gdb/tui: add left_boxed_p and right_boxed_p member functions

When I initially saw this code in tui_layout_split::apply, I assumed
that this must be a bug:

    /* Two adjacent boxed windows will share a border, making a bit
       more size available.  */
    if (i > 0
        && m_splits[i - 1].layout->bottom_boxed_p ()
        && m_splits[i].layout->top_boxed_p ())
      ...

After all, the apply might be laying out a horizontal layout, right?
So checking bottom_boxed_p and top_boxed_p is clearly wrong.

Well, it turns on, that due to the implementations of these things,
bottom_boxed_p is equivalent to an imagined right_boxed_p, and
top_boxed_p is equivalent to an imagined left_boxed_p.

In this commit I've renamed both top_boxed_p and bottom_boxed_p to
first_edge_has_border_p and last_edge_has_border_p respectively, and
extended the comments in tui_layout_base to mention that these methods
handle both horizontal and vertical layouts.

Now, hopefully, the code shouldn't look like it only applies for
vertical layouts.

There should be no user visible changes after this commit.

2 files changed, 18 insertions, 16 deletions

diff --git a/gdb/tui/tui-layout.c b/gdb/tui/tui-layout.c
index 6fd176d..c890b86 100644
--- a/gdb/tui/tui-layout.c
+++ b/gdb/tui/tui-layout.c
@@ -451,7 +451,7 @@ tui_layout_window::get_sizes (bool height, int *min_value, int *max_value)
 /* See tui-layout.h.  */
 
 bool
-tui_layout_window::top_boxed_p () const
+tui_layout_window::first_edge_has_border_p () const
 {
   gdb_assert (m_window != nullptr);
   return m_window->can_box ();
@@ -460,7 +460,7 @@ tui_layout_window::top_boxed_p () const
 /* See tui-layout.h.  */
 
 bool
-tui_layout_window::bottom_boxed_p () const
+tui_layout_window::last_edge_has_border_p () const
 {
   gdb_assert (m_window != nullptr);
   return m_window->can_box ();
@@ -561,21 +561,21 @@ tui_layout_split::get_sizes (bool height, int *min_value, int *max_value)
 /* See tui-layout.h.  */
 
 bool
-tui_layout_split::top_boxed_p () const
+tui_layout_split::first_edge_has_border_p () const
 {
   if (m_splits.empty ())
     return false;
-  return m_splits[0].layout->top_boxed_p ();
+  return m_splits[0].layout->first_edge_has_border_p ();
 }
 
 /* See tui-layout.h.  */
 
 bool
-tui_layout_split::bottom_boxed_p () const
+tui_layout_split::last_edge_has_border_p () const
 {
   if (m_splits.empty ())
     return false;
-  return m_splits.back ().layout->top_boxed_p ();
+  return m_splits.back ().layout->last_edge_has_border_p ();
 }
 
 /* See tui-layout.h.  */
@@ -785,8 +785,8 @@ tui_layout_split::apply (int x_, int y_, int width_, int height_)
       /* Two adjacent boxed windows will share a border, making a bit
 	 more size available.  */
       if (i > 0
-	  && m_splits[i - 1].layout->bottom_boxed_p ()
-	  && m_splits[i].layout->top_boxed_p ())
+	  && m_splits[i - 1].layout->last_edge_has_border_p ()
+	  && m_splits[i].layout->first_edge_has_border_p ())
 	info[i].share_box = true;
     }
 
diff --git a/gdb/tui/tui-layout.h b/gdb/tui/tui-layout.h
index 26de3c3..9cfcfb8 100644
--- a/gdb/tui/tui-layout.h
+++ b/gdb/tui/tui-layout.h
@@ -62,11 +62,13 @@ public:
      HEIGHT is true to fetch height, false to fetch width.  */
   virtual void get_sizes (bool height, int *min_value, int *max_value) = 0;
 
-  /* True if the topmost item in this layout is boxed.  */
-  virtual bool top_boxed_p () const = 0;
+  /* True if the topmost (for vertical layouts), or the leftmost (for
+     horizontal layouts) item in this layout is boxed.  */
+  virtual bool first_edge_has_border_p () const = 0;
 
-  /* True if the bottommost item in this layout is boxed.  */
-  virtual bool bottom_boxed_p () const = 0;
+  /* True if the bottommost (for vertical layouts), or the rightmost (for
+     horizontal layouts) item in this layout is boxed.  */
+  virtual bool last_edge_has_border_p () const = 0;
 
   /* Return the name of this layout's window, or nullptr if this
      layout does not represent a single window.  */
@@ -141,9 +143,9 @@ public:
     return m_contents == name ? FOUND : NOT_FOUND;
   }
 
-  bool top_boxed_p () const override;
+  bool first_edge_has_border_p () const override;
 
-  bool bottom_boxed_p () const override;
+  bool last_edge_has_border_p () const override;
 
   void remove_windows (const char *name) override
   {
@@ -213,9 +215,9 @@ public:
     return set_size (name, new_width, true);
   }
 
-  bool top_boxed_p () const override;
+  bool first_edge_has_border_p () const override;
 
-  bool bottom_boxed_p () const override;
+  bool last_edge_has_border_p () const override;
 
   void remove_windows (const char *name) override;