Fix #9100: Add error when experimental macros are not enabled

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -60,6 +60,9 @@ object Feature:
   def dependentEnabled(using Context) =
     enabled(nme.dependent, defn.LanguageExperimentalModule.moduleClass)
 
+  def scala2ExperimentalMacroEnabled(using Context) =
+    enabled("macros".toTermName, defn.LanguageExperimentalModule.moduleClass)
+
   def sourceVersionSetting(using Context): SourceVersion =
     SourceVersion.valueOf(ctx.settings.source.value)
 

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

@@ -3581,6 +3581,16 @@ class Typer extends Namer
       }
     }
     if ctx.phase.isTyper then
+      call match
+        case untpd.Ident(nme.???) => // Instinsic macros ignored
+        case _ =>
+          if !config.Feature.scala2ExperimentalMacroEnabled then
+            ctx.error(
+              """Scala 2 macro definition needs to be enabled
+                |by making the implicit value scala.language.experimental.macros visible.
+                |This can be achieved by adding the import clause 'import scala.language.experimental.macros'
+                |or by setting the compiler option -language:experimental.macros.
+              """.stripMargin, call.sourcePos)
       call match
         case call: untpd.Ident =>
           typedIdent(call, defn.AnyType)

tests/neg/i9100.scala

@@ -0,0 +1,3 @@
+object FooMacros {
+  def foo[T]: String = macro Foo.fooImpl[T] // error: Scala 2 macro definition needs to be enabled
+}

tests/semanticdb/expect/Classes.expect.scala

@@ -1,5 +1,5 @@
 package classes
-
+import scala.language/*->scalaShadowing::language.*/.experimental/*->scalaShadowing::language.experimental.*/.macros/*->scalaShadowing::language.experimental.macros.*/
 class C1/*<-classes::C1#*/(val x1/*<-classes::C1#x1.*/: Int/*->scala::Int#*/) extends AnyVal/*->scala::AnyVal#*//*->scala::AnyVal#`<init>`().*/
 
 class C2/*<-classes::C2#*/(val x2/*<-classes::C2#x2.*/: Int/*->scala::Int#*/) extends AnyVal/*->scala::AnyVal#*//*->scala::AnyVal#`<init>`().*/

tests/semanticdb/expect/Classes.scala

@@ -1,5 +1,5 @@
 package classes
-
+import scala.language.experimental.macros
 class C1(val x1: Int) extends AnyVal
 
 class C2(val x2: Int) extends AnyVal

tests/semanticdb/metac.expect

@@ -340,7 +340,7 @@ Uri => Classes.scala
 Text => empty
 Language => Scala
 Symbols => 106 entries
-Occurrences => 126 entries
+Occurrences => 130 entries
 
 Symbols:
 classes/C1# => final class C1
@@ -452,6 +452,10 @@ local3 => val local local
 
 Occurrences:
 [0:8..0:15): classes <- classes/
+[1:7..1:12): scala -> scala/
+[1:13..1:21): language -> scalaShadowing/language.
+[1:22..1:34): experimental -> scalaShadowing/language.experimental.
+[1:35..1:41): macros -> scalaShadowing/language.experimental.macros.
 [2:6..2:8): C1 <- classes/C1#
 [2:8..2:21): <- classes/C1#`<init>`().
 [2:13..2:15): x1 <- classes/C1#x1.