Add get_relative_path() to base filesystem methods

[gui-marc]

Feature Description

This PR introduces the get_relative_path function, which computes the relative path from a given base path to a specified file. The function signature is as follows:

std::string get_relative_path(const std::string& filename, const std::string& base_path);

Functionality

The get_relative_path function takes two parameters:

• filename: The absolute path of the target file.
• base_path: The absolute path of the base directory.

The function returns a string representing the relative path from base_path to filename. This is useful in scenarios where relative paths are needed for portability, readability, or other path manipulations.

Usage Examples

Below are some examples demonstrating how to use the get_relative_path function:

std::string filename = "/home/user/projects/my_project/src/main.cpp";
std::string base_path = "/home/user/projects/my_project";

std::string relative_path = get_relative_path(filename, base_path);

// Output: "src/main.cpp"

std::string filename = "/var/www/html/index.html";
std::string base_path = "/var/www/xpto";

std::string relative_path = get_relative_path(filename, base_path);

// Output: "../html/index.html"

Testing

Comprehensive tests have been added to ensure the correctness of the get_relative_path function. The tests cover various scenarios, including:

• Standard use cases with different base and target paths.
• Edge cases where the paths are identical.
• Cases with paths involving different directory levels.

Related to aseprite/aseprite#4389

I agree that my contributions are licensed under the MIT License.
You can find a copy of this license at https://opensource.org/licenses/MIT

[aseprite-bot]

clang-tidy review says "All clean, LGTM! 👍"

[dacap]

Thanks @gui-marc for this, just some minor changes requested.

[aseprite-bot]

clang-tidy review says "All clean, LGTM! 👍"

[dacap]

Thanks for the PR and the fixes @gui-marc 👍