Make code completions and import suggestions work correctly for extensions with leading using clauses

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -13,12 +13,12 @@ import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.core.Names.{Name, TermName}
 import dotty.tools.dotc.core.NameKinds.SimpleNameKind
 import dotty.tools.dotc.core.NameOps._
-import dotty.tools.dotc.core.Symbols.{NoSymbol, Symbol, defn, newSymbol}
+import dotty.tools.dotc.core.Symbols.{NoSymbol, Symbol, TermSymbol, defn, newSymbol}
 import dotty.tools.dotc.core.Scopes
 import dotty.tools.dotc.core.StdNames.{nme, tpnme}
 import dotty.tools.dotc.core.TypeComparer
 import dotty.tools.dotc.core.TypeError
-import dotty.tools.dotc.core.Types.{ExprType, MethodType, NameFilter, NamedType, NoType, PolyType, Type}
+import dotty.tools.dotc.core.Types.{ExprType, MethodOrPoly, NameFilter, NamedType, NoType, PolyType, Type}
 import dotty.tools.dotc.printing.Texts._
 import dotty.tools.dotc.util.{NameTransformer, NoSourcePosition, SourcePosition}
 
@@ -216,28 +216,25 @@ object Completion {
       }
 
     def addExtensionCompletions(path: List[Tree], qual: Tree)(using Context): Unit =
-      def applyExtensionReceiver(methodSymbol: Symbol, methodName: TermName): Symbol = {
-        val newMethodType = methodSymbol.info match {
-          case mt: MethodType =>
-            mt.resultType match {
-              case resType: MethodType => resType
-              case resType => ExprType(resType)
-            }
-          case pt: PolyType =>
-            PolyType(pt.paramNames)(_ => pt.paramInfos, _ => pt.resultType.resultType)
-        }
-
-        newSymbol(owner = qual.symbol, methodName, methodSymbol.flags, newMethodType)
-      }
+      def asDefLikeType(tpe: Type): Type = tpe match
+        case _: MethodOrPoly => tpe
+        case _ => ExprType(tpe)
+
+      def tryApplyingReceiver(methodSym: TermSymbol): Option[TermSymbol] =
+        ctx.typer.tryApplyingReceiver(methodSym, qual)
+          .map { tree =>
+            val tpe = asDefLikeType(tree.tpe.dealias)
+            newSymbol(owner = qual.symbol, methodSym.name, methodSym.flags, tpe)
+          }
 
       val matchingNamePrefix = completionPrefix(path, pos)
 
       def extractDefinedExtensionMethods(types: Seq[Type]) =
         types
           .flatMap(_.membersBasedOnFlags(required = ExtensionMethod, excluded = EmptyFlags))
           .collect{ denot =>
-            denot.name.toTermName match {
-              case name if name.startsWith(matchingNamePrefix) => (denot.symbol, name)
+            denot.name match {
+              case name: TermName if name.startsWith(matchingNamePrefix) => (denot.symbol.asTerm, name)
             }
           }
 
@@ -248,7 +245,7 @@ object Completion {
         val buf = completionBuffer(path, pos)
         buf.addScopeCompletions
         buf.completions.mappings.toList.flatMap {
-          case (termName, symbols) => symbols.map(s => (s, termName))
+          case (termName, symbols) => symbols.map(s => (s.asTerm, termName))
         }
 
       // 2. The extension method is a member of some given instance that is visible at the point of the reference.
@@ -264,9 +261,12 @@ object Completion {
       val extMethodsFromGivensInImplicitScope = extractDefinedExtensionMethods(givensInImplicitScope)
 
       val availableExtMethods = extMethodsFromGivensInImplicitScope ++ extMethodsFromImplicitScope ++ extMethodsFromGivensInScope ++ extMethodsInScope
-      val extMethodsWithAppliedReceiver = availableExtMethods.collect {
-        case (symbol, termName) if ctx.typer.isApplicableExtensionMethod(symbol.termRef, qual.tpe) =>
-          applyExtensionReceiver(symbol, termName)
+
+      val extMethodsWithAppliedReceiver = availableExtMethods.flatMap {
+        case (symbol, termName) =>
+          if symbol.is(ExtensionMethod) && !qual.tpe.isBottomType then
+            tryApplyingReceiver(symbol).map(_.copy(name = termName))
+          else None
       }
 
       for (symbol <- extMethodsWithAppliedReceiver) do add(symbol, symbol.name)

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

@@ -2133,8 +2133,34 @@ trait Applications extends Compatibility {
     }
   }
 
-  def isApplicableExtensionMethod(ref: TermRef, receiver: Type)(using Context) =
-    ref.symbol.is(ExtensionMethod)
-    && !receiver.isBottomType
-    && isApplicableMethodRef(ref, receiver :: Nil, WildcardType)
+  private def tryApplyingReceiverToTruncatedExtMethod(methodSym: TermSymbol, receiver: Tree)(using Context): scala.util.Try[Tree] =
+    // Drop all parameters sections of an extension method following the receiver to prevent them from being inferred by the typer
+    def truncateExtension(tp: Type): Type = tp match
+      case poly: PolyType => poly.newLikeThis(poly.paramNames, poly.paramInfos, truncateExtension(poly.resType))
+      case meth: MethodType if meth.isContextualMethod => meth.newLikeThis(meth.paramNames, meth.paramInfos, truncateExtension(meth.resType))
+      case meth: MethodType => meth.newLikeThis(meth.paramNames, meth.paramInfos, defn.AnyType)
+
+    val truncatedSym = methodSym.copy(owner = defn.RootPackage, name = Names.termName(""), info = truncateExtension(methodSym.info))
+    val truncatedRef = ref(truncatedSym).withSpan(Span(0, 0)) // Fake span needed to make this work in REPL
+    val newCtx = ctx.fresh.setNewScope.setReporter(new reporting.ThrowingReporter(ctx.reporter))
+    scala.util.Try {
+      inContext(newCtx) {
+        ctx.enter(truncatedSym)
+        ctx.typer.extMethodApply(truncatedRef, receiver, WildcardType)
+      }
+    }.filter(tree => tree.tpe.exists && !tree.tpe.isError)
+
+  def tryApplyingReceiver(methodSym: TermSymbol, receiver: Tree)(using Context): Option[Tree] =
+    def replaceAppliedRef(inTree: Tree, replacement: Tree)(using Context): Tree = inTree match
+      case Apply(fun, args) => Apply(replaceAppliedRef(fun, replacement), args)
+      case TypeApply(fun, args) => TypeApply(replaceAppliedRef(fun, replacement), args)
+      case _: Ident => replacement
+
+    tryApplyingReceiverToTruncatedExtMethod(methodSym, receiver)
+      .toOption
+      .map(tree => replaceAppliedRef(tree, ref(methodSym)))
+
+  def isApplicableExtensionMethod(ref: TermRef, receiverType: Type)(using Context) =
+    ref.symbol.is(ExtensionMethod) && !receiverType.isBottomType &&
+      tryApplyingReceiverToTruncatedExtMethod(ref.symbol.asTerm, Typed(EmptyTree, TypeTree(receiverType))).isSuccess
 }

language-server/test/dotty/tools/languageserver/CompletionTest.scala

@@ -308,40 +308,140 @@ class CompletionTest {
 
   @Test def completeExtensionMethodWithTypeParameter: Unit = {
     code"""object Foo
-          |extension [A](foo: Foo.type) def xxxx: Int = 1
+          |extension (foo: Foo.type) def xxxx[A]: Int = 1
           |object Main { Foo.xx${m1} }""".withSource
       .completion(m1, Set(("xxxx", Method, "[A] => Int")))
   }
 
   @Test def completeExtensionMethodWithParameterAndTypeParameter: Unit = {
     code"""object Foo
-          |extension [A](foo: Foo.type) def xxxx(a: A) = a
+          |extension (foo: Foo.type) def xxxx[A](a: A) = a
           |object Main { Foo.xx${m1} }""".withSource
       .completion(m1, Set(("xxxx", Method, "[A](a: A): A")))
   }
 
-  @Test def completeExtensionMethodFromExtenionWithAUsingSection: Unit = {
+  @Test def completeExtensionMethodFromExtensionWithTypeParameter: Unit = {
+    code"""extension [A](a: A) def xxxx: A = a
+          |object Main { "abc".xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> String")))
+  }
+
+  @Test def completeExtensionMethodWithResultTypeDependantOnReceiver: Unit = {
+    code"""trait Foo { type Out; def get: Out}
+          |object Bar extends Foo { type Out = String; def get: Out = "abc"}
+          |extension (foo: Foo) def xxxx: foo.Out = foo.get
+          |object Main { Bar.xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> String")))
+  }
+
+  @Test def completeExtensionMethodFromExtenionWithPrefixUsingSection: Unit = {
     code"""object Foo
           |trait Bar
           |trait Baz
-          |given Bar = new Bar {}
-          |given Baz = new Baz {}
+          |given Bar with {}
+          |given Baz with {}
+          |extension (using Bar, Baz)(foo: Foo.type) def xxxx = 1
+          |object Main { Foo.xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> Int")))
+  }
+
+  @Test def completeExtensionMethodFromExtenionWithMultiplePrefixUsingSections: Unit = {
+    code"""object Foo
+          |trait Bar
+          |trait Baz
+          |given Bar with {}
+          |given Baz with {}
+          |extension (using Bar)(using Baz)(foo: Foo.type) def xxxx = 1
+          |object Main { Foo.xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> Int")))
+  }
+
+  @Test def dontCompleteExtensionMethodFromExtenionWithMissingImplicitFromPrefixUsingSection: Unit = {
+    code"""object Foo
+          |trait Bar
+          |trait Baz
+          |given Baz with {}
+          |extension (using Bar, Baz)(foo: Foo.type) def xxxx = 1
+          |object Main { Foo.xx${m1} }""".withSource
+      .completion(m1, Set())
+  }
+
+  @Test def completeExtensionMethodForReceiverOfTypeDependentOnLeadingImplicits: Unit = {
+    code"""
+          |trait Foo:
+          |  type Out <: Bar
+          |
+          |given Foo with
+          |  type Out = Baz
+          |
+          |trait Bar:
+          |  type Out
+          |
+          |trait Baz extends Bar
+          |
+          |given Baz with
+          |  type Out = Quux
+          |
+          |class Quux
+          |
+          |object Quux:
+          |  extension (using foo: Foo)(using fooOut: foo.Out)(fooOutOut: fooOut.Out) def xxxx = "abc"
+          |
+          |object Main { (new Quux).xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> String")))
+  }
+
+  @Test def completeExtensionMethodWithResultTypeDependentOnLeadingImplicit: Unit = {
+    code"""object Foo
+          |trait Bar { type Out; def get: Out }
+          |given Bar with { type Out = 123; def get: Out = 123 }
+          |extension (using bar: Bar)(foo: Foo.type) def xxxx: bar.Out = bar.get
+          |object Main { Foo.xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "=> (123 : Int)")))
+  }
+
+  @Test def completeExtensionMethodFromExtenionWithPostfixUsingSection: Unit = {
+    code"""object Foo
+          |trait Bar
+          |trait Baz
+          |given Bar with {}
+          |given Baz with {}
           |extension (foo: Foo.type)(using Bar, Baz) def xxxx = 1
           |object Main { Foo.xx${m1} }""".withSource
       .completion(m1, Set(("xxxx", Method, "(using x$2: Bar, x$3: Baz): Int")))
   }
 
-  @Test def completeExtensionMethodFromExtenionWithMultipleUsingSections: Unit = {
+  @Test def completeExtensionMethodFromExtenionWithMultiplePostfixUsingSections: Unit = {
     code"""object Foo
           |trait Bar
           |trait Baz
-          |given Bar = new Bar {}
-          |given Baz = new Baz {}
+          |given Bar with {}
+          |given Baz with {}
           |extension (foo: Foo.type)(using Bar)(using Baz) def xxxx = 1
           |object Main { Foo.xx${m1} }""".withSource
       .completion(m1, Set(("xxxx", Method, "(using x$2: Bar)(using x$3: Baz): Int")))
   }
 
+  @Test def completeExtensionMethodWithTypeParameterFromExtenionWithTypeParametersAndPrefixAndPostfixUsingSections: Unit = {
+    code"""trait Bar
+          |trait Baz
+          |given Bar with {}
+          |given Baz with {}
+          |extension [A](using bar: Bar)(a: A)(using baz: Baz) def xxxx[B]: Either[A, B] = Left(a)
+          |object Main { 123.xx${m1} }""".withSource
+      .completion(m1, Set(("xxxx", Method, "(using baz: Baz): [B] => Either[Int, B]")))
+  }
+
+  @Test def completeExtensionMethodWithTypeBounds: Unit = {
+    code"""trait Foo
+          |trait Bar extends Foo
+          |given Bar with {}
+          |extension [A >: Bar](a: A) def xxxx[B <: a.type]: Either[A, B] = Left(a)
+          |val foo = new Foo {}
+          |object Main { foo.xx${m1} }""".withSource
+          .completion(m1, Set(("xxxx", Method, "[B <: (foo : Foo)] => Either[Foo, B]")))
+  }
+
   @Test def completeInheritedExtensionMethod: Unit = {
     code"""object Foo
           |trait FooOps {
@@ -442,10 +542,9 @@ class CompletionTest {
       .completion(m1, Set(("xxxx", Method, "=> Int")))
   }
 
-  @Test def dontCompleteInapplicableExtensionMethod: Unit = {
-    code"""case class Foo[A](a: A)
-          |extension (foo: Foo[Int]) def xxxx = foo.a
-          |object Main { Foo("abc").xx${m1} }""".withSource
+  @Test def dontCompleteExtensionMethodWithMismatchedReceiverType: Unit = {
+    code"""extension (i: Int) def xxxx = i
+          |object Main { "abc".xx${m1} }""".withSource
       .completion(m1, Set())
   }
 }

tests/neg/missing-implicit6.check

@@ -0,0 +1,39 @@
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:34:8 ------------------------------------------------------
+34 |    "a".xxx // error, no suggested import
+   |    ^^^^^^^
+   |    value xxx is not a member of String
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:35:8 ------------------------------------------------------
+35 |    123.xxx // error, suggested import
+   |    ^^^^^^^
+   |    value xxx is not a member of Int, but could be made available as an extension method.
+   |
+   |    The following import might fix the problem:
+   |
+   |      import Test.Ops.xxx
+   |
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:36:8 ------------------------------------------------------
+36 |    123.yyy // error, suggested import
+   |    ^^^^^^^
+   |    value yyy is not a member of Int, but could be made available as an extension method.
+   |
+   |    The following import might fix the problem:
+   |
+   |      import Test.Ops.yyy
+   |
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:41:8 ------------------------------------------------------
+41 |    123.xxx // error, no suggested import
+   |    ^^^^^^^
+   |    value xxx is not a member of Int
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:42:8 ------------------------------------------------------
+42 |    123.yyy // error, no suggested import
+   |    ^^^^^^^
+   |    value yyy is not a member of Int
+-- [E008] Not Found Error: tests/neg/missing-implicit6.scala:43:8 ------------------------------------------------------
+43 |    123.zzz // error, suggested import even though there's no instance of Bar in scope
+   |    ^^^^^^^
+   |    value zzz is not a member of Int, but could be made available as an extension method.
+   |
+   |    The following import might fix the problem:
+   |
+   |      import Test.Ops.zzz
+   |

tests/neg/missing-implicit6.scala

@@ -0,0 +1,45 @@
+trait Foo {
+  type Out <: { type Out }
+}
+
+trait Bar {
+  type Out
+}
+
+object instances {
+  given foo: Foo with {
+    type Out = Bar
+  }
+
+  given bar: Bar with {
+    type Out = Int
+  }
+}
+
+object Test {
+  object Ops {
+    extension (using foo: Foo, bar: foo.Out)(i: Int)
+      def xxx = ???
+
+    extension (using foo: Foo, fooOut: foo.Out)(x: fooOut.Out)
+      def yyy = ???
+
+    extension (using foo: Foo)(i: Int)(using fooOut: foo.Out)
+      def zzz = ???
+  }
+
+  locally {
+    import instances.given
+
+    "a".xxx // error, no suggested import
+    123.xxx // error, suggested import
+    123.yyy // error, suggested import
+  }
+
+  locally {
+    import instances.foo
+    123.xxx // error, no suggested import
+    123.yyy // error, no suggested import
+    123.zzz // error, suggested import even though there's no instance of Bar in scope
+  }
+}