reduce file-io in extractDependencies

Author: bishabosha

compiler/src/dotty/tools/dotc/classpath/FileUtils.scala

@@ -20,6 +20,10 @@ object FileUtils {
     def isClass: Boolean = !file.isDirectory && file.hasExtension("class") && !file.name.endsWith("$class.class")
       // FIXME: drop last condition when we stop being compatible with Scala 2.11
 
+    def isClassExtension: Boolean = file.hasExtension("class")
+
+    def isTastyExtension: Boolean = file.hasExtension("tasty")
+
     def isTasty: Boolean = !file.isDirectory && file.hasExtension("tasty")
 
     def isScalaBinary: Boolean = file.isClass || file.isTasty

compiler/src/dotty/tools/dotc/sbt/ExtractDependencies.scala

@@ -7,7 +7,7 @@ import java.io.File
 import java.util.{Arrays, EnumSet}
 
 import dotty.tools.dotc.ast.tpd
-import dotty.tools.dotc.classpath.FileUtils.{isTasty, isClass}
+import dotty.tools.dotc.classpath.FileUtils.{isTasty, isClassExtension, isTastyExtension}
 import dotty.tools.dotc.core.Contexts._
 import dotty.tools.dotc.core.Decorators._
 import dotty.tools.dotc.core.Flags._
@@ -142,13 +142,16 @@ class ExtractDependencies extends Phase {
     if (depFile != null) {
       // Cannot ignore inheritance relationship coming from the same source (see sbt/zinc#417)
       def allowLocal = dep.context == DependencyByInheritance || dep.context == LocalDependencyByInheritance
-      val depClassFile =
-        if depFile.isClass then depFile
-        else depFile.resolveSibling(dep.to.binaryClassName + ".class")
-      if (depClassFile != null) {
-        // Dependency is external -- source is undefined
-        processExternalDependency(depClassFile, dep.to.binaryClassName)
-      } else if (allowLocal || depFile.file != sourceFile) {
+      if depFile.isTastyExtension then
+        val depClassFile = depFile.resolveSibling(depFile.name.stripSuffix(".tasty") + ".class")
+        if depClassFile != null then
+          // did not find associated class file, e.g. for a TASTy-only classpath.
+          // The file that Zinc recieves with binaryDependency is used to lookup any either any
+          // generated non-local classes or produced xsbti.API associated with the file.
+          processExternalDependency(depClassFile, dep.to.binaryClassName)
+      else if depFile.isClassExtension then
+        processExternalDependency(depFile, dep.to.binaryClassName)
+      else if (allowLocal || depFile.file != sourceFile) {
         // We cannot ignore dependencies coming from the same source file because
         // the dependency info needs to propagate. See source-dependencies/trait-trait-211.
         val toClassName = classNameAsString(dep.to)

compiler/src/dotty/tools/io/PlainFile.scala

@@ -102,8 +102,15 @@ class PlainFile(val givenPath: Path) extends AbstractFile {
    */
   def lookupName(name: String, directory: Boolean): AbstractFile = {
     val child = givenPath / name
-    if ((child.isDirectory && directory) || (child.isFile && !directory)) new PlainFile(child)
-    else null
+    if directory then
+      if child.isDirectory /* IO! */ then
+        new PlainFile(child)
+      else
+        null
+    else if child.isFile /* IO! */ then
+      new PlainFile(child)
+    else
+      null
   }
 
   /** Does this abstract file denote an existing file? */