Allow tasty files to be the input of -from-tasty

Also works for -decompile and any other compiler that has the -form-tatsy flag.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/Driver.scala

@@ -1,13 +1,16 @@
 package dotty.tools.dotc
 
+import java.nio.file.{Files, Paths}
+
 import dotty.tools.FatalError
 import config.CompilerCommand
 import core.Comments.{ContextDoc, ContextDocstrings}
 import core.Contexts.{Context, ContextBase}
 import core.Mode
 import reporting._
+
 import scala.util.control.NonFatal
-import fromtasty.TASTYCompiler
+import fromtasty.{TASTYCompiler, TastyFileUtil}
 
 /** Run the Dotty compiler.
  *
@@ -132,7 +135,24 @@ class Driver {
    *                    if compilation succeeded.
    */
   def process(args: Array[String], rootCtx: Context): Reporter = {
-    val (fileNames, ctx) = setup(args, rootCtx)
+    val (fileNames0, ctx0) = setup(args, rootCtx)
+    val (fileNames, ctx) =
+      if (ctx0.settings.fromTasty.value(ctx0)) {
+        // Resolve classpath and class names of tasty files
+        val (classPaths, classNames) = fileNames0.map { name =>
+          val path = Paths.get(name)
+          if (!name.endsWith(".tasty")) ("", name)
+          else if (Files.exists(path)) TastyFileUtil.getClassName(path)
+          else {
+            ctx0.error(s"File $name does not exist.")
+            ("", name)
+          }
+        }.unzip
+        val ctx1 = ctx0.fresh
+        val classPaths1 = classPaths.distinct.filter(_ != "")
+        ctx1.setSetting(ctx1.settings.classpath, (ctx1.settings.classpath.value(ctx1) :: classPaths1).mkString(":"))
+        (classNames, ctx1)
+      } else (fileNames0, ctx0)
     doCompile(newCompiler(ctx), fileNames)(ctx)
   }
 

compiler/src/dotty/tools/dotc/fromtasty/TastyFileUtil.scala

@@ -0,0 +1,39 @@
+package dotty.tools.dotc.fromtasty
+
+import java.nio.file.{Files, Path, Paths}
+
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.NameKinds
+import dotty.tools.dotc.core.Names.SimpleName
+import dotty.tools.dotc.core.StdNames.nme
+import dotty.tools.dotc.core.tasty.TastyUnpickler
+
+object TastyFileUtil {
+
+  /** Get the class path and the class name including packages
+   *
+   *  If
+   *  ```scala
+   *    package foo
+   *    class Foo
+   *  ```
+   *  then `getClassName("./out/foo/Foo.tasty") returns `("./out", "foo.Foo")`
+   */
+  def getClassName(path: Path): (String, String) = {
+    assert(path.toString.endsWith(".tasty"))
+    assert(Files.exists(path))
+    val bytes = Files.readAllBytes(path)
+    val unpickler: TastyUnpickler = new TastyUnpickler(bytes)
+    val className =
+      unpickler.nameAtRef.contents.iterator.takeWhile {
+        case name: SimpleName => name != nme.CONSTRUCTOR
+        case name => !name.is(NameKinds.ModuleClassName)
+      }.collect {
+        case name: SimpleName => name.toString
+      }.drop(1).toList
+
+    val classpath = path.toString.replace(className.mkString("", "/", ".tasty"), "")
+    (classpath, className.mkString("."))
+  }
+
+}