHATWG Console specification.

What changed

Modified src/bun.js/ConsoleObject.zig to print the "Assertion failed: " prefix before the message arguments when message_type == .Assert.

Test

// Before: outputs 'message'
// After: outputs 'Assertion failed: message'
console.assert(false, 'message');

// Before: outputs 'value is 42'  
// After: outputs 'Assertion failed: value is 42'
console.assert(false, 'value is', 42);

References

• Fixes console.assert() with message should include "Assertion failed" alongside message #19953
• WHATWG Console Spec - Assert

[coderabbitai]

Walkthrough

Added a branch to ConsoleObject.messageWithTypeAndLevel that emits an "Assertion failed: " prefix (ANSI-colored when enabled) before console.assert messages with arguments; existing no-argument assertion behavior remains unchanged.

Changes

Cohort / File(s)	Change Summary
Console assertion output src/bun.js/ConsoleObject.zig	Added a branch in messageWithTypeAndLevel to write an "Assertion failed: " prefix when message_type == .Assert and arguments are present; prefix uses ANSI colors when enabled and is written via console.error_writer for Warning/Error levels or console.writer otherwise. Preserved early-return behavior for zero-argument asserts.

Pre-merge checks

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding 'Assertion failed:' prefix to console.assert() output with messages, which is the primary objective.
Description check	✅ Passed	The pull request description provides comprehensive information including summary, changes, test cases, and references, exceeding the minimal template requirements.
Linked Issues check	✅ Passed	The code changes directly address the objective from issue #19953 by adding the 'Assertion failed: ' prefix to console.assert() with message arguments, matching Node.js and WHATWG spec behavior.
Out of Scope Changes check	✅ Passed	All changes in ConsoleObject.zig are narrowly focused on the console.assert prefix feature described in the linked issue, with no extraneous modifications.

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• src/bun.js/ConsoleObject.zig (1 hunks)

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src/**/*.{cpp,zig}

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

src/**/*.{cpp,zig}: Use bun bd or bun run build:debug to build debug versions for C++ and Zig source files; creates debug build at ./build/debug/bun-debug
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Execute files using bun bd <file> <...args>; never use bun <file> directly as it will not include your changes
Enable debug logs for specific scopes using BUN_DEBUG_$(SCOPE)=1 environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required

Files:

• src/bun.js/ConsoleObject.zig

src/**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

Use bun.Output.scoped(.${SCOPE}, .hidden) for creating debug logs in Zig code

Implement core functionality in Zig, typically in its own directory in src/

src/**/*.zig: Private fields in Zig are fully supported using the # prefix: struct { #foo: u32 };
Use decl literals in Zig for declaration initialization: const decl: Decl = .{ .binding = 0, .value = 0 };
Prefer @import at the bottom of the file (auto formatter will move them automatically)

Be careful with memory management in Zig code - use defer for cleanup with allocators

Files:

• src/bun.js/ConsoleObject.zig

**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/zig-javascriptcore-classes.mdc)

**/*.zig: Expose generated bindings in Zig structs using pub const js = JSC.Codegen.JS<ClassName> with trait conversion methods: toJS, fromJS, and fromJSDirect
Use consistent parameter name globalObject instead of ctx in Zig constructor and method implementations
Use bun.JSError!JSValue return type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup using deinit() method that releases resources, followed by finalize() called by the GC that invokes deinit() and frees the pointer
Use JSC.markBinding(@src()) in finalize methods for debugging purposes before calling deinit()
For methods returning cached properties in Zig, declare external C++ functions using extern fn and callconv(JSC.conv) calling convention
Implement getter functions with naming pattern get<PropertyName> in Zig that accept this and globalObject parameters and return JSC.JSValue
Access JavaScript CallFrame arguments using callFrame.argument(i), check argument count with callFrame.argumentCount(), and get this with callFrame.thisValue()
For reference-counted objects, use .deref() in finalize instead of destroy() to release references to other JS objects

Files:

• src/bun.js/ConsoleObject.zig

🧠 Learnings (3)

📓 Common learnings

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/**/*.test.ts : Assert console messages using `c.expectMessage()` with single or multiple arguments; any unasserted logs fail the test to catch unexpected re-evaluations or reloads

📚 Learning: 2025-11-24T18:37:11.466Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Applies to src/js/{builtins,node,bun,thirdparty,internal}/**/*.{ts,js} : Use `$debug()` for debug logging and `$assert()` for assertions; both are stripped in release builds

Applied to files:

• src/bun.js/ConsoleObject.zig

📚 Learning: 2025-11-24T18:35:08.612Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/**/*.test.ts : Assert console messages using `c.expectMessage()` with single or multiple arguments; any unasserted logs fail the test to catch unexpected re-evaluations or reloads

Applied to files:

• src/bun.js/ConsoleObject.zig

🔇 Additional comments (1)

src/bun.js/ConsoleObject.zig (1)

159-170: Assert prefix logic and writer selection look correct

The new .Assert and len > 0 branch cleanly adds the "Assertion failed: " prefix only when there are message arguments, and uses the same writer selection as the main message so prefix and body go to the same stream. This aligns with the WHATWG/Node behavior without disturbing the existing no-arg assert path.

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Actionable comments posted: 1

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📒 Files selected for processing (1)

• src/bun.js/ConsoleObject.zig (1 hunks)

🧰 Additional context used

📓 Path-based instructions (3)

src/**/*.{cpp,zig}

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

src/**/*.{cpp,zig}: Use bun bd or bun run build:debug to build debug versions for C++ and Zig source files; creates debug build at ./build/debug/bun-debug
Run tests using bun bd test <test-file> with the debug build; never use bun test directly as it will not include your changes
Execute files using bun bd <file> <...args>; never use bun <file> directly as it will not include your changes
Enable debug logs for specific scopes using BUN_DEBUG_$(SCOPE)=1 environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required

Files:

• src/bun.js/ConsoleObject.zig

src/**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

Use bun.Output.scoped(.${SCOPE}, .hidden) for creating debug logs in Zig code

Implement core functionality in Zig, typically in its own directory in src/

src/**/*.zig: Private fields in Zig are fully supported using the # prefix: struct { #foo: u32 };
Use decl literals in Zig for declaration initialization: const decl: Decl = .{ .binding = 0, .value = 0 };
Prefer @import at the bottom of the file (auto formatter will move them automatically)

Be careful with memory management in Zig code - use defer for cleanup with allocators

Files:

• src/bun.js/ConsoleObject.zig

**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/zig-javascriptcore-classes.mdc)

**/*.zig: Expose generated bindings in Zig structs using pub const js = JSC.Codegen.JS<ClassName> with trait conversion methods: toJS, fromJS, and fromJSDirect
Use consistent parameter name globalObject instead of ctx in Zig constructor and method implementations
Use bun.JSError!JSValue return type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup using deinit() method that releases resources, followed by finalize() called by the GC that invokes deinit() and frees the pointer
Use JSC.markBinding(@src()) in finalize methods for debugging purposes before calling deinit()
For methods returning cached properties in Zig, declare external C++ functions using extern fn and callconv(JSC.conv) calling convention
Implement getter functions with naming pattern get<PropertyName> in Zig that accept this and globalObject parameters and return JSC.JSValue
Access JavaScript CallFrame arguments using callFrame.argument(i), check argument count with callFrame.argumentCount(), and get this with callFrame.thisValue()
For reference-counted objects, use .deref() in finalize instead of destroy() to release references to other JS objects

Files:

• src/bun.js/ConsoleObject.zig

🧠 Learnings (6)

📓 Common learnings

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/**/*.test.ts : Assert console messages using `c.expectMessage()` with single or multiple arguments; any unasserted logs fail the test to catch unexpected re-evaluations or reloads

📚 Learning: 2025-11-24T18:35:08.612Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/**/*.test.ts : Assert console messages using `c.expectMessage()` with single or multiple arguments; any unasserted logs fail the test to catch unexpected re-evaluations or reloads

Applied to files:

• src/bun.js/ConsoleObject.zig

📚 Learning: 2025-11-24T18:37:11.466Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Applies to src/js/{builtins,node,bun,thirdparty,internal}/**/*.{ts,js} : Use `$debug()` for debug logging and `$assert()` for assertions; both are stripped in release builds

Applied to files:

• src/bun.js/ConsoleObject.zig

📚 Learning: 2025-11-24T18:35:39.205Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Applies to src/bun.js/api/BunObject.zig : Implement getter functions in `src/bun.js/api/BunObject.zig` that return your feature, and export them in the `exportAll()` function

Applied to files:

• src/bun.js/ConsoleObject.zig

📚 Learning: 2025-11-24T18:36:59.706Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/V8*.cpp : Include ASSERT_V8_TYPE_LAYOUT_MATCHES(v8::ClassName) macro at the beginning of each V8 class implementation file to verify type layout compatibility with V8

Applied to files:

• src/bun.js/ConsoleObject.zig

📚 Learning: 2025-11-24T18:36:08.558Z

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/zig-javascriptcore-classes.mdc:0-0
Timestamp: 2025-11-24T18:36:08.558Z
Learning: Applies to **/*.zig : Use consistent parameter name `globalObject` instead of `ctx` in Zig constructor and method implementations

Applied to files:

• src/bun.js/ConsoleObject.zig