Make fresh name generation per file instead of global

This makes the compiler output more stable and avoids overcompilation
during incremental compilation due to context bounds parameters changing
name. This is still not fine-grained enough as noted in the
documentation of CompilationUnit#freshNames.

To work properly, this requires us to always have a compilation unit set
in the context before compiling code, which is a good idea anyway (would
be nice to improve the API to make this harder to screw up).

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

@@ -1,7 +1,7 @@
 package dotty.tools
 package dotc
 
-import util.SourceFile
+import util.{FreshNameCreator, SourceFile}
 import ast.{tpd, untpd}
 import tpd.{Tree, TreeTraverser}
 import typer.PrepareInlineable.InlineAccessors
@@ -27,6 +27,12 @@ class CompilationUnit protected (val source: SourceFile) {
   /** Pickled TASTY binaries, indexed by class. */
   var pickled: Map[ClassSymbol, Array[Byte]] = Map()
 
+  /** The fresh name creator for the current unit.
+   *  FIXME(#7661): This is not fine-grained enough to enable reproducible builds,
+   *  see https://github.com/scala/scala/commit/f50ec3c866263448d803139e119b33afb04ec2bc
+   */
+  val freshNames: FreshNameCreator = new FreshNameCreator.Default
+
   /** Will be set to `true` if contains `Quote`.
    *  The information is used in phase `Staging` in order to avoid traversing trees that need no transformations.
    */

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

@@ -52,7 +52,6 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
       .setTyper(new Typer)
       .addMode(Mode.ImplicitsEnabled)
       .setTyperState(new TyperState(ctx.typerState))
-      .setFreshNames(new FreshNameCreator.Default)
     ctx.initialize()(start) // re-initialize the base context with start
     def addImport(ctx: Context, rootRef: ImportInfo.RootRef) =
       ctx.fresh.setImportInfo(ImportInfo.rootImport(rootRef)(ctx))
@@ -241,12 +240,15 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     }
   }
 
-  def compileFromString(sourceCode: String): Unit = {
-    val virtualFile = new VirtualFile("compileFromString-${java.util.UUID.randomUUID().toString}")
-    val writer = new BufferedWriter(new OutputStreamWriter(virtualFile.output, "UTF-8")) // buffering is still advised by javadoc
-    writer.write(sourceCode)
-    writer.close()
-    compileSources(List(new SourceFile(virtualFile, Codec.UTF8)))
+  def compileFromStrings(sourceCodes: String*): Unit = {
+    val sourceFiles = sourceCodes.map {sourceCode =>
+      val virtualFile = new VirtualFile("compileFromString-${java.util.UUID.randomUUID().toString}")
+      val writer = new BufferedWriter(new OutputStreamWriter(virtualFile.output, "UTF-8")) // buffering is still advised by javadoc
+      writer.write(sourceCode)
+      writer.close()
+      new SourceFile(virtualFile, Codec.UTF8)
+    }
+    compileSources(sourceFiles.toList)
   }
 
   /** Print summary; return # of errors encountered */

compiler/src/dotty/tools/dotc/core/Comments.scala

@@ -121,7 +121,7 @@ object Comments {
         val tree = new Parser(SourceFile.virtual("<usecase>", code)).localDef(codePos.start)
         tree match {
           case tree: untpd.DefDef =>
-            val newName = ctx.freshNames.newName(tree.name, NameKinds.DocArtifactName)
+            val newName = ctx.compilationUnit.freshNames.newName(tree.name, NameKinds.DocArtifactName)
             untpd.cpy.DefDef(tree)(name = newName)
           case _ =>
             ctx.error(ProperDefinitionNotFound(), ctx.source.atSpan(codePos))

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -14,7 +14,7 @@ import Uniques._
 import ast.Trees._
 import ast.untpd
 import Flags.GivenOrImplicit
-import util.{FreshNameCreator, NoSource, SimpleIdentityMap, SourceFile}
+import util.{NoSource, SimpleIdentityMap, SourceFile}
 import typer.{Implicits, ImportInfo, Inliner, NamerContextOps, SearchHistory, SearchRoot, TypeAssigner, Typer, Nullables}
 import Nullables.{NotNullInfo, given}
 import Implicits.ContextualImplicits
@@ -44,12 +44,11 @@ object Contexts {
   private val (sbtCallbackLoc,      store2) = store1.newLocation[AnalysisCallback]()
   private val (printerFnLoc,        store3) = store2.newLocation[Context => Printer](new RefinedPrinter(_))
   private val (settingsStateLoc,    store4) = store3.newLocation[SettingsState]()
-  private val (freshNamesLoc,       store5) = store4.newLocation[FreshNameCreator](new FreshNameCreator.Default)
-  private val (compilationUnitLoc,  store6) = store5.newLocation[CompilationUnit]()
-  private val (runLoc,              store7) = store6.newLocation[Run]()
-  private val (profilerLoc,         store8) = store7.newLocation[Profiler]()
-  private val (notNullInfosLoc,     store9) = store8.newLocation[List[NotNullInfo]]()
-  private val initialStore = store9
+  private val (compilationUnitLoc,  store5) = store4.newLocation[CompilationUnit]()
+  private val (runLoc,              store6) = store5.newLocation[Run]()
+  private val (profilerLoc,         store7) = store6.newLocation[Profiler]()
+  private val (notNullInfosLoc,     store8) = store7.newLocation[List[NotNullInfo]]()
+  private val initialStore = store8
 
   /** The current context */
   def curCtx(given ctx: Context): Context = ctx
@@ -200,9 +199,6 @@ object Contexts {
     /** The current settings values */
     def settingsState: SettingsState = store(settingsStateLoc)
 
-    /** The current fresh name creator */
-    def freshNames: FreshNameCreator = store(freshNamesLoc)
-
     /** The current compilation unit */
     def compilationUnit: CompilationUnit = store(compilationUnitLoc)
 
@@ -471,6 +467,8 @@ object Contexts {
         if (prev != null) prev
         else {
           val newCtx = fresh.setSource(source)
+          if (newCtx.compilationUnit == null)
+            newCtx.setCompilationUnit(CompilationUnit(source))
           sourceCtx = sourceCtx.updated(source, newCtx)
           newCtx
         }
@@ -563,7 +561,6 @@ object Contexts {
     def setSettings(settingsState: SettingsState): this.type = updateStore(settingsStateLoc, settingsState)
     def setRun(run: Run): this.type = updateStore(runLoc, run)
     def setProfiler(profiler: Profiler): this.type = updateStore(profilerLoc, profiler)
-    def setFreshNames(freshNames: FreshNameCreator): this.type = updateStore(freshNamesLoc, freshNames)
     def setNotNullInfos(notNullInfos: List[NotNullInfo]): this.type = updateStore(notNullInfosLoc, notNullInfos)
 
     def setProperty[T](key: Key[T], value: T): this.type =

compiler/src/dotty/tools/dotc/core/NameKinds.scala

@@ -215,7 +215,7 @@ object NameKinds {
 
     /** Generate fresh unique term name of this kind with given prefix name */
     def fresh(prefix: TermName = EmptyTermName)(implicit ctx: Context): TermName =
-      ctx.freshNames.newName(prefix, this)
+      ctx.compilationUnit.freshNames.newName(prefix, this)
 
     /** Generate fresh unique type name of this kind with given prefix name */
     def fresh(prefix: TypeName)(implicit ctx: Context): TypeName =

compiler/test/dotty/tools/DottyTest.scala

@@ -64,7 +64,7 @@ trait DottyTest extends ContextEscapeDetection {
   def checkCompile(checkAfterPhase: String, source: String)(assertion: (tpd.Tree, Context) => Unit): Context = {
     val c = compilerWithChecker(checkAfterPhase)(assertion)
     val run = c.newRun
-    run.compileFromString(source)
+    run.compileFromStrings(source)
     run.runContext
   }
 

compiler/test/dotty/tools/backend/jvm/DottyBytecodeTest.scala

@@ -52,13 +52,13 @@ trait DottyBytecodeTest {
     ctx0.setSetting(ctx0.settings.outputDir, outputDir)
   }
 
-  /** Checks source code from raw string */
-  def checkBCode(source: String)(checkOutput: AbstractFile => Unit): Unit = {
+  /** Checks source code from raw strings */
+  def checkBCode(sources: String*)(checkOutput: AbstractFile => Unit): Unit = {
     implicit val ctx: Context = initCtx
 
     val compiler = new Compiler
     val run = compiler.newRun
-    compiler.newRun.compileFromString(source)
+    compiler.newRun.compileFromStrings(sources: _*)
 
     checkOutput(ctx.settings.outputDir.value)
   }

compiler/test/dotty/tools/backend/jvm/DottyBytecodeTests.scala

@@ -3,6 +3,10 @@ package dotty.tools.backend.jvm
 import org.junit.Assert._
 import org.junit.Test
 
+import scala.tools.asm
+import asm._
+import asm.tree._
+
 import scala.tools.asm.Opcodes
 
 class TestBCode extends DottyBytecodeTest {
@@ -743,4 +747,40 @@ class TestBCode extends DottyBytecodeTest {
       }
     }
   }
+
+  @Test def freshNames = {
+    val sourceA =
+      """|class A {
+         |  def a1[T: Ordering]: Unit = {}
+         |  def a2[T: Ordering]: Unit = {}
+         |}
+      """.stripMargin
+    val sourceB =
+      """|class B {
+         |  def b1[T: Ordering]: Unit = {}
+         |  def b2[T: Ordering]: Unit = {}
+         |}
+      """.stripMargin
+
+    checkBCode(sourceA, sourceB) { dir =>
+      val clsNodeA = loadClassNode(dir.lookupName("A.class", directory = false).input, skipDebugInfo = false)
+      val clsNodeB = loadClassNode(dir.lookupName("B.class", directory = false).input, skipDebugInfo = false)
+      val a1 = getMethod(clsNodeA, "a1")
+      val a2 = getMethod(clsNodeA, "a2")
+      val b1 = getMethod(clsNodeB, "b1")
+      val b2 = getMethod(clsNodeB, "b2")
+
+      def assertParamName(mn: MethodNode, expectedName: String) = {
+        val actualName = mn.localVariables.get(1).name
+        assert(actualName == expectedName,
+          s"Method ${mn.name} has parameter $actualName but expected $expectedName")
+      }
+
+      // The fresh name counter should be reset for every compilation unit
+      assertParamName(a1, "evidence$1")
+      assertParamName(a2, "evidence$2")
+      assertParamName(b1, "evidence$1")
+      assertParamName(b2, "evidence$2")
+    }
+  }
 }

staging/src/scala/quoted/staging/QuoteCompiler.scala

@@ -55,18 +55,20 @@ private class QuoteCompiler extends Compiler {
     override def runOn(units: List[CompilationUnit])(implicit ctx: Context): List[CompilationUnit] =
       units.flatMap {
         case exprUnit: ExprCompilationUnit =>
+          implicit val unitCtx: Context = ctx.fresh.setPhase(this.start).setCompilationUnit(exprUnit)
+
           val pos = Span(0)
           val assocFile = new VirtualFile("<quote>")
 
           // Places the contents of expr in a compilable tree for a class with the following format.
           // `package __root__ { class ' { def apply: Any = <expr> } }`
-          val cls = ctx.newCompleteClassSymbol(defn.RootClass, outputClassName, EmptyFlags,
+          val cls = unitCtx.newCompleteClassSymbol(defn.RootClass, outputClassName, EmptyFlags,
             defn.ObjectType :: Nil, newScope, coord = pos, assocFile = assocFile).entered.asClass
-          cls.enter(ctx.newDefaultConstructor(cls), EmptyScope)
-          val meth = ctx.newSymbol(cls, nme.apply, Method, ExprType(defn.AnyType), coord = pos).entered
+          cls.enter(unitCtx.newDefaultConstructor(cls), EmptyScope)
+          val meth = unitCtx.newSymbol(cls, nme.apply, Method, ExprType(defn.AnyType), coord = pos).entered
 
           val qctx = dotty.tools.dotc.quoted.QuoteContext()
-          val quoted = PickledQuotes.quotedExprToTree(exprUnit.exprBuilder.apply(qctx))(ctx.withOwner(meth))
+          val quoted = PickledQuotes.quotedExprToTree(exprUnit.exprBuilder.apply(qctx))(unitCtx.withOwner(meth))
 
           getLiteral(quoted) match {
             case Some(value) =>