SI-4827 Corrected positions assigned to constructor's default arg

* Default arguments are always retained on the <init> method (i.e.,
  the class' constructor). Therefore, when the <init> parameters are
  created, we need to use `duplicateAndKeepPositions` to make sure that
  if a default argument is present, its opaque position is retained as
  well. This is necessary because when parameter accessors (i.e.,
  `fieldDefs`) are created, all default arguments are discared ( as you
  can see in the code, the right-hand-side of a `field` is always an
  `EmptyTree`) - see changes in TreeGen.scala

* When constructing the `fieldDefs`, it is important to adapt their
  range position to avoid overlappings with the positions of default
  arguments. It is worth noting that updating the field's end position
  to `vd.rhs.pos.start` would be incorrect, because `askTypeAt(pos)`
  could return the incorrect tree when the position is equal to
  `vd.rhs.pos.start` (because two nodes including that point position
  would exist in the tree, and `CompilerControl.locateTree(pos)` would
  return the first tree that includes the passed `pos`). This is why
  `1` is subtracted to `vd.rhs.pos.start`. Alternatively, we could have
  used `vd.tpt.pos.end` with similar results. However the logic would
  have become slightly more complex as we would need to handle the case
  where `vd.tpt` doesn't have a range position (for instance, this can
  happen if `-Yinfer-argument-types` is enabled). Therefore, subtracting
  `1` from `vd.rhs.pos.start` seemed the cleanest solution at the
  moment. - see changes in TreeGen.scala.

* If the synthetic constructor contains trees with an opaque range
  position (see point above), it must have a transparent position.
  This can only happen if the constructor's parameters' positions are
  considered, which is why we are now passing `vparamss1` to
  `wrappingPos` - see changes in TreeGen.scala.

* The derived primary constructor should have a transparent position
  as it may contain trees with an opaque range position. Hence, the
  `primaryCtor` position is considered for computing the position of the
  derived constructor - see change in Typers.scala.

Finally, below follows the printing of the tree for test t4287, which
you should compare with the one attached with the previous commit
message:

```
[[syntax trees at end of typer]] // Foo.scala
[0:63]package [0:0]<empty> {
  [0:37]class Baz extends [9:37][39]scala.AnyRef {
    [10:20]<paramaccessor> private[this] val f: [14]Int = _;
    [14]<stable> <accessor> <paramaccessor> def f: [14]Int = [14][14]Baz.this.f;
    <10:31>def <init>(<10:31>f: [17]<type: [17]scala.Int> = [23:31]B.a): [9]Baz = <10:31>{
      <10:31><10:31><10:31>Baz.super.<init>();
      <10:31>()
    }
  };
  [6]<synthetic> object Baz extends [6][6]AnyRef {
    [6]def <init>(): [9]Baz.type = [6]{
      [6][6][6]Baz.super.<init>();
      [9]()
    };
    [14]<synthetic> def <init>$default$1: [14]Int = [30]B.a
  };
  [39:63]object B extends [48:63][63]scala.AnyRef {
    [63]def <init>(): [48]B.type = [63]{
      [63][63][63]B.super.<init>();
      [48]()
    };
    [52:61]private[this] val a: [56]Int = [60:61]2;
    [56]<stable> <accessor> def a: [56]Int = [56][56]B.this.a
  }
}
```

You should notice that the default arg of `Baz` constructor now has a
range position. And that explains why the associated test now returns
the right tree when asking hyperlinking at the location of the default
argument.

5 files changed, 28 insertions, 4 deletions

diff --git a/test/files/presentation/t4287.check b/test/files/presentation/t4287.check
index 80c3e2fb23..a922421e18 100644
--- a/test/files/presentation/t4287.check
+++ b/test/files/presentation/t4287.check
@@ -1,11 +1,11 @@
 reload: Foo.scala
 
-askHyperlinkPos for `f ` at (1,24) Foo.scala
+askHyperlinkPos for `B` at (1,24) Foo.scala
 ================================================================================
-[response] found askHyperlinkPos for `f ` at (1,15) Foo.scala
+[response] found askHyperlinkPos for `B` at (3,8) Foo.scala
 ================================================================================
 
-askHyperlinkPos for `f ` at (1,31) Foo.scala
+askHyperlinkPos for `a` at (1,31) Foo.scala
 ================================================================================
-[response] found askHyperlinkPos for `f ` at (1,15) Foo.scala
+[response] found askHyperlinkPos for `a` at (4,7) Foo.scala
 ================================================================================
diff --git a/test/files/presentation/t4287c.check b/test/files/presentation/t4287c.check
new file mode 100644
index 0000000000..42fc30997d
--- /dev/null
+++ b/test/files/presentation/t4287c.check
@@ -0,0 +1,11 @@
+reload: Foo.scala
+
+askHyperlinkPos for `A` at (1,18) Foo.scala
+================================================================================
+[response] found askHyperlinkPos for `A` at (3,8) Foo.scala
+================================================================================
+
+askHyperlinkPos for `a` at (1,25) Foo.scala
+================================================================================
+[response] found askHyperlinkPos for `a` at (4,7) Foo.scala
+================================================================================
diff --git a/test/files/presentation/t4287c.flags b/test/files/presentation/t4287c.flags
new file mode 100644
index 0000000000..d1a8244169
--- /dev/null
+++ b/test/files/presentation/t4287c.flags
@@ -0,0 +1 @@
+-Yinfer-argument-types
\ No newline at end of file
diff --git a/test/files/presentation/t4287c/Test.scala b/test/files/presentation/t4287c/Test.scala
new file mode 100644
index 0000000000..bec1131c4c
--- /dev/null
+++ b/test/files/presentation/t4287c/Test.scala
@@ -0,0 +1,3 @@
+import scala.tools.nsc.interactive.tests.InteractiveTest
+
+object Test extends InteractiveTest
\ No newline at end of file
diff --git a/test/files/presentation/t4287c/src/Foo.scala b/test/files/presentation/t4287c/src/Foo.scala
new file mode 100644
index 0000000000..26870b5021
--- /dev/null
+++ b/test/files/presentation/t4287c/src/Foo.scala
@@ -0,0 +1,9 @@
+class A(a: Int = A/*#*/.a/*#*/)
+
+object A {
+  val a = 2
+}
+
+class B extends A {
+ def this(a) = this()
+}
\ No newline at end of file