Consider minTargetVersion as always supported

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

@@ -24,7 +24,7 @@ object ScalaSettings:
       val jdkVersion = JDK9Reflectors.runtimeVersionMajor(JDK9Reflectors.runtimeVersion()).intValue()
       val maxVersion = Math.min(jdkVersion, maxTargetVersion)
       (minTargetVersion to maxVersion).toList.map(_.toString)
-    else List()
+    else List(minTargetVersion).map(_.toString)
 
   def defaultClasspath: String = sys.env.getOrElse("CLASSPATH", ".")
 

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

@@ -64,6 +64,7 @@ class CompilationTests {
       compileFile("tests/pos-custom-args/help.scala", defaultOptions.and("-help", "-V", "-W", "-X", "-Y")),
       compileFile("tests/pos-custom-args/i10383.scala", defaultOptions.and("-source", "future", "-deprecation", "-Xfatal-warnings")),
       compileFile("tests/pos-custom-args/i13044.scala", defaultOptions.and("-Xmax-inlines:33")),
+      compileFile("tests/pos-custom-args/jdk-8-app.scala", defaultOptions.and("-release:8")),
     ).checkCompile()
   }
 
@@ -184,6 +185,7 @@ class CompilationTests {
       compileDir("tests/neg-custom-args/hidden-type-errors", defaultOptions.and("-explain")),
       compileFile("tests/neg-custom-args/i13026.scala", defaultOptions.and("-print-lines")),
       compileFile("tests/neg-custom-args/i13838.scala", defaultOptions.and("-Ximplicit-search-limit", "1000")),
+      compileFile("tests/neg-custom-args/jdk-9-app.scala", defaultOptions.and("-release:8")),
     ).checkExpectedErrors()
   }
 

tests/neg-custom-args/jdk-9-app.check

@@ -0,0 +1,6 @@
+-- [E006] Not Found Error: tests/neg-custom-args/jdk-9-app.scala:4:10 --------------------------------------------------
+4 |  println(ProcessHandle.current().pid()) // error: not found
+  |          ^^^^^^^^^^^^^
+  |          Not found: ProcessHandle
+
+longer explanation available when compiling with `-explain`

tests/neg-custom-args/jdk-9-app.scala

@@ -0,0 +1,5 @@
+import java.lang.ProcessHandle
+
+object Jdk9App extends App {
+  println(ProcessHandle.current().pid()) // error: not found
+}

tests/pos-custom-args/jdk-8-app.scala

@@ -0,0 +1,5 @@
+import java.time.LocalDate
+
+object Jdk8App extends App {
+  println(LocalDate.now())
+}