Make separation checking controlled by language import

It's import language.experimental.separationChecking

Author: odersky

compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala

@@ -259,7 +259,10 @@ class CheckCaptures extends Recheck, SymTransformer:
  /** The set of symbols that were rechecked via a completer */
  private val completed = new mutable.HashSet[Symbol]
 
- var needAnotherRun = false
+ /** Set on recheckClassDef since there we see all language imports */
+ private var sepChecksEnabled = false
+
+ private var needAnotherRun = false
 
  def resetIteration()(using Context): Unit =
  needAnotherRun = false
@@ -511,7 +514,7 @@ class CheckCaptures extends Recheck, SymTransformer:
  // The path-use.scala neg test contains an example.
  val underlying = CaptureSet.ofTypeDeeply(c1.widen)
  capt.println(i"Widen reach $c to $underlying in ${env.owner}")
- if ccConfig.useSepChecks then
+ if sepChecksEnabled then
  recur(underlying.filter(!_.isTerminalCapability), env, null)
  // we don't want to disallow underlying Fresh instances, since these are typically locally created
  // fresh capabilities. We don't need to also follow the hidden set since separation
@@ -1144,6 +1147,7 @@ class CheckCaptures extends Recheck, SymTransformer:
  * is already done in the TypeApply.
  */
  override def recheckClassDef(tree: TypeDef, impl: Template, cls: ClassSymbol)(using Context): Type =
+ if Feature.enabled(Feature.separationChecking) then sepChecksEnabled = true
  val localSet = capturedVars(cls)
  for parent <- impl.parents do // (1)
  checkSubset(capturedVars(parent.tpe.classSymbol), localSet, parent.srcPos,
@@ -2014,7 +2018,7 @@ class CheckCaptures extends Recheck, SymTransformer:
  end checker
 
  checker.traverse(unit)(using ctx.withOwner(defn.RootClass))
- if ccConfig.useSepChecks then SepCheck(this).traverse(unit)
+ if sepChecksEnabled then SepCheck(this).traverse(unit)
  if !ctx.reporter.errorsReported then
  // We dont report errors here if previous errors were reported, because other
  // errors often result in bad applied types, but flagging these bad types gives

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -32,6 +32,7 @@ object Feature:
  val saferExceptions = experimental("saferExceptions")
  val pureFunctions = experimental("pureFunctions")
  val captureChecking = experimental("captureChecking")
+ val separationChecking = experimental("separationChecking")
  val into = experimental("into")
  val modularity = experimental("modularity")
  val quotedPatternsWithPolymorphicFunctions = experimental("quotedPatternsWithPolymorphicFunctions")
@@ -60,6 +61,7 @@ object Feature:
  (saferExceptions, "Enable safer exceptions"),
  (pureFunctions, "Enable pure functions for capture checking"),
  (captureChecking, "Enable experimental capture checking"),
+ (separationChecking, "Enable experimental separation checking (requires captureChecking)"),
  (into, "Allow into modifier on parameter types"),
  (modularity, "Enable experimental modularity features"),
  (packageObjectValues, "Enable experimental package objects as values"),

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -37,7 +37,7 @@ class CompilationTests {
  compileFilesInDir("tests/pos-special/sourcepath/outer", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
  compileFile("tests/pos-special/sourcepath/outer/nested/Test4.scala", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
  compileFilesInDir("tests/pos-scala2", defaultOptions.and("-source", "3.0-migration")),
- compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
+ compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-language:experimental.separationChecking")),
  compileFile("tests/pos-special/utf8encoded.scala", defaultOptions.and("-encoding", "UTF8")),
  compileFile("tests/pos-special/utf16encoded.scala", defaultOptions.and("-encoding", "UTF16")),
  compileDir("tests/pos-special/i18589", defaultOptions.and("-Wsafe-init").without("-Ycheck:all")),
@@ -149,7 +149,7 @@ class CompilationTests {
  aggregateTests(
  compileFilesInDir("tests/neg", defaultOptions, FileFilter.exclude(TestSources.negScala2LibraryTastyExcludelisted)),
  compileFilesInDir("tests/neg-deep-subtype", allowDeepSubtypes),
- compileFilesInDir("tests/neg-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
+ compileFilesInDir("tests/neg-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-language:experimental.separationChecking")),
  compileFile("tests/neg-custom-args/sourcepath/outer/nested/Test1.scala", defaultOptions.and("-sourcepath", "tests/neg-custom-args/sourcepath")),
  compileDir("tests/neg-custom-args/sourcepath2/hi", defaultOptions.and("-sourcepath", "tests/neg-custom-args/sourcepath2", "-Xfatal-warnings")),
  compileList("duplicate source", List(
@@ -172,7 +172,7 @@ class CompilationTests {
  aggregateTests(
  compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init")),
  compileFilesInDir("tests/run-deep-subtype", allowDeepSubtypes),
- compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking", "-source", "3.8")),
+ compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking", "-language:experimental.separationChecking")),
  // Run tests for legacy lazy vals.
  compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
  ).checkRuns()

library/src/scala/runtime/stdLibPatches/language.scala

@@ -84,6 +84,13 @@ object language:
  @compileTimeOnly("`captureChecking` can only be used at compile time in import statements")
  object captureChecking
 
+ /** Experimental support for separation checking; requires captureChecking also to be enabled.
+ *
+ * @see [[https://dotty.epfl.ch/docs/reference/experimental/cc]]
+ */
+ @compileTimeOnly("`separationChecking` can only be used at compile time in import statements")
+ object separationChecking
+
  /** Experimental support for automatic conversions of arguments, without requiring
  * a language import `import scala.language.implicitConversions`.
  *

project/Build.scala

@@ -1512,7 +1512,7 @@ object Build {
  settings(scala2LibraryBootstrappedSettings).
  settings(
  moduleName := "scala2-library-cc",
- scalacOptions ++= Seq("-source", "3.8"), // for separation checking
+ scalacOptions += "-language:experimental.separationChecking" // for separation checking
  )
 
  lazy val scala2LibraryBootstrappedSettings = Seq(

tests/neg-custom-args/captures/capture-vars-subtyping.scala renamed to tests/neg/capture-vars-subtyping.scala

@@ -1,5 +1,5 @@
 import language.experimental.captureChecking
-import language.`3.7` // no separation checking, TODO enable
+// no separation checking, TODO enable and move to neg-customargs
 import caps.*
 
 def test[C^] =

tests/neg-custom-args/captures/cc-fresh-levels.scala renamed to tests/neg/cc-fresh-levels.scala

@@ -1,5 +1,5 @@
-//> using options -source 3.7
 import language.experimental.captureChecking
+// no separation checking
 import caps.*
 class IO
 class Ref[X](init: X):