Avoid most deep subtypes in test

The only remaining testcase requiring deep subtype is t8146a.scala for
good reasons.

Author: smarter

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1089,8 +1089,20 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
         isApplicable(alt2, formals1, WildcardType) ||
         tp1.paramInfos.isEmpty && tp2.isInstanceOf[LambdaType]
       case tp1: PolyType => // (2)
-        val tparams = ctx.newTypeParams(alt1.symbol, tp1.paramNames, EmptyFlags, tp1.instantiateBounds)
-        isAsSpecific(alt1, tp1.instantiate(tparams.map(_.typeRef)), alt2, tp2)
+        val nestedCtx = ctx.fresh.setExploreTyperState()
+
+        {
+          implicit val ctx = nestedCtx
+
+          // Fully define the type so that the types of the tparams created
+          // below never contain TypeRefs whose underling types contain
+          // uninstantiated TypeVars, this could lead to cycles in `isSubType`
+          // as a TypeVar might get constrained by a TypeRef it's part of.
+          val tp1a = fullyDefinedType(tp1, "alternative", alt1.symbol.pos).asInstanceOf[PolyType]
+
+          val tparams = ctx.newTypeParams(alt1.symbol, tp1.paramNames, EmptyFlags, tp1a.instantiateBounds)
+          isAsSpecific(alt1, tp1a.instantiate(tparams.map(_.typeRef)), alt2, tp2)
+        }
       case _ => // (3)
         tp2 match {
           case tp2: MethodType => true // (3a)

compiler/test/dotc/tests.scala

@@ -168,7 +168,6 @@ class tests extends CompilerTest {
 
   @Test def rewrites = compileFile(posScala2Dir, "rewrites", "-rewrite" :: scala2mode)
 
-  @Test def pos_t8146a = compileFile(posSpecialDir, "t8146a")(allowDeepSubtypes)
   @Test def pos_jon = compileFile(posSpecialDir, "jon")(allowDeepSubtypes)
 
   @Test def pos_t5545 = {

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

@@ -40,8 +40,8 @@ class CompilationTests extends ParallelTesting {
     compileList("compileStdLib", StdLibSources.whitelisted, scala2Mode.and("-migration", "-Yno-inline")) +
     compileDir("../compiler/src/dotty/tools/dotc/ast", defaultOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/config", defaultOptions) +
-    compileDir("../compiler/src/dotty/tools/dotc/core", allowDeepSubtypes) +
-    compileDir("../compiler/src/dotty/tools/dotc/transform", allowDeepSubtypes) +
+    compileDir("../compiler/src/dotty/tools/dotc/core", defaultOptions) +
+    compileDir("../compiler/src/dotty/tools/dotc/transform", defaultOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/parsing", defaultOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/printing", defaultOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/reporting", defaultOptions) +
@@ -51,7 +51,6 @@ class CompilationTests extends ParallelTesting {
     compileDir("../compiler/src/dotty/tools/dotc/core", TestFlags(classPath, noCheckOptions)) +
     compileFile("../tests/pos/nullarify.scala", defaultOptions.and("-Ycheck:nullarify")) +
     compileFile("../tests/pos-scala2/rewrites.scala", scala2Mode.and("-rewrite")).copyToTarget() +
-    compileFile("../tests/pos-special/t8146a.scala", allowDeepSubtypes) +
     compileFile("../tests/pos-special/utf8encoded.scala", explicitUTF8) +
     compileFile("../tests/pos-special/utf16encoded.scala", explicitUTF16) +
     compileList(
@@ -198,8 +197,8 @@ class CompilationTests extends ParallelTesting {
   // lower level of concurrency as to not kill their running VMs
 
   @Test def testPickling: Unit = {
-    compileDir("../compiler/src/dotty/tools", picklingOptionsAllowDeepSubTypes) +
-    compileDir("../compiler/src/dotty/tools/dotc", picklingOptionsAllowDeepSubTypes) +
+    compileDir("../compiler/src/dotty/tools", picklingOptions) +
+    compileDir("../compiler/src/dotty/tools/dotc", picklingOptions) +
     compileFilesInDir("../tests/new", picklingOptions) +
     compileFilesInDir("../tests/pickling", picklingOptions) +
     compileDir("../library/src/dotty/runtime", picklingOptions) +
@@ -211,7 +210,7 @@ class CompilationTests extends ParallelTesting {
     compileDir("../compiler/src/dotty/tools/dotc/printing", picklingOptions) +
     compileDir("../compiler/src/dotty/tools/repl", picklingOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/rewrite", picklingOptions) +
-    compileDir("../compiler/src/dotty/tools/dotc/transform", picklingOptionsAllowDeepSubTypes) +
+    compileDir("../compiler/src/dotty/tools/dotc/transform", picklingOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/typer", picklingOptions) +
     compileDir("../compiler/src/dotty/tools/dotc/util", picklingOptions) +
     compileDir("../compiler/src/dotty/tools/io", picklingOptions) +
@@ -237,7 +236,7 @@ class CompilationTests extends ParallelTesting {
 
     def lib =
       compileDir("../library/src",
-        allowDeepSubtypes.and("-Ycheck-reentrant", "-strict", "-priorityclasspath", defaultOutputDir))
+        defaultOptions.and("-Ycheck-reentrant", "-strict", "-priorityclasspath", defaultOutputDir))
 
     val compilerDir = Paths.get("../compiler/src")
     val compilerSources = sources(Files.walk(compilerDir))

compiler/test/dotty/tools/vulpix/TestConfiguration.scala

@@ -55,7 +55,6 @@ object TestConfiguration {
     "-Ytest-pickler",
     "-Yprintpos"
   )
-  val picklingOptionsAllowDeepSubTypes = picklingOptions without "-Yno-deep-subtypes"
   val scala2Mode = defaultOptions and "-language:Scala2"
   val explicitUTF8 = defaultOptions and ("-encoding", "UTF8")
   val explicitUTF16 = defaultOptions and ("-encoding", "UTF16")