Expose BuildRecordInfo.computeHash

SwiftPM will compute a hash of the arguments passed to `swift build`,
`swift test`, etc to determine if a full rebuild is necessary.
Currently, it doesn't take in to account whether
`.doesNotAffectIncrementalBuild` is set on swift compiler options and so
any time any compiler option changes it will perform a full rebuild.

Expose the function that swift-driver uses to compute the argument hash
which takes in to account `.doesNotAffectIncrementalBuild` so that
SwiftPM can leverage it to reduce unnecessary rebuilds.

In order to keep `BuildRecordInfo` hidden behind `_spi` the function was
moved out to the standalone `BuildRecordArguments` struct.

Author: plemarquand

Sources/SwiftDriver/IncrementalCompilation/BuildRecordInfo.swift

@@ -97,7 +97,7 @@ import class Dispatch.DispatchQueue
     else {
       return nil
     }
-    let currentArgsHash = Self.computeArgsHash(parsedOptions)
+    let currentArgsHash = BuildRecordArguments.computeHash(parsedOptions)
     let compilationInputModificationDates =
       recordedInputModificationDates.filter { input, _ in
         input.type.isPartOfSwiftCompilation
@@ -113,16 +113,6 @@ import class Dispatch.DispatchQueue
       compilationInputModificationDates: compilationInputModificationDates)
    }
 
-  private static func computeArgsHash(_ parsedOptionsArg: ParsedOptions
-  ) -> String {
-    var parsedOptions = parsedOptionsArg
-    let hashInput = parsedOptions
-      .filter { $0.option.affectsIncrementalBuild && $0.option.kind != .input}
-      .map { $0.description } // The description includes the spelling of the option itself and, if present, its argument(s).
-      .joined()
-    return SHA256().hash(hashInput).hexadecimalRepresentation
-  }
-
   /// Determine the input and output path for the build record
   private static func computeBuildRecordPath(
     outputFileMap: OutputFileMap?,
@@ -209,3 +199,15 @@ import class Dispatch.DispatchQueue
     buildRecordPath.parentDirectory
   }
 }
+
+public struct BuildRecordArguments {
+  /// Compute a hash of the parsed options that affect incremental builds.
+  public static func computeHash(_ parsedOptionsArg: ParsedOptions) -> String {
+    var parsedOptions = parsedOptionsArg
+    let hashInput = parsedOptions
+      .filter { $0.option.affectsIncrementalBuild && $0.option.kind != .input}
+      .map { $0.description } // The description includes the spelling of the option itself and, if present, its argument(s).
+      .joined()
+    return SHA256().hash(hashInput).hexadecimalRepresentation
+  }
+}