[RFC] diagnostics.c: For terminals, restrict messages to terminal width?

2014-12-06  Tobias Burnus  <burnus@net-b.de>
	    Manuel López-Ibáñez  <manu@gcc.gnu.org>

gcc/
	* diagnostic.c (get_terminal_width): Renamed from getenv_columns,
	removed static, and additionally use ioctl to get width.
	(diagnostic_set_caret_max_width): Update call.
	* diagnostic.h (get_terminal_width): Add prototype.
	* opts.c (print_specific_help): Use it for x_help_columns.
	* doc/invoke.texi (fdiagnostics-show-caret): Document how the
	width is set.

gcc/fortran/
	* error.c (gfc_get_terminal_width): Renamed from
	get_terminal_width and use same-named common function.
	(gfc_error_init_1): Update call.

diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c
index 541e2fb..41101a2 100644
--- a/gcc/diagnostic.c
+++ b/gcc/diagnostic.c
@@ -33,6 +33,14 @@  along with GCC; see the file COPYING3.  If not see
 #include "diagnostic.h"
 #include "diagnostic-color.h"
 
+#ifdef HAVE_TERMIOS_H
+# include <termios.h>
+#endif
+
+#ifdef GWINSZ_IN_SYS_IOCTL
+# include <sys/ioctl.h>
+#endif
+
 #include <new>                     // For placement new.
 
 #define pedantic_warning_kind(DC)			\
@@ -81,9 +89,10 @@  file_name_as_prefix (diagnostic_context *context, const char *f)
 
 
 /* Return the value of the getenv("COLUMNS") as an integer. If the
-   value is not set to a positive integer, then return INT_MAX.  */
-static int
-getenv_columns (void)
+   value is not set to a positive integer, use ioctl to get the
+   terminal width. If it fails, return INT_MAX.  */
+int
+get_terminal_width (void)
 {
   const char * s = getenv ("COLUMNS");
   if (s != NULL) {
@@ -91,6 +100,14 @@  getenv_columns (void)
     if (n > 0)
       return n;
   }
+
+#ifdef TIOCGWINSZ
+  struct winsize w;
+  w.ws_col = 0;
+  if (ioctl (0, TIOCGWINSZ, &w) == 0 && w.ws_col > 0)
+    return w.ws_col;
+#endif
+
   return INT_MAX;
 }
 
@@ -101,7 +118,7 @@  diagnostic_set_caret_max_width (diagnostic_context *context, int value)
   /* One minus to account for the leading empty space.  */
   value = value ? value - 1 
     : (isatty (fileno (pp_buffer (context->printer)->stream))
-       ? getenv_columns () - 1: INT_MAX);
+       ? get_terminal_width () - 1: INT_MAX);
   
   if (value <= 0) 
     value = INT_MAX;
diff --git a/gcc/diagnostic.h b/gcc/diagnostic.h
index 807ce91..e699db8 100644
--- a/gcc/diagnostic.h
+++ b/gcc/diagnostic.h
@@ -298,6 +298,8 @@  void diagnostic_action_after_output (diagnostic_context *, diagnostic_t);
 
 void diagnostic_file_cache_fini (void);
 
+int get_terminal_width (void);
+
 /* Expand the location of this diagnostic. Use this function for consistency. */
 
 static inline expanded_location
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index d2f3c79..40eb8b6 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3187,7 +3187,10 @@  option is known to the diagnostic machinery).  Specifying the
 @opindex fdiagnostics-show-caret
 By default, each diagnostic emitted includes the original source line
 and a caret '^' indicating the column.  This option suppresses this
-information.
+information.  The source line is truncated to @var{n} characters, if
+the @option{-fmessage-length=n} is given.  When the output is done
+to the terminal, the width is limited to the width given by the
+@env{COLUMNS} environment variable or, if not set, to the terminal width.
 
 @end table
 
diff --git a/gcc/fortran/error.c b/gcc/fortran/error.c
index 541a799..75407dc 100644
--- a/gcc/fortran/error.c
+++ b/gcc/fortran/error.c
@@ -30,14 +30,6 @@  along with GCC; see the file COPYING3.  If not see
 #include "flags.h"
 #include "gfortran.h"
 
-#ifdef HAVE_TERMIOS_H
-# include <termios.h>
-#endif
-
-#ifdef GWINSZ_IN_SYS_IOCTL
-# include <sys/ioctl.h>
-#endif
-
 #include "diagnostic.h"
 #include "diagnostic-color.h"
 #include "tree-diagnostic.h" /* tree_diagnostics_defaults */
@@ -91,33 +83,9 @@  gfc_pop_suppress_errors (void)
 /* Determine terminal width (for trimming source lines in output).  */
 
 static int
-get_terminal_width (void)
+gfc_get_terminal_width (void)
 {
-  /* Only limit the width if we're outputting to a terminal.  */
-#ifdef HAVE_UNISTD_H
-  if (!isatty (STDERR_FILENO))
-    return INT_MAX;
-#endif
-  
-  /* Method #1: Use ioctl (not available on all systems).  */
-#ifdef TIOCGWINSZ
-  struct winsize w;
-  w.ws_col = 0;
-  if (ioctl (0, TIOCGWINSZ, &w) == 0 && w.ws_col > 0)
-    return w.ws_col;
-#endif
-
-  /* Method #2: Query environment variable $COLUMNS.  */
-  const char *p = getenv ("COLUMNS");
-  if (p)
-    {
-      int value = atoi (p);
-      if (value > 0)
-	return value;
-    }
-
-  /* If both fail, use reasonable default.  */
-  return 80;
+  return isatty (STDERR_FILENO) ? get_terminal_width () : INT_MAX;
 }
 
 
@@ -126,7 +94,7 @@  get_terminal_width (void)
 void
 gfc_error_init_1 (void)
 {
-  terminal_width = get_terminal_width ();
+  terminal_width = gfc_get_terminal_width ();
   errors = 0;
   warnings = 0;
   gfc_buffer_error (false);
diff --git a/gcc/opts.c b/gcc/opts.c
index 1b4f97e..34a42a5 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1231,18 +1231,8 @@  print_specific_help (unsigned int include_flags,
      the desired maximum width of the output.  */
   if (opts->x_help_columns == 0)
     {
-      const char *p;
-
-      p = getenv ("COLUMNS");
-      if (p != NULL)
-	{
-	  int value = atoi (p);
-
-	  if (value > 0)
-	    opts->x_help_columns = value;
-	}
-
-      if (opts->x_help_columns == 0)
+      opts->x_help_columns = get_terminal_width ();
+      if (opts->x_help_columns == INT_MAX)
 	/* Use a reasonable default.  */
 	opts->x_help_columns = 80;
     }