Add a macOS pool label only when one is given

.github/workflows/benchmarks.yml

@@ -44,8 +44,8 @@ on:
         default: ""
       macos_runner_pool:
         type: string
-        description: "The self-hosted runner pool for macOS benchmark jobs."
-        default: "general"
+        description: "Label of the pool of self-hosted macOS runners to use, for an organization that splits its runners into pools such as general and nightly. Empty adds no pool label."
+        default: ""
       linux_env_vars:
         type: string
         description: "Environment variables for Linux jobs as JSON."

.github/workflows/package_test.yml

@@ -347,8 +347,8 @@ on:
         default: "ARM64"
       macos_runner_pool:
         type: string
-        description: "macOS self-hosted runner pool label."
-        default: "general"
+        description: "Label of the pool of self-hosted macOS runners to use, for an organization that splits its runners into pools such as general and nightly. Empty adds no pool label."
+        default: ""
       xcode_debug_output:
         type: boolean
         description: "Drop -quiet from the xcodebuild target invocations."

.github/workflows/scripts/matrix/generate-matrix.swift

@@ -71,7 +71,7 @@ struct Configuration {
   @Input("MACOS_SWIFT_VERSIONS") var macOSVersions: [String] = []
   @Input("MACOS_OS") var macOSOS: OSList = "tahoe"
   @Input("MACOS_ARCH") var macOSArchitecture = "ARM64"
-  @Input("MACOS_RUNNER_POOL") var macOSPool = "general"
+  @Input("MACOS_RUNNER_POOL") var macOSPool = ""
   @Input("MACOS_COMMAND") var macOSCommands: Commands = "xcrun swift test"
   @Input("MACOS_SETUP_COMMAND") var macOSSetupCommand = ""
   @Input("MACOS_ENV_VARS") var macOSEnvironment = JSONValue.object([:])
@@ -900,9 +900,12 @@ struct Runner {
     Runner(labels: [label], name: label)
   }
 
-  /// A machine from one of the self-hosted macOS pools.
+  /// A machine from the self-hosted macOS runners, in one of their pools if the organization
+  /// splits them into pools. A pool label no runner carries leaves the job waiting forever,
+  /// so an empty pool adds none.
   static func macOS(os: String, architecture: String, pool: String) -> Runner {
-    Runner(labels: ["self-hosted", "macos", os, architecture, pool], name: os)
+    let poolLabels = pool.isEmpty ? [] : [pool]
+    return Runner(labels: ["self-hosted", "macos", os, architecture] + poolLabels, name: os)
   }
 }
 

.github/workflows/toolchain_matrix.yml

@@ -94,8 +94,8 @@ on:
         default: "ARM64"
       macos_runner_pool:
         type: string
-        description: "macOS self-hosted runner pool label."
-        default: "general"
+        description: "Label of the pool of self-hosted macOS runners to use, for an organization that splits its runners into pools such as general and nightly. Empty adds no pool label."
+        default: ""
       windows_swift_versions:
         type: string
         description: "Windows Swift version list (JSON/YAML array). Empty uses current-2, current-1, current, nightly-release and nightly-main."

tests/MatrixGeneratorValidator/Tests/MatrixGeneratorTests/CoreTests.swift

@@ -127,7 +127,7 @@ struct OSInputTests {
     let macOS = try Generator.run([
       "ENABLE_MACOS": "true", "MACOS_SWIFT_VERSIONS": #"["6.3"]"#, "MACOS_OS": "sequoia",
     ])
-    #expect(macOS.entries.first?.runner == ["self-hosted", "macos", "sequoia", "ARM64", "general"])
+    #expect(macOS.entries.first?.runner == ["self-hosted", "macos", "sequoia", "ARM64"])
 
     let windows = try Generator.run([
       "ENABLE_WINDOWS": "true", "WINDOWS_SWIFT_VERSIONS": #"["6.3"]"#, "WINDOWS_OS": "windows-11-arm",
@@ -150,7 +150,7 @@ struct OSInputTests {
     let macOS = try Generator.run([
       "ENABLE_MACOS": "true", "MACOS_SWIFT_VERSIONS": #"["6.3"]"#, "MACOS_OS": "26.10",
     ])
-    #expect(macOS.entries.first?.runner == ["self-hosted", "macos", "26.10", "ARM64", "general"])
+    #expect(macOS.entries.first?.runner == ["self-hosted", "macos", "26.10", "ARM64"])
   }
 
   @Test("One OS leaves the job names alone, however it is written")
@@ -252,6 +252,18 @@ struct OSInputTests {
     #expect(generated.standardError.contains(#"["jammy""#))
     #expect(!generated.standardError.contains("bad file"))
   }
+
+  @Test("A pool label is added to the runner labels only when one is given")
+  func macOSPoolLabelIsOptional() throws {
+    let environment = ["ENABLE_MACOS": "true", "MACOS_SWIFT_VERSIONS": #"["6.3"]"#, "MACOS_OS": "tahoe"]
+    let without = try Generator.run(environment)
+    #expect(without.entries.first?.runner == ["self-hosted", "macos", "tahoe", "ARM64"])
+
+    var pooled = environment
+    pooled["MACOS_RUNNER_POOL"] = "nightly"
+    let with = try Generator.run(pooled)
+    #expect(with.entries.first?.runner == ["self-hosted", "macos", "tahoe", "ARM64", "nightly"])
+  }
 }
 
 @Suite("Minimum version detection")

tests/MatrixGeneratorValidator/Tests/MatrixGeneratorTests/PlatformTests.swift

@@ -177,7 +177,7 @@ struct MacOSTests {
     let entry = try #require(generated.entries.first)
     #expect(entry.xcodeBuild?.xcodeVersion == "swift_6.3")
     #expect(entry.xcodeBuild?.swiftlyToolchain == "main-snapshot")
-    #expect(entry.runner == ["self-hosted", "macos", "sequoia", "X64", "general"])
+    #expect(entry.runner == ["self-hosted", "macos", "sequoia", "X64"])
     #expect(entry.command == "swiftly run swift build")
   }