[PATCH v3 11/21] Restore ui_file::can_page

[Tom Tromey <tom@tromey.com>]

A while back, I removed the ui_file::can_page method.  It wasn't
needed for a while, due to how output redirections were done.

With the new approach in this series, it's convenient to have this
method again, because the pipeline downstream from the pager won't
change when logging -- the logging filter will be enabled or disabled
without reconfiguring the pipeline.  This method lets the pager adapt
correctly.
---
 gdb/ui-file.h | 18 ++++++++++++++++++
 gdb/utils.c   |  6 ++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/gdb/ui-file.h b/gdb/ui-file.h
index 231c32deafc..4aaf4d0e54e 100644
--- a/gdb/ui-file.h
+++ b/gdb/ui-file.h
@@ -101,6 +101,14 @@ class ui_file
   virtual int fd () const
   { return -1; }
 
+  /* Return true if this object supports paging, false otherwise.  */
+  virtual bool can_page () const
+  {
+    /* Almost no file supports paging, which is why this is the
+       default.  */
+    return false;
+  }
+
   /* Indicate that if the next sequence of characters overflows the
      line, a newline should be inserted here rather than when it hits
      the end.  If INDENT is non-zero, it is a number of spaces to be
@@ -270,6 +278,11 @@ class stdio_file : public ui_file
   int fd () const override
   { return m_fd; }
 
+  bool can_page () const override
+  {
+    return m_file == stdout;
+  }
+
 private:
   /* Sets the internal stream to FILE, and saves the FILE's file
      descriptor in M_FD.  */
@@ -452,6 +465,11 @@ class wrapped_file : public ui_file
   void write_async_safe (const char *buf, long length_buf) override
   { return m_stream->write_async_safe (buf, length_buf); }
 
+  bool can_page () const override
+  {
+    return m_stream->can_page ();
+  }
+
 protected:
 
   explicit wrapped_file (T stream)
diff --git a/gdb/utils.c b/gdb/utils.c
index f4c9e584628..03a1d9146f2 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -1640,7 +1640,8 @@ pager_file::check_for_overfull_line (const unsigned int lines_allowed)
 	 this loop, so we must continue to check it here.  */
       if (pagination_enabled
 	  && !pagination_disabled_for_command
-	  && lines_printed >= lines_allowed)
+	  && lines_printed >= lines_allowed
+	  && m_stream->can_page ())
 	{
 	  prompt_for_continue ();
 	  did_paginate = true;
@@ -1713,7 +1714,8 @@ pager_file::puts (const char *linebuffer)
 	 it here.  */
       if (pagination_enabled
 	  && !pagination_disabled_for_command
-	  && lines_printed >= lines_allowed)
+	  && lines_printed >= lines_allowed
+	  && m_stream->can_page ())
 	prompt_for_continue ();
 
       while (*linebuffer != '\0' && *linebuffer != '\n')

-- 
2.49.0