Cirrus CI support

source/ci_source/providers/Cirrus.ts

@@ -0,0 +1,32 @@
+import { Env, CISource } from "../ci_source"
+import { ensureEnvKeysExist, ensureEnvKeysAreInt } from "../ci_source_helpers"
+
+export class Travis implements CISource {
+  constructor(private readonly env: Env) {}
+
+  get name(): string {
+    return "Cirrus CI"
+  }
+
+  get isCI(): boolean {
+    return ensureEnvKeysExist(this.env, ["CIRRUS_CI"])
+  }
+
+  get isPR(): boolean {
+    const mustHave = ["CIRRUS_CI", "CIRRUS_PR", "CIRRUS_REPO_FULL_NAME"]
+    const mustBeInts = ["CIRRUS_PR"]
+    return ensureEnvKeysExist(this.env, mustHave) && ensureEnvKeysAreInt(this.env, mustBeInts)
+  }
+
+  get pullRequestID(): string {
+    return this.env.CIRRUS_PR
+  }
+
+  get repoSlug(): string {
+    return this.env.CIRRUS_REPO_FULL_NAME
+  }
+
+  get ciRunURL() {
+    return `https://cirrus-ci.com/task/${this.env.CIRRUS_TASK_ID}`
+  }
+}