Only disallow synthesized lambdas in statement position

odersky · odersky · commit dd10c09d629f · 2021-03-17T10:17:41.000+01:00
For user-written lambdas, presumably the devs know what they are doing. User-written
numbers aappear in quite a lot of test cases.

A second change of this commit is that closure methods now get a more accurate span.
diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -1306,9 +1306,10 @@ object desugar {
    *      def $anonfun(params) = body
    *      Closure($anonfun)
    */
-  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = null, isContextual: Boolean)(using Context): Block =
+  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = null, isContextual: Boolean, span: Span)(using Context): Block =
     Block(
       DefDef(nme.ANON_FUN, params :: Nil, if (tpt == null) TypeTree() else tpt, body)
+        .withSpan(span)
         .withMods(synthetic | Artifact),
       Closure(Nil, Ident(nme.ANON_FUN), if (isContextual) ContextualEmptyTree else EmptyTree))
 
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1356,7 +1356,7 @@ class Typer extends Namer
             else cpy.ValDef(param)(
               tpt = untpd.TypeTree(
                 inferredParamType(param, protoFormal(i)).translateFromRepeated(toArray = false)))
-        desugar.makeClosure(inferredParams, fnBody, resultTpt, isContextual)
+        desugar.makeClosure(inferredParams, fnBody, resultTpt, isContextual, tree.span)
       }
     typed(desugared, pt)
   }
@@ -3830,8 +3830,11 @@ class Typer extends Namer
       && isPureExpr(tree)
       && !isSelfOrSuperConstrCall(tree)
     then tree match
-      case closureDef(_) => missingArgs(tree, tree.tpe.widen)
-      case _ => report.warning(PureExpressionInStatementPosition(original, exprOwner), original.srcPos)
+      case closureDef(meth) if meth.span == meth.rhs.span.toSynthetic =>
+        // it's a synthesized lambda, for instance via an eta expansion: report a hard error
+        missingArgs(tree, tree.tpe.widen)
+      case _ =>
+        report.warning(PureExpressionInStatementPosition(original, exprOwner), original.srcPos)
 
   /** Types the body Scala 2 macro declaration `def f = macro <body>` */
   private def typedScala2MacroBody(call: untpd.Tree)(using Context): Tree =
diff --git a/tests/neg-custom-args/erased/erased-pathdep-1.scala b/tests/neg-custom-args/erased/erased-pathdep-1.scala
@@ -3,8 +3,8 @@
 object Test {
 
   fun1(new Bar)
-  fun2(new Bar)
-  fun3(new Bar)
+  val _ = fun2(new Bar)
+  val _ = fun3(new Bar)
 
   def fun1[F >: Bar <: Foo](erased f: F): f.X = null.asInstanceOf[f.X] // error // error
   def fun2[F >: Bar <: Foo](erased f: F)(erased bar: f.B): f.B = null.asInstanceOf[f.B] // error // error // error
diff --git a/tests/neg/i11671.scala b/tests/neg/i11671.scala
@@ -4,5 +4,5 @@ def go(x: Int): Unit =
   go  // error
 
 def foo: Unit =
-  (x: Int) => go(x) // error
+  (x: Int) => go(x) // warning
 
diff --git a/tests/neg/i5311.check b/tests/neg/i5311.check
@@ -1,7 +1,7 @@
--- [E007] Type Mismatch Error: tests/neg/i5311.scala:11:9 --------------------------------------------------------------
+-- [E007] Type Mismatch Error: tests/neg/i5311.scala:11:8 --------------------------------------------------------------
 11 |    baz((x : s.T[Int]) => x) // error
-   |         ^^^^^^^^^^^^^^^^^^
-   |         Found:    s.T[Int] => s.T[Int]
-   |         Required: m.Foo
+   |        ^^^^^^^^^^^^^^^^^^^
+   |        Found:    s.T[Int] => s.T[Int]
+   |        Required: m.Foo
 
 longer explanation available when compiling with `-explain`
diff --git a/tests/neg/i7359-g.check b/tests/neg/i7359-g.check
@@ -1,7 +1,7 @@
--- [E007] Type Mismatch Error: tests/neg/i7359-g.scala:5:25 ------------------------------------------------------------
+-- [E007] Type Mismatch Error: tests/neg/i7359-g.scala:5:19 ------------------------------------------------------------
 5 |val m : SAMTrait = () => "Hello" // error
-  |                         ^^^^^^^
-  |                         Found:    () => String
-  |                         Required: SAMTrait
+  |                   ^^^^^^^^^^^^^
+  |                   Found:    () => String
+  |                   Required: SAMTrait
 
 longer explanation available when compiling with `-explain`
diff --git a/tests/pos/i3873.scala b/tests/pos/i3873.scala
@@ -1,6 +1,6 @@
 object Test {
   inline def sum2(ys: List[Int]): Unit = {
-    ys.foldLeft(1)
+    val _ = ys.foldLeft(1)
   }
   val h1 = (xs: List[Int]) => sum2(xs)
 }
diff --git a/tests/pos/typedapply.scala b/tests/pos/typedapply.scala
@@ -6,6 +6,6 @@ object typedapply {
 
   foo[Int, String](1, "abc")
 
-  foo[Int, String] _
+  val x = foo[Int, String] _
 
 }

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	`object Test {`
`2`	`2`	`inline def sum2(ys: List[Int]): Unit = {`
`3`		`- ys.foldLeft(1)`
	`3`	`+ val _ = ys.foldLeft(1)`
`4`	`4`	`}`
`5`	`5`	`val h1 = (xs: List[Int]) => sum2(xs)`
`6`	`6`	`}`
Original file line number	Diff line number	Diff line change
`@@ -6,6 +6,6 @@ object typedapply {`
`6`	`6`
`7`	`7`	`foo[Int, String](1, "abc")`
`8`	`8`
`9`		`- foo[Int, String] _`
	`9`	`+ val x = foo[Int, String] _`
`10`	`10`
`11`	`11`	`}`