feat: add in an action for missing empty argument list

Author: ckipp01

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -32,6 +32,7 @@ import cc.CaptureSet.IdentityCaptRefMap
 import dotty.tools.dotc.rewrites.Rewrites.ActionPatch
 import dotty.tools.dotc.util.Spans.Span
 import dotty.tools.dotc.util.SourcePosition
+import scala.jdk.CollectionConverters.*
 
 /** Messages
  * ========
@@ -1858,8 +1859,6 @@ class OnlyFunctionsCanBeFollowedByUnderscore(tp: Type, tree: untpd.PostfixOp)(us
 
  override def actions(using Context) =
  val untpd.PostfixOp(qual, Ident(nme.WILDCARD)) = tree: @unchecked
- import scala.language.unsafeNulls
- import scala.jdk.CollectionConverters.*
  List(
  CodeAction(title = "Rewrite to function value",
  description = java.util.Optional.empty(),
@@ -1871,7 +1870,7 @@ class OnlyFunctionsCanBeFollowedByUnderscore(tp: Type, tree: untpd.PostfixOp)(us
  ).asJava
 }
 
-class MissingEmptyArgumentList(method: String)(using Context)
+class MissingEmptyArgumentList(method: String, tree: tpd.Tree)(using Context)
  extends SyntaxMsg(MissingEmptyArgumentListID) {
  def msg(using Context) = i"$method must be called with ${hl("()")} argument"
  def explain(using Context) = {
@@ -1886,6 +1885,16 @@ class MissingEmptyArgumentList(method: String)(using Context)
  |In Dotty, this idiom is an error. The application syntax has to follow exactly the parameter syntax.
  |Excluded from this rule are methods that are defined in Java or that override methods defined in Java."""
  }
+
+ override def actions(using Context) =
+ List(
+ CodeAction(title = "Insert ()",
+ description = java.util.Optional.empty(),
+ patches = List(
+ ActionPatch(SourcePosition(tree.source, tree.span.endPos), "()"),
+ ).asJava
+ )
+ ).asJava
 }
 
 class DuplicateNamedTypeParameter(name: Name)(using Context)

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

@@ -55,7 +55,7 @@ object ErrorReporting {
  val meth = err.exprStr(methPart(tree))
  val info = if tree.symbol.exists then tree.symbol.info else mt
  if isCallableWithSingleEmptyArgumentList(info) then
- report.error(MissingEmptyArgumentList(meth), tree.srcPos)
+ report.error(MissingEmptyArgumentList(meth, tree), tree.srcPos)
  else
  report.error(MissingArgumentList(meth, tree.symbol), tree.srcPos)
 

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

@@ -3953,7 +3953,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
  def isAutoApplied(sym: Symbol): Boolean =
  sym.isConstructor
  || sym.matchNullaryLoosely
- || Feature.warnOnMigration(MissingEmptyArgumentList(sym.show), tree.srcPos, version = `3.0`)
+ || Feature.warnOnMigration(MissingEmptyArgumentList(sym.show, tree), tree.srcPos, version = `3.0`)
  && { patch(tree.span.endPos, "()"); true }
 
  /** If this is a selection prototype of the form `.apply(...): R`, return the nested

compiler/test/dotty/tools/dotc/reporting/CodeActionTest.scala

@@ -30,6 +30,20 @@ class CodeActionTest extends DottyTest:
  |""".stripMargin
  )
 
+ @Test def insertBracesForEmptyArgument =
+ checkCodeAction(
+ """|object Test:
+ | def foo(): Unit = ()
+ | val x = foo
+ |""".stripMargin,
+ "Insert ()",
+ """|object Test:
+ | def foo(): Unit = ()
+ | val x = foo()
+ |""".stripMargin
+
+ )
+
  // Make sure we're not using the default reporter, which is the ConsoleReporter,
  // meaning they will get reported in the test run and that's it.
  private def newContext =
@@ -41,11 +55,11 @@ class CodeActionTest extends DottyTest:
  val source = SourceFile.virtual("test", code).content
  val runCtx = checkCompile("typer", code) { (_, _) => () }
  val diagnostics = runCtx.reporter.removeBufferedMessages
- assertEquals(diagnostics.size, 1)
+ assertEquals(1, diagnostics.size)
 
  val diagnostic = diagnostics.head
  val actions = diagnostic.msg.actions.asScala.toList
- assertEquals(actions.size, 1)
+ assertEquals(1, actions.size)
 
  // TODO account for more than 1 action
  val action = actions.head
@@ -80,4 +94,4 @@ class CodeActionTest extends DottyTest:
  assert(outNew == result.length, s"$outNew != ${result.length}")
 
  loop(patches, 0, 0)
- assertEquals(result.mkString, expected)
+ assertEquals(expected, result.mkString)