[swift-snapshot-tool] Make computing the branch name part of the download url more flexible so it works for release branches.

utils/swift_snapshot_tool/Sources/swift_snapshot_tool/download_toolchain.swift

@@ -128,7 +128,7 @@ func downloadToolchainAndRunTest(
   let fileType = platform.fileType
   let toolchainType = platform.toolchainType
 
-  let realBranch = branch != .development ? "swift-\(branch)-branch" : branch.rawValue
+  let realBranch = branch.urlBranchName
   let toolchainDir = "\(workspace)/\(tag.name)-\(platform)"
   let downloadPath = URL(fileURLWithPath: "\(workspace)/\(tag.name)-\(platform).\(fileType)")
   if !fileExists(toolchainDir) {

utils/swift_snapshot_tool/Sources/swift_snapshot_tool/get_tags.swift

@@ -27,18 +27,23 @@ struct Tag: Decodable {
     ref.dropFirst(10)
   }
 
-  func dateString(_ branch: Branch) -> Substring {
-    // FIXME: If we ever actually use interesting a-b builds, we should capture this information
-    // would be better to do it sooner than later.
-    return name.dropFirst("swift-".count + branch.rawValue.count + "-SNAPSHOT-".count).dropLast(2)
-  }
-
   func date(branch: Branch) -> Date {
-    // TODO: I think that d might be a class... if so, we really want to memoize
-    // this.
     let d = DateFormatter()
     d.dateFormat = "yyyy-MM-dd"
-    return d.date(from: String(dateString(branch)))!
+    // TODO: Change top use swift regexp
+    let pattern = "swift-.*DEVELOPMENT-SNAPSHOT-(\\d+-\\d+-\\d+)"
+    do {
+      let regex = try NSRegularExpression(pattern: pattern, options: .caseInsensitive)
+      guard let match = regex.firstMatch(in: String(name),
+                                         options: [],
+                                         range: NSRange(location: 0, length: name.utf16.count)) else {
+        fatalError("Failed to find match!")
+      }
+      let str = String((name as NSString).substring(with: match.range(at: 1)))
+      return d.date(from: str)!
+    } catch let error as NSError {
+      fatalError("Error creating NSRegularExpression: \(error)")
+    }
   }
 }
 

utils/swift_snapshot_tool/Sources/swift_snapshot_tool/github_repository.swift

@@ -23,8 +23,8 @@ enum Platform: String, EnumerableFlag {
     case .osx:
       return "pkg"
     case .ubuntu1404,
-      .ubuntu1604,
-      .ubuntu1804:
+         .ubuntu1604,
+         .ubuntu1804:
       return "tar.gz"
     }
   }
@@ -34,8 +34,8 @@ enum Platform: String, EnumerableFlag {
     case .osx:
       return "xcode"
     case .ubuntu1404,
-      .ubuntu1604,
-      .ubuntu1804:
+         .ubuntu1604,
+         .ubuntu1804:
       return self.rawValue
     }
   }
@@ -50,9 +50,18 @@ enum Branch: String, EnumerableFlag {
   var tagPrefix: String {
     switch self {
     case .development:
-       "swift-\(rawValue.uppercased())"
+      "swift-\(rawValue.uppercased())"
     default:
-       "swift-\(rawValue.uppercased())-DEVELOPMENT"
+      "swift-\(rawValue.uppercased())-DEVELOPMENT"
+    }
+  }
+
+  var urlBranchName: String {
+    switch self {
+    case .development:
+      return self.rawValue
+    default:
+      return "swift-\(self.rawValue)-branch"
     }
   }
 }