Fix library usage

[yoheimuta]

This pull request refactors the protolint codebase to improve modularity by introducing a new libinternal package and updating the usage of linting functionality across the project. It also includes changes to streamline testing and enhance error handling. Below is a summary of the most important changes:

Refactoring for Modularity

• Introduced a new libinternal package to encapsulate core linting logic, including the Lint function, LintRunner interface, and error definitions (ErrLintFailure and ErrInternalFailure). This improves separation of concerns and reduces coupling between internal components (internal/libinternal/lint.go).
• Updated the lib package to delegate linting logic to libinternal, simplifying its implementation. The lib.Lint function now auto-initializes the default runner if none is set (lib/lint.go). [1] [2]

Code Adjustments for Refactoring

• Replaced direct usage of the lib package with libinternal in various files, such as cmd/lint_runner.go and mcp/tools.go, to align with the new modular structure. This includes changes to function calls and error handling (internal/cmd/lint_runner.go, mcp/tools.go). [1] [2] [3] [4]

Testing Enhancements

• Refactored the mock implementation of LintRunner into a separate test package (lib_test) and introduced a NewMockLintRunner function for cleaner test setup. This ensures the original runner is restored after tests (lib/mock_lint_runner_test.go). [1] [2]
• Updated lib/lint_test.go to use the new NewMockLintRunner function for testing, ensuring isolation and maintainability of test cases.

Documentation Updates

• Updated the README.md file to include a more comprehensive example of using protolint from Go code, demonstrating error handling and output processing (README.md).

[Copilot]

Pull Request Overview

This PR refactors the protolint codebase to improve modularity by introducing a new libinternal package to encapsulate core linting functionality and update related usages across the project. Key changes include:

• Redirecting the linting functionality from the lib package to the new libinternal package in production and test code.
• Refactoring the test setup to use a dedicated NewMockLintRunner function.
• Updating the documentation to reflect these internal changes.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
mcp/tools.go	Updated import and error handling to use libinternal.
lib/mock_lint_runner_test.go	Changed package and replaced init() with NewMockLintRunner.
lib/lint_test.go	Updated test setup to use the new NewMockLintRunner function.
lib/lint.go	Delegated default runner management to libinternal with auto-init.
internal/libinternal/lint.go	Introduced new core linting functionality encapsulated in libinternal.
internal/cmd/lint_runner.go	Updated runner initialization to use libinternal's runner setter.
README.md	Adjusted usage examples to reflect new modular changes.

[Copilot]

[nitpick] Consider caching the initialized runner in a local variable after calling cmd.Initialize() to avoid potentially re-evaluating the nil check on subsequent Lint calls.

Suggested change

	if libinternal.GetLintRunner() == nil {
	cmd.Initialize()
	runner := libinternal.GetLintRunner()
	if runner == nil {
	cmd.Initialize()
	runner = libinternal.GetLintRunner()