Add hidden --ignore-lock escape hatch (#7338)

This is obviously dangerous, but arguably has been the default behavior
of SwiftPM for many years, so offering an escape hatch seems
appropriate.

Author: neonichu

Sources/CoreCommands/Options.swift

@@ -121,6 +121,9 @@ public struct LocationOptions: ParsableArguments {
         completion: .directory
     )
     public var pkgConfigDirectories: [AbsolutePath] = []
+
+    @Option(name: .customLong("ignore-lock"), help: .hidden)
+    public var ignoreLock: Bool = false
 }
 
 public struct CachingOptions: ParsableArguments {

Sources/CoreCommands/SwiftTool.swift

@@ -913,11 +913,16 @@ public final class SwiftTool {
             try workspaceLock.lock(type: .exclusive, blocking: false)
         } catch let ProcessLockError.unableToAquireLock(errno) {
             if errno == EWOULDBLOCK {
-                self.outputStream.write("Another instance of SwiftPM is already running using '\(self.scratchDirectory)', waiting until that process has finished execution...".utf8)
-                self.outputStream.flush()
-
-                // Only if we fail because there's an existing lock we need to acquire again as blocking.
-                try workspaceLock.lock(type: .exclusive, blocking: true)
+                if self.options.locations.ignoreLock {
+                    self.outputStream.write("Another instance of SwiftPM is already running using '\(self.scratchDirectory)', but this will be ignored since `--ignore-lock` has been passed".utf8)
+                    self.outputStream.flush()
+                } else {
+                    self.outputStream.write("Another instance of SwiftPM is already running using '\(self.scratchDirectory)', waiting until that process has finished execution...".utf8)
+                    self.outputStream.flush()
+
+                    // Only if we fail because there's an existing lock we need to acquire again as blocking.
+                    try workspaceLock.lock(type: .exclusive, blocking: true)
+                }
             }
         }