Check import selectors at Typer

Import selectors were checked  at PostTyper before, but that can lead
to confusion when a type error results from a bad import selector.

Fixes #15468

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeErrors.scala

@@ -41,7 +41,8 @@ class MissingType(pre: Type, name: Name) extends TypeError {
   }
 }
 
-class RecursionOverflow(val op: String, details: => String, val previous: Throwable, val weight: Int) extends TypeError {
+class RecursionOverflow(val op: String, details: => String, val previous: Throwable, val weight: Int)
+extends TypeError {
 
   def explanation: String = s"$op $details"
 

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -430,21 +430,6 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
               case tpe => tpe
             }
           )
-        case Import(expr, selectors) =>
-          val exprTpe = expr.tpe
-          val seen = mutable.Set.empty[Name]
-
-          def checkIdent(sel: untpd.ImportSelector): Unit =
-            if !exprTpe.member(sel.name).exists
-               && !exprTpe.member(sel.name.toTypeName).exists then
-              report.error(NotAMember(exprTpe, sel.name, "value"), sel.imported.srcPos)
-            if seen.contains(sel.name) then
-              report.error(ImportRenamedTwice(sel.imported), sel.imported.srcPos)
-            seen += sel.name
-
-          for sel <- selectors do
-            if !sel.isWildcard then checkIdent(sel)
-          super.transform(tree)
         case Typed(Ident(nme.WILDCARD), _) =>
           withMode(Mode.Pattern)(super.transform(tree))
             // The added mode signals that bounds in a pattern need not

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

@@ -1429,6 +1429,27 @@ trait Checking {
         em"""Implementation restriction: cannot generate CanThrow capability for this kind of catch.
             |CanThrow capabilities can only be generated $req.""",
         pat.srcPos)
+
+  /** (1) Check that every named import selector refers to a type or value member of the
+   *  qualifier type.
+   *  (2) Check that no import selector is renamed more than once.
+   */
+  def checkImportSelectors(qualType: Type, selectors: List[untpd.ImportSelector])(using Context): Unit =
+    val seen = mutable.Set.empty[Name]
+
+    def checkIdent(sel: untpd.ImportSelector): Unit =
+      if sel.name != nme.ERROR
+          && !qualType.member(sel.name).exists
+          && !qualType.member(sel.name.toTypeName).exists
+      then
+        report.error(NotAMember(qualType, sel.name, "value"), sel.imported.srcPos)
+      if seen.contains(sel.name) then
+        report.error(ImportRenamedTwice(sel.imported), sel.imported.srcPos)
+      seen += sel.name
+
+    for sel <- selectors do
+      if !sel.isWildcard then checkIdent(sel)
+  end checkImportSelectors
 }
 
 trait ReChecking extends Checking {
@@ -1466,4 +1487,5 @@ trait NoChecking extends ReChecking {
   override def checkMembersOK(tp: Type, pos: SrcPos)(using Context): Type = tp
   override def checkInInlineContext(what: String, pos: SrcPos)(using Context): Unit = ()
   override def checkValidInfix(tree: untpd.InfixOp, meth: Symbol)(using Context): Unit = ()
+  override def checkImportSelectors(qualType: Type, selectors: List[untpd.ImportSelector])(using Context): Unit = ()
 }

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

@@ -2606,6 +2606,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val expr1 = typedImportQualifier(imp, typedExpr(_, _)(using ctx.withOwner(sym)))
     checkLegalImportPath(expr1)
     val selectors1 = typedSelectors(imp.selectors)
+    checkImportSelectors(expr1.tpe, selectors1)
     assignType(cpy.Import(imp)(expr1, selectors1), sym)
 
   def typedExport(exp: untpd.Export)(using Context): Tree =

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

@@ -1,3 +1,7 @@
+-- [E008] Not Found Error: tests/neg-custom-args/jdk-9-app.scala:1:17 --------------------------------------------------
+1 |import java.lang.ProcessHandle // error: not a member
+  |                 ^^^^^^^^^^^^^
+  |                 value ProcessHandle is not a member of java.lang
 -- [E006] Not Found Error: tests/neg-custom-args/jdk-9-app.scala:4:10 --------------------------------------------------
 4 |  println(ProcessHandle.current().pid()) // error: not found
   |          ^^^^^^^^^^^^^

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

@@ -1,4 +1,4 @@
-import java.lang.ProcessHandle
+import java.lang.ProcessHandle // error: not a member
 
 object Jdk9App extends App {
   println(ProcessHandle.current().pid()) // error: not found

tests/neg/deriving.scala

@@ -1,4 +1,4 @@
-import reflect.Generic
+import reflect.Generic // error: Generic is not a member of reflect
 
 sealed trait A derives Generic // error: cannot take shape, it has anonymous or inaccessible subclasses
 

tests/neg/i15468.scala

@@ -0,0 +1,6 @@
+object Test {
+  val s = ""
+  import s.{length => x, size => y} // error: size is not a member of s
+  locally(x) // ok
+  locally(size) // error: Not found: y
+}

tests/neg/i6056.scala

@@ -1,5 +1,5 @@
 object i0{
-    import i0.i0   // error
+    import i0.i0   // error // error
     def i0={
         import _  // error
         import    // error

tests/neg/implicitDefs.scala

@@ -1,6 +1,6 @@
 package test
 
-import Predef.{any2stringadd as _, StringAdd as _, *}
+import Predef.{any2stringadd as _, *}
 
 object implicitDefs {
 

tests/neg/language-import.scala

@@ -3,7 +3,7 @@ object a:
   import l.noAutoTupling     // error
   import l.experimental.genericNumberLiterals  // error
   val scala = c
-  import scala.language.noAutoTupling  // error
+  import scala.language.noAutoTupling  // error // error
   val language = b
   import language.experimental.genericNumberLiterals // error
 

tests/neg/parser-stability-23.scala

@@ -1,3 +1,3 @@
 object i0 {
-  import Ordering.{ implicitly as } (true: Boolean) match { case _: i1 as true } // error // error
+  import Ordering.{ implicitly as } (true: Boolean) match { case _: i1 as true } // error // error // error
 }

tests/neg/rootImplicits.scala

@@ -1,6 +1,6 @@
 package test
 
-import Predef.{any2stringadd as _, StringAdd as _, *}
+import Predef.{any2stringadd as _, *}
 
 object rootImplicits {