From 6a417ea00be361f663b38f35fc558dcc15109afd Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Thu, 6 Feb 2025 01:08:48 -0800
Subject: [PATCH] Forward reference error includes line numbers

---
 .../dotty/tools/dotc/reporting/messages.scala |  5 +-
 tests/neg/i14401.check                        | 30 ++++++++++++
 tests/neg/i14401.scala                        | 46 +++++++++++++++++++
 tests/untried/neg/forward.check               | 10 ----
 tests/untried/neg/forward.scala               | 24 ----------
 5 files changed, 80 insertions(+), 35 deletions(-)
 create mode 100644 tests/neg/i14401.check
 create mode 100644 tests/neg/i14401.scala
 delete mode 100644 tests/untried/neg/forward.check
 delete mode 100644 tests/untried/neg/forward.scala

diff --git a/compiler/src/dotty/tools/dotc/reporting/messages.scala b/compiler/src/dotty/tools/dotc/reporting/messages.scala
index 56420a0e0bc2..ac72ee4aa21f 100644
--- a/compiler/src/dotty/tools/dotc/reporting/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/messages.scala
@@ -1190,7 +1190,10 @@ extends DeclarationMsg(OverrideErrorID), NoDisambiguation:
 
 class ForwardReferenceExtendsOverDefinition(value: Symbol, definition: Symbol)(using Context)
 extends ReferenceMsg(ForwardReferenceExtendsOverDefinitionID) {
-  def msg(using Context) = i"${definition.name} is a forward reference extending over the definition of ${value.name}"
+  extension (sym: Symbol) def srcLine = sym.line + 1
+  def msg(using Context) = i"${definition.name}${
+    if value != definition then s" (defined on L${definition.srcLine})" else ""
+  } is a forward reference extending over the definition of ${value.name} (on L${value.srcLine})"
 
   def explain(using Context) =
     i"""|${definition.name} is used before you define it, and the definition of ${value.name}
diff --git a/tests/neg/i14401.check b/tests/neg/i14401.check
new file mode 100644
index 000000000000..929dbf3dac59
--- /dev/null
+++ b/tests/neg/i14401.check
@@ -0,0 +1,30 @@
+-- [E039] Reference Error: tests/neg/i14401.scala:6:17 -----------------------------------------------------------------
+6 |    def f: Int = x; // error
+  |                 ^
+  |                 x is a forward reference extending over the definition of x (on L7)
+  |
+  | longer explanation available when compiling with `-explain`
+-- [E039] Reference Error: tests/neg/i14401.scala:10:17 ----------------------------------------------------------------
+10 |    def f: Int = g; // error
+   |                 ^
+   |                 g (defined on L12) is a forward reference extending over the definition of x (on L11)
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E039] Reference Error: tests/neg/i14401.scala:15:17 ----------------------------------------------------------------
+15 |    def f: Int = g; // error
+   |                 ^
+   |                 g (defined on L17) is a forward reference extending over the definition of x (on L16)
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E039] Reference Error: tests/neg/i14401.scala:31:15 ----------------------------------------------------------------
+31 |      } yield a // error
+   |               ^
+   |               ec (defined on L33) is a forward reference extending over the definition of z (on L29)
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E039] Reference Error: tests/neg/i14401.scala:41:28 ----------------------------------------------------------------
+41 |    class NotUsed {val xs = args} // error
+   |                            ^^^^
+   |                    args (defined on L44) is a forward reference extending over the definition of dummy (on L42)
+   |
+   | longer explanation available when compiling with `-explain`
diff --git a/tests/neg/i14401.scala b/tests/neg/i14401.scala
new file mode 100644
index 000000000000..a9be93cad998
--- /dev/null
+++ b/tests/neg/i14401.scala
@@ -0,0 +1,46 @@
+object Test {
+  def f: Int = x;
+  val x: Int = f;
+
+  {
+    def f: Int = x; // error
+    val x: Int = f;
+  }
+  {
+    def f: Int = g; // error
+    val x: Int = f;
+    def g: Int = x;
+  }
+  {
+    def f: Int = g; // error
+    var x: Int = f;
+    def g: Int = x;
+  }
+  {
+    def f: Int = g;
+    Console.println("foo");
+    def g: Int = f;
+  }
+  {
+    import scala.concurrent.{ExecutionContext, Future}, ExecutionContext.Implicits
+
+    def foo: Future[Int] = {
+      val fInt = Future.successful(1)
+      val z = for {
+        a <- fInt
+      } yield a // error
+
+      implicit val ec: ExecutionContext = Implicits.global
+      z
+    }
+    foo
+  }
+}
+object MyApp {
+  def main(args: Array[String]) = {
+    class NotUsed {val xs = args} // error
+    val dummy = false
+    // oops, shadows the parameter
+    def args = Seq("a","b","c")
+  }
+}
diff --git a/tests/untried/neg/forward.check b/tests/untried/neg/forward.check
deleted file mode 100644
index 252c990370e0..000000000000
--- a/tests/untried/neg/forward.check
+++ /dev/null
@@ -1,10 +0,0 @@
-forward.scala:6: error: forward reference extends over definition of value x
-    def f: Int = x;
-                 ^
-forward.scala:10: error: forward reference extends over definition of value x
-    def f: Int = g;
-                 ^
-forward.scala:15: error: forward reference extends over definition of variable x
-    def f: Int = g;
-                 ^
-three errors found
diff --git a/tests/untried/neg/forward.scala b/tests/untried/neg/forward.scala
deleted file mode 100644
index d5c0851f09e3..000000000000
--- a/tests/untried/neg/forward.scala
+++ /dev/null
@@ -1,24 +0,0 @@
-object Test {
-  def f: Int = x;
-  val x: Int = f;
-
-  {
-    def f: Int = x;
-    val x: Int = f;
-  }
-  {
-    def f: Int = g;
-    val x: Int = f;
-    def g: Int = x;
-  }
-  {
-    def f: Int = g;
-    var x: Int = f;
-    def g: Int = x;
-  }
-  {
-    def f: Int = g;
-    Console.println("foo");
-    def g: Int = f;
-  }
-}