Fix #8875: Make detection of extension methods work over all phases

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -22,6 +22,7 @@ import TypeApplications._
 import Decorators._
 import scala.internal.Chars.isOperatorPart
 import transform.TypeUtils._
+import transform.SymUtils._
 
 import language.implicitConversions
 import dotty.tools.dotc.util.{NameTransformer, SourcePosition}
@@ -784,7 +785,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     import untpd._
     dclTextOr(tree) {
       val defKeyword = modText(tree.mods, tree.symbol, keywordStr("def"), isType = false)
-      val isExtension = tree.hasType && tree.symbol.is(Extension)
+      val isExtension = tree.hasType && tree.symbol.isExtensionMethod
       withEnclosingDef(tree) {
         val (prefix, vparamss) =
           if (isExtension) (defKeyword ~~ paramsText(tree.vparamss.head) ~~ valDefText(nameIdText(tree)), tree.vparamss.tail)

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

@@ -212,8 +212,15 @@ class SymUtils(val self: Symbol) extends AnyVal {
   def isSplice(implicit ctx: Context): Boolean =
     self == defn.InternalQuoted_exprSplice || self == defn.InternalQuoted_exprNestedSplice || self == defn.QuotedType_splice
 
+  /** Is symbol an extension method? Accessors are excluded since
+   *  after the getters phase collective extension objects become accessors
+   */
+  def isExtensionMethod(using Context): Boolean =
+    self.isAllOf(ExtensionMethod, butNot = Accessor)
+
+  /** Is symbol the module class of a collective extension object? */
   def isCollectiveExtensionClass(using Context): Boolean =
-    self.is(ModuleClass) && self.sourceModule.is(Extension, butNot = Method)
+    self.is(ModuleClass) && self.sourceModule.is(Extension) && !self.sourceModule.isExtensionMethod
 
   def isScalaStatic(using Context): Boolean =
     self.hasAnnotation(ctx.definitions.ScalaStaticAnnot)

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -64,6 +64,7 @@ class CompilationTests extends ParallelTesting {
       compileFile("tests/pos-special/kind-projector.scala", defaultOptions.and("-Ykind-projector")),
       compileFile("tests/run/i5606.scala", defaultOptions.and("-Yretain-trees")),
       compileFile("tests/pos-custom-args/i5498-postfixOps.scala", defaultOptions withoutLanguageFeature "postfixOps"),
+      compileFile("tests/pos-custom-args/i8875.scala", defaultOptions.and("-Xprint:getters")),
     ).checkCompile()
   }
 

tests/pos-custom-args/i8875.scala

@@ -0,0 +1,5 @@
+class A {
+  extension Ext on (a: Int) {
+    def foo: Int = 1
+  }
+}