Visual Studio Code – Is there a way to see if a file is source controlled and get its GitHub repo URL?

Try this code. It gets the workspace folder of the file you are interested in. And then checks if that is one of the git repositories that you have opened – it works for single root or multiroot workspaces where a file may be in a root folder that may or may not be in a git repo.

    const gitExtension = vscode.extensions.getExtension('vscode.git').exports;
    const api = gitExtension.getAPI(1);

    // some file you are interested in, get a uri from it
    // note forward slashes
    const myUri = vscode.Uri.file('C:/Users/Mark/OneDrive/TestMultiRoot/Test.js');

    // note double backslashes also work
    // const myUri = vscode.Uri.file('C:\Users\Mark\OneDrive\TestMultiRoot\Test.js');

    // below single backslashes - DO NOT WORK
    // const myUri = vscode.Uri.file('C:UsersMarkOneDrivecommand-aliasscratchpad.txt');

    const repo = api.repositories.find(repo => {
        // to test current editor, below returns the workspaceFolder
        // const inThisFolder = vscode.workspace.getWorkspaceFolder(vscode.window.activeTextEditor.document.uri);
        
        const inThisFolder = vscode.workspace.getWorkspaceFolder(myUri);
        return inThisFolder?.uri?.fsPath === repo?.rootUri?.fsPath;
    });

    if (!repo) return;  // no git repo for this file
    const repoPath = repo.repository.remotes[0].fetchUrl;
    // repoPath is like "https://github.com/ArturoDent/command-alias.git"

    // note that 'remotes' is an array, it will contain CLONES of the original repository
    // but it appears that remotes[0] is the current working repository you are interested in, check

See also https://stackoverflow.com/a/59442538 and Git integration for Visual Studio Code especially the part about extensionDependencies.