Root of Java select must be class or rooted package (#21800)

Fixes #21333 

Edge case in Java interop.

compiler/src/dotty/tools/dotc/reporting/MessageRendering.scala

@@ -62,7 +62,7 @@ trait MessageRendering {
     }
 
     val syntax =
-      if (ctx.settings.color.value != "never")
+      if (ctx.settings.color.value != "never" && !ctx.isJava)
         SyntaxHighlighting.highlight(new String(pos.linesSlice)).toCharArray
       else pos.linesSlice
     val lines = linesFrom(syntax)

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

@@ -125,8 +125,8 @@ trait TypeAssigner {
 
   /** The type of the selection `tree`, where `qual1` is the typed qualifier part. */
   def selectionType(tree: untpd.RefTree, qual1: Tree)(using Context): Type =
-    val qualType0 = qual1.tpe.widenIfUnstable
     val qualType =
+      val qualType0 = qual1.tpe.widenIfUnstable
       if !qualType0.hasSimpleKind && tree.name != nme.CONSTRUCTOR then
         // constructors are selected on type constructor, type arguments are passed afterwards
         errorType(em"$qualType0 takes type parameters", qual1.srcPos)
@@ -199,7 +199,7 @@ trait TypeAssigner {
 
   /** Type assignment method. Each method takes as parameters
    *   - an untpd.Tree to which it assigns a type,
-   *   - typed child trees it needs to access to cpmpute that type,
+   *   - typed child trees it needs to access to compute that type,
    *   - any further information it needs to access to compute that type.
    */
   def assignType(tree: untpd.Ident, tp: Type)(using Context): Ident =

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

@@ -1022,20 +1022,44 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     record("typedSelect")
 
     def typeSelectOnTerm(using Context): Tree =
-      val qual = typedExpr(tree.qualifier, shallowSelectionProto(tree.name, pt, this, tree.nameSpan))
       if ctx.isJava then
-        javaSelection(qual)
+        // permitted selection depends on Java context (type or expression).
+        // we don't propagate (as a mode) whether a.b.m is a type name; OK since we only see type contexts.
+        // to allow correct selections, approximate by fallback for x.y: take x as class or (rooted) package.
+        def tryQualFallback(qual: untpd.Ident, name: Name)(using Context): Tree =
+          val qualTpe =
+            findRef(name.toTypeName, WildcardType, EmptyFlags, EmptyFlags, qual.srcPos) match
+            case tpe: NamedType if tpe.symbol.isClass => tpe
+            case _ =>
+              val maybePackage = defn.RootPackage.info.member(name)
+              if maybePackage.exists then maybePackage.info else NoType
+          if qualTpe.exists then
+            javaSelection(assignType(cpy.Ident(qual)(name), qualTpe))
+          else
+            errorTree(tree, em"no class or package to resolve `$name`") // just fail fallback
+        def tryQual(qual: untpd.Tree)(using Context): Tree =
+          javaSelection(typedExpr(qual, shallowSelectionProto(tree.name, pt, this, tree.nameSpan)))
+        tree.qualifier match
+        case qual @ Ident(name) => tryAlternatively(tryQual(qual))(tryQualFallback(qual, name))
+        case qual               => tryQual(qual)
       else
+        val qual = typedExpr(tree.qualifier, shallowSelectionProto(tree.name, pt, this, tree.nameSpan))
         typedSelectWithAdapt(tree, pt, qual).withSpan(tree.span).computeNullable()
 
     def javaSelection(qual: Tree)(using Context) =
-      val tree1 = assignType(cpy.Select(tree)(qual, tree.name), qual)
-      tree1.tpe match
-        case moduleRef: TypeRef if moduleRef.symbol.is(ModuleClass, butNot = JavaDefined) =>
-          // handle unmangling of module names (Foo$ -> Foo[ModuleClass])
-          cpy.Select(tree)(qual, tree.name.unmangleClassName).withType(moduleRef)
-        case _ =>
-          tree1
+      qual match
+      case id @ Ident(name) if id.symbol.is(Package) && !id.symbol.owner.isRoot =>
+        val rooted = defn.RootPackage.info.member(name)
+        val qual1 = if rooted.exists then assignType(cpy.Ident(id)(name), rooted.info) else qual
+        assignType(cpy.Select(tree)(qual1, tree.name), qual1)
+      case _ =>
+        val tree1 = assignType(cpy.Select(tree)(qual, tree.name), qual)
+        tree1.tpe match
+          case moduleRef: TypeRef if moduleRef.symbol.is(ModuleClass, butNot = JavaDefined) =>
+            // handle unmangling of module names (Foo$ -> Foo[ModuleClass])
+            cpy.Select(tree)(qual, tree.name.unmangleClassName).withType(moduleRef)
+          case _ =>
+            tree1
 
     def tryJavaSelectOnType(using Context): Tree = tree.qualifier match {
       case sel @ Select(qual, name) =>
@@ -1052,17 +1076,14 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         errorTree(tree, em"cannot convert to type selection") // will never be printed due to fallback
     }
 
-    def selectWithFallback(fallBack: Context ?=> Tree) =
-      tryAlternatively(typeSelectOnTerm)(fallBack)
-
     if (tree.qualifier.isType) {
       val qual1 = typedType(tree.qualifier, shallowSelectionProto(tree.name, pt, this, tree.nameSpan))
       assignType(cpy.Select(tree)(qual1, tree.name), qual1)
     }
     else if (ctx.isJava && tree.name.isTypeName)
-      // SI-3120 Java uses the same syntax, A.B, to express selection from the
-      // value A and from the type A. We have to try both.
-      selectWithFallback(tryJavaSelectOnType) // !!! possibly exponential bcs of qualifier retyping
+      // scala/bug#3120 Java uses the same syntax, A.B, to express selection from the
+      // value A and from the type A. We have to try both. (possibly exponential bc of qualifier retyping)
+      tryAlternatively(typeSelectOnTerm)(tryJavaSelectOnType)
     else
       typeSelectOnTerm
   }

tests/pos/t10350/Bar.scala

@@ -0,0 +1,6 @@
+
+package bar
+
+object Bar {
+  def xxx(s: String): foo.Foo = foo.Foo.create(s)
+}

tests/pos/t10350/Baz.java

@@ -0,0 +1,5 @@
+
+package foo.java;
+
+interface Baz {
+}

tests/pos/t10350/Foo.java

@@ -0,0 +1,14 @@
+
+package foo;
+
+public interface Foo {
+  static Foo create(java.lang.String v) {
+    return null;
+  }
+}
+
+/*
+5 |  static Foo create(java.lang.String v) {
+  |                    ^^^^^^^^^
+  |                    value lang is not a member of foo.java
+ */

tests/pos/t11788/Bar.scala

@@ -0,0 +1,5 @@
+package p
+
+object Bar extends App {
+  println(new Foo().test())
+}

tests/pos/t11788/Foo.java

@@ -0,0 +1,11 @@
+package p;
+
+public class Foo {
+	private String java;
+
+	// java is the rooted package, not the field
+	public java.lang.Integer test() {
+		//return Integer.valueOf(42);
+		throw null;
+	}
+}

tests/pos/t11788b/Bar.scala

@@ -0,0 +1,5 @@
+package p
+
+object Bar extends App {
+  println(new Foo().test())
+}

tests/pos/t11788b/Foo.java

@@ -0,0 +1,10 @@
+package p;
+
+public class Foo {
+	private String java;
+
+	public java.lang.Integer test() {
+		//return Integer.valueOf(42);
+		throw null;
+	}
+}

tests/pos/t11788b/java.java

@@ -0,0 +1,8 @@
+package p;
+
+public class java {
+	public static class lang {
+		public static class Integer {
+		}
+	}
+}

tests/pos/t11788c/Bar.scala

@@ -0,0 +1,5 @@
+package p
+
+object Bar extends App {
+  println(new Foo().test())
+}

tests/pos/t11788c/Foo.java

@@ -0,0 +1,10 @@
+package p;
+
+public class Foo {
+	private String java;
+
+	// java is class in scope, not the term member or package
+	public java.lang.Integer.Inner test() {
+		throw null;
+	}
+}

tests/pos/t11788c/java.java

@@ -0,0 +1,10 @@
+package p;
+
+public class java {
+	public static class lang {
+		public static class Integer {
+			public static class Inner {
+			}
+		}
+	}
+}