Allow applications in export qualifiers

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3111,7 +3111,7 @@ object Parsers {
      */
     def importClause(leading: Token, mkTree: ImportConstr): List[Tree] = {
       val offset = accept(leading)
-      commaSeparated(importExpr(mkTree)) match {
+      commaSeparated(importExpr(mkTree, acceptArgs = leading == EXPORT)) match {
         case t :: rest =>
           // The first import should start at the start offset of the keyword.
           val firstPos =
@@ -3142,6 +3142,8 @@ object Parsers {
       imp
 
     /** ImportExpr       ::=  SimpleRef {‘.’ id} ‘.’ ImportSpec
+     *                     |  SimpleRef ‘as’ id
+     *  ExportExpr       ::=  SimpleRef {‘.’ id | ParArgumentExprs} ‘.’ ImportSpec
      *                     |  SimpleRef ‘as’ id
      *  ImportSpec       ::=  NamedSelector
      *                     |  WildcardSelector
@@ -3151,7 +3153,7 @@ object Parsers {
      *  NamedSelector    ::=  id [‘as’ (id | ‘_’)]
      *  WildCardSelector ::=  ‘*' | ‘given’ [InfixType]
      */
-    def importExpr(mkTree: ImportConstr): () => Tree =
+    def importExpr(mkTree: ImportConstr, acceptArgs: Boolean): () => Tree =
 
       /** ‘*' | ‘_' */
       def wildcardSelector() =
@@ -3216,6 +3218,8 @@ object Parsers {
               mkTree(qual1, namedSelector(from) :: Nil)
             case qual: Ident =>
               mkTree(EmptyTree, namedSelector(qual) :: Nil)
+        else if acceptArgs && in.token == LPAREN then
+          importSelection(atSpan(startOffset(qual)) { mkApply(qual, parArgumentExprs()) })
         else
           accept(DOT)
           in.token match

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

@@ -868,9 +868,15 @@ trait Checking {
         then
           report.error(em"no aliases can be used to refer to a language import", path.srcPos)
 
+  /** Check that `path` is a legal prefix for an export clause that exports a type */
+  def checkLegalExportPathForType(path: Tree, mbr: Symbol)(using Context): Unit =
+    checkLegalImportOrExportPath(path,
+      if !path.tpe.isStable // compute non-constant kind string only when we are sure that an error is issued
+      then i"export prefix for $mbr"
+      else "export prefix")
+
   /** Check that `path` is a legal prefix for an export clause */
   def checkLegalExportPath(path: Tree, selectors: List[untpd.ImportSelector])(using Context): Unit =
-    checkLegalImportOrExportPath(path, "export prefix")
     if
       selectors.exists(_.isWildcard)
       && path.tpe.classSymbol.is(PackageClass)

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

@@ -1150,7 +1150,11 @@ class Namer { typer: Typer =>
                 case tp: TermRef => tp.termSymbol.is(Private) || refersToPrivate(tp.prefix)
                 case _ => false
               val (maybeStable, mbrInfo) =
-                if sym.isStableMember && sym.isPublic && !refersToPrivate(path.tpe) then
+                if sym.isStableMember
+                    && sym.isPublic
+                    && path.tpe.isStable
+                    && !refersToPrivate(path.tpe)
+                then
                   (StableRealizable, ExprType(path.tpe.select(sym)))
                 else
                   (EmptyFlags, mbr.info.ensureMethodic)
@@ -1165,6 +1169,7 @@ class Namer { typer: Typer =>
           forwarder.addAnnotations(sym.annotations.filterConserve(_.symbol != defn.BodyAnnot))
 
           if forwarder.isType then
+            checkLegalExportPathForType(path, sym)
             buf += tpd.TypeDef(forwarder.asType).withSpan(span)
           else
             import tpd._

docs/_docs/internals/syntax.md

@@ -259,7 +259,7 @@ SimpleExpr        ::=  SimpleRef
                     |  SimpleExpr ‘_’                                           PostfixOp(expr, _) (to be dropped)
                     |  XmlExpr													                        -- to be dropped
 IndentedExpr      ::=  indent CaseClauses | Block outdent
-Quoted            ::=  ‘'’ ‘{’ Block ‘}’  
+Quoted            ::=  ‘'’ ‘{’ Block ‘}’
                     |  ‘'’ ‘[’ Type ‘]’
 ExprsInParens     ::=  ExprInParens {‘,’ ExprInParens}
 ExprInParens      ::=  PostfixExpr ‘:’ Type                                     -- normal Expr allows only RefinedType here
@@ -366,9 +366,11 @@ AccessQualifier   ::=  ‘[’ id ‘]’
 Annotation        ::=  ‘@’ SimpleType1 {ParArgumentExprs}                         Apply(tpe, args)
 
 Import            ::=  ‘import’ ImportExpr {‘,’ ImportExpr}
-Export            ::=  ‘export’ ImportExpr {‘,’ ImportExpr}
 ImportExpr        ::=  SimpleRef {‘.’ id} ‘.’ ImportSpec                          Import(expr, sels)
                     |  SimpleRef ‘as’ id                                          Import(EmptyTree, ImportSelector(ref, id))
+Export            ::=  ‘export’ ExportExpr {‘,’ ExportExpr}
+ExportExpr        ::=  SimpleRef {‘.’ id | ParArgumentExprs} ‘.’ ImportSpec       Export(expr, sels)
+                    |  SimpleRef ‘as’ id                                          Export(EmptyTree, ImportSelector(ref, id))
 ImportSpec        ::=  NamedSelector
                     |  WildcardSelector
                     | ‘{’ ImportSelectors) ‘}’

docs/_docs/reference/other-new-features/export.md

@@ -44,22 +44,22 @@ val copier = new Copier
 copier.print(copier.scan())
 ```
 
-An `export` clause has the same format as an import clause. Its general form is:
+An `export` clause has a similar format as an import clause. Its general form is:
 
 ```scala
-export path . { sel_1, ..., sel_n }
+export qual . { sel_1, ..., sel_n }
 ```
 
-It consists of a qualifier expression `path`, which must be a stable identifier, followed by
+It consists of a qualifier expression `qual` followed by
 one or more selectors `sel_i` that identify what gets an alias. Selectors can be
 of one of the following forms:
 
- - A _simple selector_ `x` creates aliases for all eligible members of `path` that are named `x`.
- - A _renaming selector_ `x => y` creates aliases for all eligible members of `path` that are named `x`, but the alias is named `y` instead of `x`.
+ - A _simple selector_ `x` creates aliases for all eligible members of `qual` that are named `x`.
+ - A _renaming selector_ `x => y` creates aliases for all eligible members of `qual` that are named `x`, but the alias is named `y` instead of `x`.
  - An _omitting selector_ `x => _` prevents `x` from being aliased by a subsequent
    wildcard selector.
  - A _given selector_ `given x` has an optional type bound `x`. It creates aliases for all eligible given instances that conform to either `x`, or `Any` if `x` is omitted, except for members that are named by a previous simple, renaming, or omitting selector.
- - A _wildcard selector_ `*` creates aliases for all eligible members of `path` except for given instances,
+ - A _wildcard selector_ `*` creates aliases for all eligible members of `qual` except for given instances,
    synthetic members generated by the compiler and those members that are named by a previous simple, renaming, or omitting selector.
    \
    Notes:
@@ -77,6 +77,18 @@ A member is _eligible_ if all of the following holds:
 
 It is a compile-time error if a simple or renaming selector does not identify any eligible members.
 
+The qualifier expression `qual` can contain selections as well as applications
+to arguments. However, if a type member is exported, `qual` must be a stable path.
+
+Example:
+
+```scala
+class C(x: Int) { type T; def m = x }
+export C(2).m  // OK, generates:   def m = C(2).m
+export C(3).T  // error: need a path to export T
+export C(4).*  // also error since T is exported via *
+```
+
 Type members are aliased by type definitions, and term members are aliased by method definitions. Export aliases copy the type and value parameters of the members they refer to.
 Export aliases are always `final`. Aliases of given instances are again defined as givens (and aliases of old-style implicits are `implicit`). Aliases of extensions are again defined as extensions. Aliases of inline methods or values are again defined `inline`. There are no other modifiers that can be given to an alias. This has the following consequences for overriding:
 
@@ -85,8 +97,7 @@ Export aliases are always `final`. Aliases of given instances are again defined
    not marked `override`.
  - However, export aliases can implement deferred members of base classes.
 
-Export aliases for public value definitions that are accessed without
-referring to private values in the qualifier path
+If the qualifier is a stable path, export aliases for public value definitions that are accessed without referring to private values in that path
 are marked by the compiler as "stable" and their result types are the singleton types of the aliased definitions. This means that they can be used as parts of stable identifier paths, even though they are technically methods. For instance, the following is OK:
 ```scala
 class C { type T }
@@ -99,7 +110,7 @@ def f: c.T = ...
 **Restrictions:**
 
  1. Export clauses can appear in classes or they can appear at the top-level. An   export clause cannot appear as a statement in a block.
- 1. If an export clause contains a wildcard or given selector, it is forbidden for its qualifier path to refer to a package. This is because it is not yet known how to safely track wildcard dependencies to a package for the purposes of incremental compilation.
+ 1. If an export clause contains a wildcard or given selector, it is forbidden for its qualifier to refer to a package. This is because it is not yet known how to safely track wildcard dependencies to a package for the purposes of incremental compilation.
 
  1. Simple renaming exports like
     ```scala
@@ -130,8 +141,9 @@ TemplateStat      ::=  ...
                     |  Export
 TopStat           ::=  ...
                     |  Export
-Export            ::=  ‘export’ ImportExpr {‘,’ ImportExpr}
-ImportExpr        ::=  SimpleRef {‘.’ id} ‘.’ ImportSpec
+Export            ::=  ‘export’ ExportExpr {‘,’ ExportExpr}
+ExportExpr        ::=  SimpleRef {‘.’ id | ParArgumentExprs} ‘.’ ImportSpec
+                    |  SimpleRef ‘as’ id
 ImportSpec        ::=  NamedSelector
                     |  WildcardSelector
                     | ‘{’ ImportSelectors) ‘}’
@@ -173,9 +185,8 @@ Export clauses are processed when the type information of the enclosing object o
 
     With export clauses, the following steps are added:
 
- 6. Compute the types of all paths in export clauses.
- 7. Enter export aliases for the eligible members of all paths in export clauses.
+ 6. Compute the types of all qualifiers in export clauses.
+ 7. Enter export aliases for the eligible members of all qualifiers in export clauses.
 
 It is important that steps 6 and 7 are done in sequence: We first compute the types of _all_
-paths in export clauses and only after this is done we enter any export aliases as class members. This means that a path of an export clause cannot refer to an alias made available
-by another export clause of the same class.
+qualifiers in export clauses and only after this is done we enter any export aliases as class members. This means that a qualifier of an export clause cannot refer to an alias made available by another export clause of the same class.

docs/_docs/reference/syntax.md

@@ -355,9 +355,11 @@ AccessQualifier   ::=  ‘[’ id ‘]’
 Annotation        ::=  ‘@’ SimpleType1 {ParArgumentExprs}
 
 Import            ::=  ‘import’ ImportExpr {‘,’ ImportExpr}
-Export            ::=  ‘export’ ImportExpr {‘,’ ImportExpr}
 ImportExpr        ::=  SimpleRef {‘.’ id} ‘.’ ImportSpec
                     |  SimpleRef ‘as’ id
+Export            ::=  ‘export’ ExportExpr {‘,’ ExportExpr}
+ExportExpr        ::=  SimpleRef {‘.’ id | ParArgumentExprs} ‘.’ ImportSpec
+                    |  SimpleRef ‘as’ id
 ImportSpec        ::=  NamedSelector
                     |  WildcardSelector
                     | ‘{’ ImportSelectors) ‘}’

tests/neg/exports.check

@@ -58,3 +58,9 @@
    |               Double definition:
    |               val bar: Bar in class Baz at line 45 and
    |               final def bar: (Baz.this.bar.bar : => (Baz.this.bar.baz.bar : Bar)) in class Baz at line 46
+-- [E083] Type Error: tests/neg/exports.scala:57:11 --------------------------------------------------------------------
+57 |    export printer("#1").*  // error
+   |           ^^^^^^^^^^^^^
+   |           Printer is not a valid export prefix for type PrinterType, since it is not an immutable path
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/exports.scala

@@ -49,3 +49,9 @@
     val baz: Baz = new Baz
     export baz._
   }
+
+  object No:
+    def printer(id: String) =
+      println(s"new Printer $id")
+      new Printer
+    export printer("#1").*  // error

tests/run/exports.check

@@ -5,3 +5,8 @@ config
 printing
 scanning
 scanning
+new Printer #1
+printing
+new Printer #1
+printing
+scanning

tests/run/exports.scala

@@ -18,8 +18,8 @@ object Test extends App {
 
   object Copier {
     val printer = new Printer
-    export printer.{given, _}
-    export Scanner.{scan => scanIt, _}
+    export printer.{given, *}
+    export Scanner.{scan => scanIt, *}
 
     val config2 = summon[Config]
   }
@@ -41,6 +41,17 @@ object Test extends App {
   test()
 
   val _: Int = B.x
+
+  object FunnyCopier:
+    def printer(id: String) =
+      println(s"new Printer $id")
+      new Printer
+    export printer("#1").*
+    export Scanner.*
+
+  FunnyCopier.print()
+  FunnyCopier.print()
+  FunnyCopier.scan()
 }
 
 final class Foo {