[Utility] Add diagnostic data for Process

Author: aciidgh

Sources/Utility/Diagnostics.swift

@@ -167,3 +167,47 @@ public enum PackageLocation {
         }
     }
 }
+
+/// An Swift error enum that can be used as a stub to early exit from a method.
+///
+/// It is not expected for this enum to contain any payload or information about the
+/// error. The actual errors and warnings are supposed to be added using the Diagnostics
+/// engine.
+public enum Diagnostics: Swift.Error {
+    case fatalError
+}
+
+/// Diagnostic for the process execution failure.
+public struct ProcessExecutionError: DiagnosticData {
+    public static let id = DiagnosticID(
+        type: ProcessExecutionError.self,
+        name: "org.swift.diags.process.execution",
+        description: {
+            $0 <<< { "The '" + $0.result.arguments[0] + "' subprocess exited with" }
+            $0 <<< .substitution({
+                let `self` = $0 as! ProcessExecutionError
+                switch self.result.exitStatus {
+                case .terminated(let code):
+                    return "termination code \(code)"
+                case .signalled(let signal):
+                    return "signal \(signal)"
+                }
+            })
+            $0 <<< ".\n"
+
+            $0 <<< "stdout: " <<< .substitution({
+                (try? ($0 as! ProcessExecutionError).result.utf8Output()) ?? ""
+            }) <<< "\n"
+            $0 <<< "stderr: " <<< .substitution({
+                (try? ($0 as! ProcessExecutionError).result.utf8stderrOutput()) ?? ""
+            }) <<< "\n"
+        }
+    )
+
+    /// The process result.
+    public let result: ProcessResult
+
+    public init(_ result: ProcessResult) {
+        self.result = result
+    }
+}

Sources/Utility/Process.swift

@@ -0,0 +1,26 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See http://swift.org/LICENSE.txt for license information
+ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */
+
+import Basic
+
+extension Process {
+    @discardableResult
+    static public func checkNonZeroExit(arguments: [String], environment: [String: String] = env, diagnostics: DiagnosticsEngine) throws -> String {
+        let process = Process(arguments: arguments, environment: environment, redirectOutput: true)
+        try process.launch()
+        let result = try process.waitUntilExit()
+        // Throw if there was a non zero termination.
+        guard result.exitStatus == .terminated(code: 0) else {
+            diagnostics.emit(data: ProcessExecutionError(result))
+            throw Diagnostics.fatalError
+        }
+        return try result.utf8Output()
+    }
+}