Do not emit style escape sequences to log file

PR gdb/24502 requests that the "set logging" log file not contain
style escape sequences emitted by gdb.

This seemed like a reasonable request to me, so this patch implements
filtering for the log file.

This also updates a comment in ui-style.h that I noticed while writing
the patch.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-06-14  Tom Tromey  <tromey@adacore.com>

	PR gdb/24502:
	* ui-style.h (skip_ansi_escape): Update comment.
	* ui-file.h (class no_terminal_escape_file): New class.
	* ui-file.c (no_terminal_escape_file::write)
	(no_terminal_escape_file::puts): New methods.
	* cli/cli-logging.c (handle_redirections): Use
	no_terminal_escape_file.

gdb/testsuite/ChangeLog
2019-06-14  Tom Tromey  <tromey@adacore.com>

	PR gdb/24502:
	* gdb.base/style-logging.exp: New file.

1 files changed, 32 insertions, 0 deletions

diff --git a/gdb/ui-file.c b/gdb/ui-file.c
index 24c914f..05d411a 100644
--- a/gdb/ui-file.c
+++ b/gdb/ui-file.c
@@ -396,3 +396,35 @@ tee_file::can_emit_style_escape ()
 	  && m_one->term_out ()
 	  && term_cli_styling ());
 }
+
+/* See ui-file.h.  */
+
+void
+no_terminal_escape_file::write (const char *buf, long length_buf)
+{
+  std::string copy (buf, length_buf);
+  this->puts (copy.c_str ());
+}
+
+/* See ui-file.h.  */
+
+void
+no_terminal_escape_file::puts (const char *buf)
+{
+  while (*buf != '\0')
+    {
+      const char *esc = strchr (buf, '\033');
+      if (esc == nullptr)
+	break;
+
+      int n_read = 0;
+      if (!skip_ansi_escape (esc, &n_read))
+	++esc;
+
+      this->stdio_file::write (buf, esc - buf);
+      buf = esc + n_read;
+    }
+
+  if (*buf != '\0')
+    this->stdio_file::write (buf, strlen (buf));
+}