Fix Bug

Guide for debugging and fixing bugs in Syncpack.

Scientific Debugging Workflow

•Observe — Understand the symptom precisely
•Hypothesise — Form a theory about the root cause
•Experiment — Test the hypothesis with targeted changes
•Validate — Confirm the fix with tests
•Verify — Run full test suite

Step 1: Observe

Gather information before changing code:

bash

# Run the failing test with output
cargo test test_name -- --nocapture

# Run with backtrace
RUST_BACKTRACE=1 cargo test test_name

# Test against fixture
cd fixtures/fluid-framework
cargo run -- lint

Questions to answer:

•What is the exact error message?
•What input triggers it?
•What is the expected vs actual behaviour?

Step 2: Hypothesise

Common root causes by symptom:

Symptom	Likely Cause
State is `Unknown`	`visit_packages` not called or instance skipped
Wrong state assigned	Validation logic order, earlier check overriding
Instance not found	Package/dependency name mismatch, location format
Command not running	Missing registration in cli.rs, main.rs, or commands.rs
Panic/unwrap failure	Unexpected None or Err value

Step 3: Experiment

Add targeted debug output:

rust

use log::debug;

debug!("Instance: {:#?}", instance);
debug!("State before: {:?}", instance.state.borrow());

Search for related code:

bash

# Find where state is assigned
ast-grep -p 'InstanceState::fixable' src/visit_packages/

# Find similar patterns
ast-grep -p 'PATTERN' src/

Step 4: Validate

Write a failing test FIRST (TDD):

rust

#[test]
fn reproduces_the_bug() {
    let ctx = TestBuilder::new()
        .with_packages(vec![/* minimal reproduction */])
        .build_and_visit_packages();

    // Assert expected behaviour (will fail initially)
}

Then fix the code until the test passes.

Step 5: Verify

bash

just test        # All tests pass
cargo clippy     # No warnings

Where to Look

By component

Issue with...	Check...
CLI parsing	`src/cli.rs`
Config loading	`src/config.rs`, `src/rcfile.rs`
Package reading	`src/packages.rs`, `src/package_json.rs`
State assignment	`src/visit_packages/*.rs`
Command output	`src/commands/*.rs`, `src/commands/ui/`
Version parsing	`src/specifier/*.rs`

By phase

Phase	What happens	Files
Create	Read config, packages, collect instances	`context.rs`, `packages.rs`
Inspect	Assign InstanceState	`visit_packages.rs`, `visit_packages/*.rs`
Run	Process instances, output/write	`commands/*.rs`

Common Fixes

Instance state not being assigned

Check:

•Is the instance's version group variant handled in visit_packages.rs?
•Is there an early return skipping this instance?
•Is another validation assigning a state first?

Test assertion failing

Check:

•Is build_and_visit_packages() called (not just build())?
•Is the location string format correct? ("{dep} in {location} of {package}")
•Are there multiple instances of the same dependency?

Command not found

Verify registration in all three places:

•src/cli.rs — Subcommand enum
•src/main.rs — match arm
•src/commands.rs — module declaration

Debugging Tips

•Isolate — Create minimal reproduction
•Binary search — Comment out code to narrow down
•Print early — Add debug output before suspected area
•Check order — Validation order matters (first match wins)
•Read tests — Existing tests show expected behaviour

Anti-Patterns

❌ Changing code without understanding the cause ❌ Removing code just to make tests pass ❌ Fixing symptoms instead of root cause ❌ Skipping the test-first step