Imlement new import seclectors for givens

It's now
```scala
given _
given T
```
Thta way it's more regular: A given selector is always followed by something: Either
a wildcard or a type.

The previous syntax for type bounds on normal imports is no longer supported.
We might want to bring it back at some point, but it's not essential.

Author: odersky

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

@@ -2985,7 +2985,6 @@ object Parsers {
     /**  ImportExpr ::= StableId ‘.’ ImportSpec
      *   ImportSpec  ::=  id
      *                 | ‘_’
-     *                 | ‘given’
      *                 | ‘{’ ImportSelectors) ‘}’
      */
     def importExpr(mkTree: ImportConstr): () => Tree = {
@@ -3007,15 +3006,16 @@ object Parsers {
         val selector =
           if isWildcard then
             val id = wildcardSelectorId()
-            val bound =
-              if selToken == USCORE && in.token == COLON then
+            if selToken == USCORE then ImportSelector(id)
+            else atSpan(startOffset(id)) {
+              if in.token == USCORE then
                 in.nextToken()
-                infixType()
-              else if selToken == GIVEN && in.token != RBRACE && in.token != COMMA then
-                infixType()
+                ImportSelector(id)
+              else if in.token != RBRACE && in.token != COMMA then
+                ImportSelector(id, bound = infixType())
               else
-                EmptyTree
-            ImportSelector(id, bound = bound)
+                ImportSelector(id)  // TODO: drop
+            }
           else
             val from = termIdent()
             if !idOK then syntaxError(i"named imports cannot follow wildcard imports")

docs/docs/internals/syntax.md

@@ -342,12 +342,11 @@ Import            ::=  ‘import’ ImportExpr {‘,’ ImportExpr}
 ImportExpr        ::=  StableId ‘.’ ImportSpec                                  Import(expr, sels)
 ImportSpec        ::=  id
                     | ‘_’
-                    | ‘given’
                     | ‘{’ ImportSelectors) ‘}’
 ImportSelectors   ::=  id [‘=>’ id | ‘=>’ ‘_’] [‘,’ ImportSelectors]
                     |  WildCardSelector {‘,’ WildCardSelector}
-WildCardSelector  ::=  ‘given’ [InfixType]
-                    |  ‘_' [‘:’ InfixType]
+WildCardSelector  ::=  ‘given’ (‘_' | InfixType)
+                    |  ‘_'
 Export            ::=  ‘export’ [‘given’] ImportExpr {‘,’ ImportExpr}
 ```
 

tests/run/boundedImports.scala renamed to tests/invalid/run/boundedImports.scala

@@ -21,7 +21,7 @@ object D {
 }
 
 object Test {
-  import D.given
+  import D.{given _}
 
   val x1: A = new B
   val x2: B = new A  // error under -Xfatal-warnings -feature

tests/neg-custom-args/implicit-conversions.scala

@@ -4,7 +4,7 @@ import scala.quoted.matching._
 inline def f: Any = ${ fImpl }
 
 private def fImpl with (qctx: QuoteContext) : Expr[Unit] = {
-  import qctx.tasty.{_, given}
+  import qctx.tasty.{_, given _}
   searchImplicit(('[A]).unseal.tpe) match {
     case x: ImplicitSearchSuccess =>
       '{}

tests/neg-macros/delegate-match-1/Macro_1.scala

@@ -4,7 +4,7 @@ import scala.quoted.matching._
 inline def f: Any = ${ fImpl }
 
 private def fImpl with (qctx: QuoteContext) : Expr[Unit] = {
-  import qctx.tasty.{_, given}
+  import qctx.tasty.{_, given _}
   searchImplicit(('[A]).unseal.tpe) match {
     case x: ImplicitSearchSuccess =>
       '{}

tests/neg-macros/delegate-match-2/Macro_1.scala

@@ -4,7 +4,7 @@ import scala.quoted.matching._
 inline def f: Any = ${ fImpl }
 
 private def fImpl with (qctx: QuoteContext) : Expr[Unit] = {
-  import qctx.tasty.{_, given}
+  import qctx.tasty.{_, given _}
   searchImplicit(('[A]).unseal.tpe) match {
     case x: ImplicitSearchSuccess =>
       '{}

tests/neg-macros/delegate-match-3/Macro_1.scala

@@ -1,13 +1,13 @@
 
 import scala.quoted._
-import scala.quoted.autolift.given
+import scala.quoted.autolift.{given _}
 import scala.quoted.matching._
 
 object Macro {
   inline def (sc: => StringContext).foo(args: String*): Unit = ${ impl('sc) }
 
   def impl(sc: Expr[StringContext]) with (qctx: QuoteContext) : Expr[Unit] = {
-    import qctx.tasty.{_, given}
+    import qctx.tasty.{_, given _}
     sc match {
       case '{ StringContext(${ExprSeq(parts)}: _*) } =>
         for (part @ Const(s) <- parts)

tests/neg-macros/i6432/Macro_1.scala

@@ -1,13 +1,13 @@
 
 import scala.quoted._
-import scala.quoted.autolift.given
+import scala.quoted.autolift.{given _}
 import scala.quoted.matching._
 
 object Macro {
   inline def (sc: => StringContext).foo(args: String*): Unit = ${ impl('sc) }
 
   def impl(sc: Expr[StringContext]) with (qctx: QuoteContext) : Expr[Unit] = {
-    import qctx.tasty.{_, given}
+    import qctx.tasty.{_, given _}
     sc match {
       case '{ StringContext(${ExprSeq(parts)}: _*) } =>
         for (part @ Const(s) <- parts)

tests/neg-macros/i6432b/Macro_1.scala

@@ -1,14 +1,14 @@
 package playground
 
 import scala.quoted._, scala.quoted.matching._
-import scala.quoted.given
+import scala.quoted.{given _}
 import scala.tasty._
 
 object macros {
   inline def mcr(x: => Any) = ${mcrImpl('x)}
 
   def mcrImpl(body: Expr[Any]) with (ctx: QuoteContext) : Expr[Any] = {
-    import ctx.tasty.{_, given}
+    import ctx.tasty.{_, given _}
     body.unseal match { case Block(_, _) => '{2} }
   }
 }