musubi-rs 0.3.0

A beautiful diagnostics renderer for compiler errors and warnings

Key Features • Installation • Quick Start • API Reference • Testing

📦 For Rust Users: This README covers the complete Musubi project (Lua/C/Rust implementations).
Looking for Rust API documentation? → See the comprehensive Rust API docs with examples and usage guides.
Rust crate: musubi-rs

Overview

Musubi (結び, "connection" in Japanese) is a high-performance diagnostics renderer inspired by Rust's Ariadne library. It produces beautiful, color-coded diagnostic messages with precise source location highlighting, multi-line spans, and intelligent label clustering.

Originally ported from Rust's Ariadne library, Musubi has evolved into a production-ready multi-language implementation:

C Library: High-performance core with Lua bindings (musubi.h, musubi.c)
Rust Crate: Safe FFI wrapper with ergonomic builder API (musubi-rs)

Both implementations produce identical output and are thoroughly tested (26 Rust unit tests + 30 doc tests, 100 Lua tests).

Key Features

✨ Beautiful Output

Multi-line diagnostics with color-coded labels
Intelligent label clustering and virtual row rendering
Unicode and CJK character support
ASCII/Unicode glyph sets for terminal compatibility

🚀 Performance Optimized

O(n) rendering complexity (vs original O(n²))
Pre-computed width caching for UTF-8 strings
Binary search for line windowing calculations
Zero-copy source file handling with streaming support

🎯 Improved Implementation

Cleaner Implement with seprated small functions
Bugfixes towards original Ariadne implement
New feature: Line limited support
New feature: No message label rendered

🛡️ Production Ready

100% test coverage (all reachable code covered)
Memory-safe C implementation
Comprehensive error handling
Tested on Lua 5.1, 5.4, and LuaJIT

Example

local mu = require "musubi"
local cg = mu.colorgen()

print(
    mu.report(12)
    :code "3"
    :title("Error", "Incompatible types")
    :label(33, 33):message("This is of type Nat"):color(cg:next())
    :label(43, 45):message("This is of type Str"):color(cg:next())
    :label(12, 48):message("This values are outputs of this match expression"):color(cg:next())
    :label(1, 48):message("The definition has a problem"):color(cg:next())
    :label(51, 76):message("Usage of definition here"):color(cg:next())
    :note "Outputs of match expressions must coerce to the same type"
    :source([[
def five = match () in {
	() => 5,
	() => "5",
}

def six =
    five
    + 1
]], "sample.tao")
    :render())

Output:

demo

Installation

Requirements

Rust Crate:

Rust 1.56+ (edition 2024)
No external dependencies (self-contained C implementation)

C Library with Lua Bindings:

C89-compatible compiler (GCC, Clang, MSVC)
Lua 5.1+ headers for Lua bindings
Optional: lcov for coverage reports

Building

Rust:

cargo add musubi-rs

C Library with Lua Bindings:

# Compile shared library
gcc -O3 -Wall -shared -fPIC -o musubi.so musubi.c -llua

# Or with coverage instrumentation
gcc -shared -fPIC --coverage -o musubi.so musubi.c -llua

macOS:

gcc -O3 -Wall -shared -undefined dynamic_lookup -o musubi.so musubi.c

Quick Start

Basic Usage (C Bindings)

local mu = require "musubi"

-- Create a color generator for automatic color cycling
local cg = mu.colorgen()

-- Build a report
local report = mu.report(14)  -- Primary error position
    :title("Error", "Something went wrong")
    :code("E001")
    :label(14, 14):message("This is the problem"):color(cg:next())
    :note("Try fixing this by...")
    :source("local x = 10 + 'hello'", "example.js")
    :render()

print(report)

Configuration

local mu = require "musubi"
local cfg = mu.config()
    :compact(true)            -- Enable compact mode
    :cross_gap(true)          -- Draw arrows across line gaps
    :tab_width(4)             -- Tab expansion width
    :limit_width(80)          -- Truncate long lines to 80 columns
    :char_set "unicode"       -- Use Unicode box-drawing characters
    :index_type "char"        -- Use character offsets (vs "byte")
    :ambi_width(1)            -- Ambiguous character width (1 or 2)
    :column_order(false)      -- Use natural label ordering (default)
    :align_messages(true)     -- Align label messages (default)

mu.report(0)
    :config(cfg)
    -- ... rest of report

Multi-Source Files

local mu = require "musubi"

mu.report(0)
    :label(10, 20, 1):message("Defined here")  -- src_id=1, first source
    :label(50, 60, 2):message("Used here")     -- src_id=2, second source
    :source("fn foo() { ... }", "foo.rs")
    :source("fn bar() { foo(); }", "bar.rs")
    :render()

File Sources (C Bindings Only)

local mu = require "musubi"
local io = require "io"

local fp = io.open("large_file.txt", "r")
mu.report(0)
    :source(fp, "large_file.txt")  -- Streams file on-demand
    :label(100, 150):message("Error in large file")
    :render()

Notice that if you use file handle on Windows, the musubi.so must not be built as static linking (/MT).

API Reference

Report Builder

Method	Description
`mu.report(pos, src_id?)`	Create a new report at position `pos`
`:title(level, message)`	Set report level (`"Error"`, `"Warning"`) and title
`:code(code)`	Set optional error code (e.g., `"E0308"`)
`:label(start, end?, src_id?)`	Add a label span (half-open interval `[start, end)`)
`:message(text, width?)`	Attach message to the last added label
`:color(color)`	Set color for the last added label
`:order(n)`	Set display order for the last label
`:priority(n)`	Set priority for clustering
`:note(text)`	Add a note to the footer
`:help(text)`	Add a help message to the footer
`:source(content, name?, offset?)`	Register a source (string or FILE*) with line offset (`0` default)
`:render(writer?)`	Render the report (returns string or calls writer function)

Configuration

Option	Type	Default	Description
`compact`	boolean	`false`	Compact mode (works with underlines)
`cross_gap`	boolean	`true`	Draw arrows across skipped lines
`underlines`	boolean	`true`	Draw underlines for single-line labels
`column_order`	boolean	`false`	Simple column order (true) vs natural ordering (false)
`align_messages`	boolean	`true`	Align label messages to same column
`multiline_arrows`	boolean	`true`	Use arrows for multi-line spans
`tab_width`	integer	`4`	Number of spaces per tab
`limit_width`	integer	`0`	Max line width (0 = unlimited)
`ambi_width`	integer	`1`	Width of ambiguous Unicode characters
`label_attach`	string	`"middle"`	Label attachment point (`"start"`, `"middle"`, `"end"`)
`index_type`	string	`"char"`	Position indexing (`"char"` or `"byte"`)
`char_set`	string	`"unicode"`	Glyph set (`"unicode"` or `"ascii"`)
`color`	boolean	`true`	Enable ANSI color codes

Color Generator

local cg = mu.colorgen(min_brightness?)  -- min_brightness ∈ [0, 1], default 0.5
local color_func = cg:next()             -- Get next color in cycle

Architecture

Rendering Pipeline

Report:render()
  ├─ Context Creation (group labels by source, calculate widths)
  ├─ Header Rendering (error level, code, message)
  ├─ For each source group:
  │   ├─ Reference Header (file:line:col)
  │   ├─ Line Rendering:
  │   │   ├─ Label Clustering (group overlapping labels)
  │   │   ├─ Window Calculation (when limit_width > 0)
  │   │   ├─ Virtual Row Splitting (multi-line labels)
  │   │   └─ For each cluster:
  │   │       ├─ Line Content (with label highlighting)
  │   │       └─ Arrow Drawing (underlines, connectors, messages)
  │   └─ Empty Line
  └─ Footer Rendering (notes, help messages)

Key Design Decisions

Intervals:

All position named start/end use half-open intervals [start, end)
All position named first/last use close intervals [fist, last]

Width Caching:

Pre-compute cumulative display widths for each line
Binary search (muC_widthindex) for O(log n) position lookups
Handles UTF-8 multi-byte characters, Emoji, RI, CJK double-width, tabs

Label Clustering:

Group overlapping/nearby labels into virtual rows
Separate inline labels (single line) from multiline labels
Dynamic column range calculation for windowing

Memory Management (C):

Caller provides allocator function (defaults to malloc/free)
Dynamic arrays with geometric growth (muA_* macros)
External pointers (messages, source names) must outlive render call

Testing

Running Tests

# Compile with coverage
gcc -ggdb -shared --coverage -o musubi.so musubi.c

# Run tests (uses C bindings by default)
lua test.lua

# Generate coverage report
lcov -d . -c -o lcov.info
genhtml lcov.info -o coverage/

Test Coverage

Both implementations maintain 100% test coverage:

100 test cases covering all rendering paths
Edge cases: zero-width spans, CJK characters, tab expansion, window truncation
Regression tests for all fixed bugs
Pixel-perfect output verification (2400+ lines of expected output)

Test Categories:

Basic rendering (labels, messages, colors)
Multi-line spans and clustering
Line width limiting and windowing
Unicode and CJK character handling
Configuration options (compact, cross_gap, etc.)
Multi-source file support
File streaming (C only)

Implementation Notes

Differences from Rust Ariadne

Improvements:

Cleaner margin render handling
Explicit virtual row rendering for multi-line labels
Width-based windowing with binary search optimization
Label without message supports

Limitations:

Only supports \n newlines (not Unicode line separators)
Not full UAX#29 grapheme cluster breaking (only support ZWJ & RI now)

C Implementation Details

See .github/c_port.md for detailed implementation notes:

API constraints and call ordering requirements
Memory management and lifetime rules
UTF-8 handling and Unicode width calculations
Source lifecycle and file streaming
Known limitations and edge cases

Project Structure

See .github/project-structure.md for:

Detailed architecture documentation
Data structure definitions
Rendering algorithm explanations
Bug fix history and rationale

Contributing

Contributions are welcome! Please:

Run tests before submitting: lua test.lua
Maintain 100% coverage: Add tests for new features
Follow existing style: Lua uses tabs, C uses 4 spaces
Update documentation: Keep README and .github/*.md in sync

Development Workflow

# Run tests with coverage
lua -lluacov test.lua
luacov ariadne.lua

# Find uncovered lines
grep '^\*\+0 ' luacov.report.out

# Run specific test
lua test.lua TestBasic.test_simple_label

License

MIT License - See LICENSE for details.

Credits

Original Ariadne library: zesterer/ariadne
UTF-8 support: starwing/luautf8
Test framework: LuaUnit

Related Projects

Ariadne (Rust) - Original implementation
Annotate Snippets (Rust) - Similar project
Miette (Rust) - Fancy diagnostics library
Codespan (Rust) - Alternative approach

Made with ❤️ for better compiler diagnostics

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