Move separation checking to -source:3.8 (#23249)

Raise separation checking guard to `-source:3.8`.

Compilation tests with capture checking are run with this option, as
well as `scala2-library-cc`.

Author: natsukagami

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

@@ -48,7 +48,7 @@ object ccConfig:
 
   /** If true, turn on separation checking */
   def useSepChecks(using Context): Boolean =
-    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
+    Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.8`)
 
   /** If true, do level checking for FreshCap instances */
   def useFreshLevels(using Context): Boolean =
@@ -58,4 +58,4 @@ object ccConfig:
   def newScheme(using Context): Boolean =
     Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
 
-end ccConfig
+end ccConfig

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")),
+      compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
       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")),
@@ -146,7 +146,7 @@ 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")),
+      compileFilesInDir("tests/neg-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking", "-source", "3.8")),
       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(
@@ -169,7 +169,7 @@ 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")),
+      compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking", "-source", "3.8")),
       // Run tests for legacy lazy vals.
       compileFilesInDir("tests/run", defaultOptions.and("-Wsafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
     ).checkRuns()

project/Build.scala

@@ -1236,7 +1236,10 @@ object Build {
     withCommonSettings(Bootstrapped).
     dependsOn(dottyCompiler(Bootstrapped) % "provided; compile->runtime; test->test").
     settings(scala2LibraryBootstrappedSettings).
-    settings(moduleName := "scala2-library-cc")
+    settings(
+      moduleName := "scala2-library-cc",
+      scalacOptions ++= Seq("-source", "3.8"), // for separation checking
+    )
 
   lazy val scala2LibraryBootstrappedSettings = Seq(
       javaOptions := (`scala3-compiler-bootstrapped` / javaOptions).value,