Refinements to Diagnostics type based on SE-0303 amendment review modifications.

Mark the Severity as public and add a method that takes it as a parameter.

Author: abertelrud

Sources/PackagePlugin/Implementation.swift

@@ -102,10 +102,7 @@ struct PrebuildCommand: Encodable {
 }
 
 struct Diagnostic: Encodable {
-    enum Severity: String, Encodable {
-        case error, warning, remark
-    }
-    let severity: Severity
+    let severity: Diagnostics.Severity
     let message: String
     let file: Path?
     let line: Int?

Sources/PackagePlugin/PublicAPI/Diagnostics.swift

@@ -11,22 +11,32 @@
 /// Emits errors, warnings, and remarks to be shown as a result of running the
 /// plugin. After emitting one or more errors, the plugin should return a
 /// non-zero exit code.
-public final class Diagnostics {
+public struct Diagnostics {
 
     // This prevents a Diagnostics from being instantiated by the script.
     internal init() {}
+    
+    /// Severity of the diagnostic.
+    public enum Severity: String, Encodable {
+        case error, warning, remark
+    }
+
+    /// Emits an error with a specified severity and message, and optional file path and line number.
+    public static func emit(_ severity: Severity, _ message: String, file: Path? = #file, line: Int? = #line) {
+        output.diagnostics.append(Diagnostic(severity: severity, message: message, file: file, line: line))
+    }
 
-    /// Emits an error with the specified message and optional file path and line number..
+    /// Emits an error with the specified message, and optional file path and line number.
     public static func error(_ message: String, file: Path? = nil, line: Int? = nil) {
         output.diagnostics.append(Diagnostic(severity: .error, message: message, file: file, line: line))
     }
 
-    /// Emits a warning with the specified message and optional file path and line number..
+    /// Emits a warning with the specified message, and optional file path and line number.
     public static func warning(_ message: String, file: Path? = nil, line: Int? = nil) {
         output.diagnostics.append(Diagnostic(severity: .warning, message: message, file: file, line: line))
     }
 
-    /// Emits a remark with the specified message and optional file path and line number..
+    /// Emits a remark with the specified message, and optional file path and line number.
     public static func remark(_ message: String, file: Path? = nil, line: Int? = nil) {
         output.diagnostics.append(Diagnostic(severity: .remark, message: message, file: file, line: line))
     }