add BranchError and BranchErrorReason

src/env/node/git/git.ts

@@ -74,6 +74,10 @@ const textDecoder = new TextDecoder('utf8');
 const rootSha = '4b825dc642cb6eb9a060e54bf8d69288fbee4904';
 
 export const GitErrors = {
+	noRemoteReference: /unable to delete '.+?': remote ref does not exist/i,
+	invalidBranchName: /fatal: '.+?' is not a valid branch name/i,
+	branchAlreadyExists: /fatal: A branch named '.+?' already exists/i,
+	branchNotFullyMerged: /error: The branch '.+?' is not fully merged/i,
 	badRevision: /bad revision '(.*?)'/i,
 	cantLockRef: /cannot lock ref|unable to update local ref/i,
 	changesWouldBeOverwritten: /Your local changes to the following files would be overwritten/i,
@@ -509,7 +513,34 @@ export class Git {
 	}
 
 	async branch(repoPath: string, ...args: string[]): Promise<void> {
-		return this.git<string>({ cwd: repoPath }, 'branch', ...args);
+		try {
+			await this.git<string>({ cwd: repoPath }, 'branch', ...args);
+		} catch (ex) {
+			const msg: string = ex?.toString() ?? '';
+			let reason: BranchErrorReason = BranchErrorReason.Other;
+			switch (true) {
+				case GitErrors.noRemoteReference.test(msg) || GitErrors.noRemoteReference.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.NoRemoteReference;
+					break;
+				case GitErrors.invalidBranchName.test(msg) || GitErrors.invalidBranchName.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.InvalidBranchName;
+					break;
+				case GitErrors.branchAlreadyExists.test(msg) || GitErrors.branchAlreadyExists.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.BranchAlreadyExists;
+					break;
+				case GitErrors.branchNotFullyMerged.test(msg) || GitErrors.branchNotFullyMerged.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.BranchNotFullyMerged;
+					break;
+				case GitErrors.branchNotYetBorn.test(msg) || GitErrors.branchNotYetBorn.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.BranchNotYetBorn;
+					break;
+				case GitErrors.branchFastForwardRejected.test(msg) ||
+					GitErrors.branchFastForwardRejected.test(ex.stderr ?? ''):
+					reason = BranchErrorReason.BranchFastForwardRejected;
+					break;
+			}
+			throw new BranchError(reason, ex);
+		}
 	}
 
 	branch__set_upstream(repoPath: string, branch: string, remote: string, remoteBranch: string) {

src/git/errors.ts

@@ -218,6 +218,60 @@ export class PushError extends Error {
 	}
 }
 
+export const enum BranchErrorReason {
+	BranchAlreadyExists,
+	BranchNotFullyMerged,
+	NoRemoteReference,
+	InvalidBranchName,
+	Other,
+}
+
+export class BranchError extends Error {
+	static is(ex: unknown, reason?: BranchErrorReason): ex is BranchError {
+		return ex instanceof BranchError && (reason == null || ex.reason === reason);
+	}
+
+	readonly original?: Error;
+	readonly reason: BranchErrorReason | undefined;
+
+	constructor(reason?: BranchErrorReason, original?: Error, branch?: string);
+	constructor(message?: string, original?: Error);
+	constructor(messageOrReason: string | BranchErrorReason | undefined, original?: Error, branch?: string) {
+		let message;
+		const baseMessage = `Unable to perform action on branch${branch ? ` '${branch}'` : ''}`;
+		let reason: BranchErrorReason | undefined;
+		if (messageOrReason == null) {
+			message = baseMessage;
+		} else if (typeof messageOrReason === 'string') {
+			message = messageOrReason;
+			reason = undefined;
+		} else {
+			reason = messageOrReason;
+			switch (reason) {
+				case BranchErrorReason.BranchAlreadyExists:
+					message = `${baseMessage} because it already exists.`;
+					break;
+				case BranchErrorReason.BranchNotFullyMerged:
+					message = `${baseMessage} because it is not fully merged.`;
+					break;
+				case BranchErrorReason.NoRemoteReference:
+					message = `${baseMessage} because the remote reference does not exist.`;
+					break;
+				case BranchErrorReason.InvalidBranchName:
+					message = `${baseMessage} because the branch name is invalid.`;
+					break;
+				default:
+					message = baseMessage;
+			}
+		}
+		super(message);
+
+		this.original = original;
+		this.reason = reason;
+		Error.captureStackTrace?.(this, BranchError);
+	}
+}
+
 export const enum PullErrorReason {
 	Conflict,
 	GitIdentity,