Nucleic: Gitea Runner macOS VM Support

Sources/gitea-macos-runner/Main.swift

@@ -136,6 +136,7 @@ final class OnceFlag: @unchecked Sendable {
 final class ProgressPrinter: @unchecked Sendable {
     private let lock = NSLock()
     private var lastLine = ""
+    private var lastGroup: String?
 
     /// Whether carriage-return rewriting means anything here.
     ///
@@ -147,17 +148,31 @@ final class ProgressPrinter: @unchecked Sendable {
     private let isInteractive = isatty(fileno(stderr)) == 1
 
     /// Rewrites the current line.
-    func update(_ line: String) {
+    ///
+    /// - Parameters:
+    ///   - line: The text to show.
+    ///   - group: Names the stage this line belongs to. When it changes, the
+    ///     outgoing stage's final line is sealed with a newline rather than
+    ///     overwritten — so `installing macOS [####] 100%` is still on screen
+    ///     when the operator scrolls back to work out where the last hour went,
+    ///     instead of being replaced by whatever came next.
+    func update(_ line: String, group: String? = nil) {
         lock.lock()
         defer { lock.unlock() }
+
+        if let group, let lastGroup, group != lastGroup, !lastLine.isEmpty, isInteractive {
+            emit("\n")
+            lastLine = ""
+        }
+        if let group { lastGroup = group }
+
         guard line != lastLine else { return }
         lastLine = line
         guard isInteractive else {
-            FileHandle.standardError.write(Data((line + "\n").utf8))
+            emit(line + "\n")
             return
         }
-        let padding = String(repeating: " ", count: max(0, 78 - line.count))
-        FileHandle.standardError.write(Data(("\r" + line + padding).utf8))
+        emit("\r" + line + pad(line))
     }
 
     /// Emits a standalone line without losing the status line under it.
@@ -177,12 +192,20 @@ final class ProgressPrinter: @unchecked Sendable {
         lock.lock()
         defer { lock.unlock() }
         if let line {
-            let padding = isInteractive ? String(repeating: " ", count: max(0, 78 - line.count)) : ""
-            let prefix = isInteractive ? "\r" : ""
-            FileHandle.standardError.write(Data((prefix + line + padding + "\n").utf8))
+            emit((isInteractive ? "\r" : "") + line + (isInteractive ? pad(line) : "") + "\n")
         } else if !lastLine.isEmpty, isInteractive {
-            FileHandle.standardError.write(Data("\n".utf8))
+            emit("\n")
         }
         lastLine = ""
     }
+
+    /// Trailing blanks that erase whatever the previous, longer line left behind.
+    private func pad(_ line: String) -> String {
+        String(repeating: " ", count: max(0, 78 - line.count))
+    }
+
+    /// Writes straight to the descriptor. Call with ``lock`` held.
+    private func emit(_ text: String) {
+        FileHandle.standardError.write(Data(text.utf8))
+    }
 }