Collective extensions is sensitive to EOF

This allows REPL to input extensions.

Author: dos65

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

@@ -3652,7 +3652,7 @@ object Parsers {
           in.observeIndented()
           newLineOptWhenFollowedBy(LBRACE)
           if in.isNestedStart then inDefScopeBraces(extMethods(nparams))
-          else { syntaxError("Extension without extension methods"); Nil }
+          else { syntaxErrorOrIncomplete("Extension without extension methods") ; Nil }
       val result = atSpan(start)(ExtMethods(joinParams(tparams, leadParamss.toList), methods))
       val comment = in.getDocComment(start)
       if comment.isDefined then
@@ -3674,10 +3674,15 @@ object Parsers {
     def extMethods(numLeadParams: Int): List[DefDef] = checkNoEscapingPlaceholders {
       val meths = new ListBuffer[DefDef]
       while
-        meths += extMethod(numLeadParams)
-        statSepOrEnd(meths, what = "extension method")
+        val start = in.offset
+        val mods = defAnnotsMods(modifierTokens)
+        in.token != EOF && {
+          accept(DEF)
+          meths += defDefOrDcl(start, mods, numLeadParams)
+          in.token != EOF && statSepOrEnd(meths, what = "extension method")
+        }
       do ()
-      if meths.isEmpty then syntaxError("`def` expected")
+      if meths.isEmpty then syntaxErrorOrIncomplete("`def` expected")
       meths.toList
     }
 

compiler/test/dotty/tools/repl/ReplCompilerTests.scala

@@ -199,6 +199,12 @@ class ReplCompilerTests extends ReplTest {
     assertFalse(ParseResult.isIncomplete("_ + 1"))  // was: assertThrows[NullPointerException]
   }
 
+  @Test def `i9374 accept collective extensions`: Unit = fromInitialState { state =>
+    given Context = state.context
+    assert(ParseResult.isIncomplete("extension (x: String)"))
+    assert(ParseResult.isIncomplete("extension (x: String) {"))
+  }
+
   @Test def testSingletonPrint = fromInitialState { implicit state =>
     run("""val a = "hello"; val x: a.type = a""")
     assertMultiLineEquals("val a: String = hello\nval x: a.type = hello", storedOutput().trim)