throw error if git version is less than 2

Sources/Get/Git.swift

@@ -36,7 +36,12 @@ extension Git {
                 "--depth", "10",
                 url, dstdir, environment: environment, message: "Cloning \(url)")
         } catch POSIX.Error.ExitStatus {
-            throw Error.GitCloneFailure(url, dstdir)
+            // Git 2.0 or higher is required
+            if Git.majorVersionNumber < 2 {
+                throw Utility.Error.ObsoleteGitVersion
+            } else {
+                throw Error.GitCloneFailure(url, dstdir)
+            }
         }
 
         return Repo(path: dstdir)!  //TODO no bangs
@@ -45,7 +50,7 @@ extension Git {
 
 extension Git.Repo {
     var versions: [Version] {
-        let out = (try? popen([Git.tool, "-C", path, "tag", "-l"])) ?? ""
+        let out = (try? Git.runPopen([Git.tool, "-C", path, "tag", "-l"])) ?? ""
         let tags = out.characters.split(separator: Character.newline)
         let versions = tags.flatMap(Version.init).sorted()
         if !versions.isEmpty {
@@ -66,6 +71,6 @@ extension Git.Repo {
      no versions, returns false.
      */
     var versionsArePrefixed: Bool {
-        return (try? popen([Git.tool, "-C", path, "tag", "-l"]))?.hasPrefix("v") ?? false
+        return (try? Git.runPopen([Git.tool, "-C", path, "tag", "-l"]))?.hasPrefix("v") ?? false
     }
 }

Sources/Get/RawClone.swift

@@ -63,8 +63,8 @@ class RawClone: Fetchable {
     func setVersion(ver: Version) throws {
         let packageVersionsArePrefixed = repo.versionsArePrefixed
         let v = (packageVersionsArePrefixed ? "v" : "") + ver.description
-        try popen([Git.tool, "-C", path, "reset", "--hard", v])
-        try popen([Git.tool, "-C", path, "branch", "-m", v])
+        try Git.runPopen([Git.tool, "-C", path, "reset", "--hard", v])
+        try Git.runPopen([Git.tool, "-C", path, "branch", "-m", v])
 
         print("Resolved version:", ver)
 

Sources/Utility/Error.swift

@@ -0,0 +1,25 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright 2015 - 2016 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
+*/
+
+public enum Error: ErrorProtocol {
+    case ObsoleteGitVersion
+    case UnknownGitError
+}
+
+extension Error: CustomStringConvertible {
+    public var description: String {
+        switch self {
+        case ObsoleteGitVersion:
+            return "Git 2.0 or higher is required. Please update git and retry."
+        case UnknownGitError:
+            return "Failed to invoke git command. Please try updating git"
+        }
+    }
+}

Sources/Utility/Git.swift

@@ -10,6 +10,7 @@
 
 import func POSIX.realpath
 import func POSIX.getenv
+import libc
 
 public class Git {
     public class Repo {
@@ -23,7 +24,7 @@ public class Git {
 
         public lazy var origin: String? = { repo in
             do {
-                guard let url = try popen([Git.tool, "-C", repo.path, "config", "--get", "remote.origin.url"]).chuzzle() else {
+                guard let url = try Git.runPopen([Git.tool, "-C", repo.path, "config", "--get", "remote.origin.url"]).chuzzle() else {
                     return nil
                 }
                 if URL.scheme(url) == nil {
@@ -40,15 +41,54 @@ public class Git {
         }(self)
 
         public var branch: String! {
-            return try? popen([Git.tool, "-C", path, "rev-parse", "--abbrev-ref", "HEAD"]).chomp()
+            return try? Git.runPopen([Git.tool, "-C", path, "rev-parse", "--abbrev-ref", "HEAD"]).chomp()
         }
 
         public func fetch() throws {
-            try system(Git.tool, "-C", path, "fetch", "--tags", "origin", message: nil)
+            do {
+                try system(Git.tool, "-C", path, "fetch", "--tags", "origin", message: nil)
+            } catch let errror {
+                Git.handle(errror)
+            }
         }
     }
 
     public class var tool: String {
         return getenv("SWIFT_GIT") ?? "git"
     }
+
+    public class var version: String! {
+        return try? Git.runPopen([Git.tool, "version"])
+    }
+
+    public class var majorVersionNumber: Int? {
+        let prefix = "git version"
+        var version = self.version
+        if version.hasPrefix(prefix) {
+            let prefixRange = version.startIndex...version.startIndex.advanced(by: prefix.characters.count)
+            version.removeSubrange(prefixRange)
+        }
+        guard let first = version.characters.first else {
+            return nil
+        }
+        return Int(String(first))
+    }
+
+    @noreturn public class func handle(error: ErrorProtocol) {
+        // Git 2.0 or higher is required
+        if Git.majorVersionNumber < 2 {
+            print("error: ", Error.ObsoleteGitVersion)
+        } else {
+            print("error: ", Error.UnknownGitError)
+        }
+        exit(1)
+    }
+
+    public class func runPopen(arguments: [String]) throws -> String {
+        do {
+            return try popen(arguments)
+        } catch let error  {
+            handle(error)
+        }
+    }
 }

Tests/LinuxMain.swift

@@ -40,4 +40,5 @@ XCTMain([
     testCase(WalkTests.allTests),
     testCase(ModuleMapsTestCase.allTests),
     testCase(DescribeTests.allTests),
+    testCase(GitUtilityTests.allTests),
 ])

Tests/Utility/GitTests.swift

@@ -0,0 +1,43 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright 2015 - 2016 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
+ */
+
+@testable import Utility
+import XCTest
+
+class GitMoc: Git {
+    static var mocVersion: String = "git version 2.5.4 (Apple Git-61)"
+    override class var version: String! {
+        return mocVersion
+    }
+}
+
+class GitUtilityTests: XCTestCase {
+
+    func testGitVersion() {
+        XCTAssertEqual(GitMoc.majorVersionNumber, 2)
+
+        GitMoc.mocVersion = "2.5.4"
+        XCTAssertEqual(GitMoc.majorVersionNumber, 2)
+
+        GitMoc.mocVersion = "git version 1.5.4"
+        XCTAssertEqual(GitMoc.majorVersionNumber, 1)
+
+        GitMoc.mocVersion = "1.25.4"
+        XCTAssertEqual(GitMoc.majorVersionNumber, 1)
+    }
+}
+
+extension GitUtilityTests {
+    static var allTests : [(String, GitUtilityTests -> () throws -> Void)] {
+        return [
+                   ("testGitVersion", testGitVersion),
+        ]
+    }
+}