Better error reporting regarding main methods.

Now notices most things which look like main methods and says
something useful if they aren't usable as entry points.
Closes SI-4749.

4 files changed, 83 insertions, 10 deletions

diff --git a/test/files/neg/main1.check b/test/files/neg/main1.check
index 734c78e54d..1a7a13e1e9 100644
--- a/test/files/neg/main1.check
+++ b/test/files/neg/main1.check
@@ -1,25 +1,25 @@
-main1.scala:3: error: Foo has a main method, but foo1.Foo will not be a runnable program.
-  Its companion is a trait, which means no static forwarder can be generated.
+main1.scala:3: error: Foo has a main method with parameter type Array[String], but foo1.Foo will not be a runnable program.
+  Reason: companion is a trait, which means no static forwarder can be generated.
 
   object Foo {  // companion is trait
          ^
-main1.scala:10: error: Foo has a main method, but foo2.Foo will not be a runnable program.
-  Its companion contains its own main method, which means no static forwarder can be generated.
+main1.scala:10: error: Foo has a main method with parameter type Array[String], but foo2.Foo will not be a runnable program.
+  Reason: companion contains its own main method, which means no static forwarder can be generated.
 
   object Foo {  // companion has its own main
          ^
-main1.scala:22: error: Foo has a main method, but foo3.Foo will not be a runnable program.
-  Its companion contains its own main method (implementation restriction: no main is allowed, regardless of signature), which means no static forwarder can be generated.
+main1.scala:22: error: Foo has a main method with parameter type Array[String], but foo3.Foo will not be a runnable program.
+  Reason: companion contains its own main method (implementation restriction: no main is allowed, regardless of signature), which means no static forwarder can be generated.
 
   object Foo {  // Companion contains main, but not an interfering main.
          ^
-main1.scala:31: error: Foo has a main method, but foo4.Foo will not be a runnable program.
-  Its companion contains its own main method (implementation restriction: no main is allowed, regardless of signature), which means no static forwarder can be generated.
+main1.scala:31: error: Foo has a main method with parameter type Array[String], but foo4.Foo will not be a runnable program.
+  Reason: companion contains its own main method, which means no static forwarder can be generated.
 
   object Foo extends Foo {  // Inherits main from the class
          ^
-main1.scala:39: error: Foo has a main method, but foo5.Foo will not be a runnable program.
-  Its companion contains its own main method (implementation restriction: no main is allowed, regardless of signature), which means no static forwarder can be generated.
+main1.scala:39: error: Foo has a main method with parameter type Array[String], but foo5.Foo will not be a runnable program.
+  Reason: companion contains its own main method, which means no static forwarder can be generated.
 
   object Foo extends Foo {  // Overrides main from the class
          ^
diff --git a/test/files/neg/t4749.check b/test/files/neg/t4749.check
new file mode 100644
index 0000000000..93ad3935fa
--- /dev/null
+++ b/test/files/neg/t4749.check
@@ -0,0 +1,28 @@
+t4749.scala:2: error: Fail1 has a main method with parameter type Array[String], but bippy.Fail1 will not be a runnable program.
+  Reason: main method must have exact signature (Array[String])Unit
+  object Fail1 {
+         ^
+t4749.scala:6: error: Fail2 has a main method with parameter type Array[String], but bippy.Fail2 will not be a runnable program.
+  Reason: main methods cannot be generic.
+  object Fail2 {
+         ^
+t4749.scala:13: error: Fail3 has a main method with parameter type Array[String], but bippy.Fail3 will not be a runnable program.
+  Reason: main methods cannot refer to type parameters or abstract types.
+  object Fail3 extends Bippy[Unit] { }
+         ^
+t4749.scala:16: error: Fail4 has a main method with parameter type Array[String], but bippy.Fail4 will not be a runnable program.
+  Reason: companion is a trait, which means no static forwarder can be generated.
+
+  object Fail4 {
+         ^
+t4749.scala:21: error: Fail5 has a main method with parameter type Array[String], but bippy.Fail5 will not be a runnable program.
+  Reason: companion contains its own main method, which means no static forwarder can be generated.
+
+  object Fail5 extends Fail5 { }    
+         ^
+t4749.scala:26: error: Fail6 has a main method with parameter type Array[String], but bippy.Fail6 will not be a runnable program.
+  Reason: companion contains its own main method (implementation restriction: no main is allowed, regardless of signature), which means no static forwarder can be generated.
+
+  object Fail6 {
+         ^
+6 errors found
diff --git a/test/files/neg/t4749.flags b/test/files/neg/t4749.flags
new file mode 100644
index 0000000000..e8fb65d50c
--- /dev/null
+++ b/test/files/neg/t4749.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/neg/t4749.scala b/test/files/neg/t4749.scala
new file mode 100644
index 0000000000..0973c36097
--- /dev/null
+++ b/test/files/neg/t4749.scala
@@ -0,0 +1,44 @@
+package bippy {
+  object Fail1 {
+    def main(args: Array[String]): Any = ()
+  }
+
+  object Fail2 {
+    def main[T](args: Array[String]): T = null.asInstanceOf[T]
+  }
+
+  abstract class Bippy[T] {
+    def main(args: Array[String]): T = null.asInstanceOf[T]
+  }
+  object Fail3 extends Bippy[Unit] { }
+
+
+  object Fail4 {
+    def main(args: Array[String]): Unit = ()
+  }
+  trait Fail4 { }
+
+  object Fail5 extends Fail5 { }    
+  class Fail5 {
+    def main(args: Array[String]): Unit = ()
+  }
+
+  object Fail6 {
+    def main(args: Array[String]): Unit = ()
+  }
+  class Fail6 {
+    def main = "bippy"
+  }
+
+  object Win1 {
+    def main(args: Array[String]): Unit = ()
+  }
+  object Win2 extends Bippy[Unit] {
+    override def main(args: Array[String]): Unit = ()
+  }
+  trait WinBippy[T] {
+    def main(args: Array[String]): T = null.asInstanceOf[T]
+  }
+  object Win3 extends WinBippy[Unit] { }
+}
+