Add quiet flag (-q, --quiet) to LoggingOptions. (#5988)

* Add quiet flag (-q, --quiet) to LoggingOptions.

Author: clayellis

Sources/CoreCommands/Options.swift

@@ -138,6 +138,10 @@ public struct LoggingOptions: ParsableArguments {
     /// The verbosity of informational output.
     @Flag(name: [.long, .customLong("vv")], help: "Increase verbosity to include debug output")
     public var veryVerbose: Bool = false
+
+    /// Whether logging output should be limited to `.error`.
+    @Flag(name: .shortAndLong, help: "Decrease verbosity to only include error output.")
+    public var quiet: Bool = false
 }
 
 public struct SecurityOptions: ParsableArguments {

Sources/CoreCommands/SwiftTool.swift

@@ -822,6 +822,8 @@ extension LoggingOptions {
             return .info
         } else if self.veryVerbose {
             return .debug
+        } else if self.quiet {
+            return .error
         } else {
             return .warning
         }

Tests/CommandsTests/SwiftToolTests.swift

@@ -115,6 +115,44 @@ final class SwiftToolTests: CommandsTestCase {
                 XCTAssertMatch(outputStream.bytes.validDescription, .contains("info: info"))
                 XCTAssertMatch(outputStream.bytes.validDescription, .contains("debug: debug"))
             }
+
+            do {
+                let outputStream = BufferedOutputByteStream()
+                let options = try GlobalOptions.parse(["--package-path", fixturePath.pathString, "--quiet"])
+                let tool = try SwiftTool.createSwiftToolForTest(outputStream: outputStream, options: options)
+                XCTAssertEqual(tool.logLevel, .error)
+
+                tool.observabilityScope.emit(error: "error")
+                tool.observabilityScope.emit(warning: "warning")
+                tool.observabilityScope.emit(info: "info")
+                tool.observabilityScope.emit(debug: "debug")
+
+                tool.waitForObservabilityEvents(timeout: .now() + .seconds(1))
+
+                XCTAssertMatch(outputStream.bytes.validDescription, .contains("error: error"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("warning: warning"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("info: info"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("debug: debug"))
+            }
+
+            do {
+                let outputStream = BufferedOutputByteStream()
+                let options = try GlobalOptions.parse(["--package-path", fixturePath.pathString, "-q"])
+                let tool = try SwiftTool.createSwiftToolForTest(outputStream: outputStream, options: options)
+                XCTAssertEqual(tool.logLevel, .error)
+
+                tool.observabilityScope.emit(error: "error")
+                tool.observabilityScope.emit(warning: "warning")
+                tool.observabilityScope.emit(info: "info")
+                tool.observabilityScope.emit(debug: "debug")
+
+                tool.waitForObservabilityEvents(timeout: .now() + .seconds(1))
+
+                XCTAssertMatch(outputStream.bytes.validDescription, .contains("error: error"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("warning: warning"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("info: info"))
+                XCTAssertNoMatch(outputStream.bytes.validDescription, .contains("debug: debug"))
+            }
         }
     }