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Re: [PATCH] Caret diagnostics


On 10 April 2012 20:52, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
> On Tue, Apr 10, 2012 at 11:46 AM, Manuel LÃpez-IbÃÃez
> <lopezibanez@gmail.com> wrote:
>> On 10 April 2012 00:28, Jason Merrill <jason@redhat.com> wrote:
>>> On 04/09/2012 04:01 PM, Manuel LÃpez-IbÃÅez wrote:
>>>>
>>>> * It uses Âthe default cutoff as max_width, whatever it is (as
>>>> controlled by -fmessage-length).
>>>> * It uses the pretty-printer. The text cannot (should not) wrap
>>>> because we still print only max_width chars at most.
>>>
>>>
>>> Hmm, I think if pp_line_cutoff is 0 and we're on a terminal, we still want
>>> to use COLUMNS to limit how much of the source we print.
>>
>> Like this?
>
> There is a novelty in this new version that I don't think we discussed
> before: automatic expansion of tabs to 8 hard space characters. ÂThat
> number should not be hardcoded as there is no reason to believe a tab
> character always expands to 8 space characters. ÂYou should check
> the environment first; if not present the default expansion number should
> be a symbolic constant as opposed to a magic number sprinkled all over the
> places. ÂI would also encourage you to introduce more abstraction to
> reduce the size of diagnostic_show_locus.

There is no novelty, it has been there from the beginning, and now I
realize it was a mistake to do the extra work to implement this.

The GCS says: "Calculate column numbers assuming that space and all
ASCII printing characters have equal width, and assuming tab stops
every 8 columns"
http://www.gnu.org/prep/standards/standards.html#Errors

So, in fact, libcpp is buggy for not implementing this (as can be seen
in emacs). If/When libcpp is fixed, the column info will be correct
for tabs. And then, one may care about printing tabs as anything
different from a single space. But until then, a single space is a
good as anything. In fact this is what is done in c-ppoutput.c.

As can be seen below, this simplifies a lot the function, so I
appreciate the suggestion. If you have suggestions for removing other
code, I will be happy to implement them. The less code, the less
potential for bugs.

Cheers,

Manuel.

+/* Print the physical source line corresponding to the location of
+   this diagnostics, and a caret indicating the precise column.  */
+void
+diagnostic_show_locus (diagnostic_context * context,
+                      const diagnostic_info *diagnostic)
+{
+  const char *line;
+  char *buffer;
+  expanded_location s;
+  int real_width;
+  int max_width;
+  const char *saved_prefix;
+  int right_margin = 10;
+
+  if (!context->show_caret
+      || diagnostic->location <= BUILTINS_LOCATION)
+    return;
+
+  s = expand_location(diagnostic->location);
+  line = location_get_source_line (s);
+  if (line == NULL)
+    return;
+
+  real_width = strlen (line);
+
+  max_width = context->caret_max_width;
+  if (max_width <= 0)
+    max_width = INT_MAX;
+
+  /* If the line is longer than max_width and the column is too close
+     to max_width, skip part of the line until it is not so close.  */
+  right_margin = MIN(real_width - s.column, right_margin);
+  right_margin = max_width - right_margin;
+  if (real_width >= max_width && s.column > right_margin)
+    {
+      line += s.column - right_margin;
+      s.column = right_margin;
+    }
+
+  pp_newline (context->printer);
+  saved_prefix = pp_get_prefix (context->printer);
+  pp_set_prefix (context->printer, NULL);
+  pp_character (context->printer, ' ');
+  while (max_width > 0 && *line != '\0')
+    {
+      char c = *line == '\t' ? ' ' : *line;
+      pp_character (context->printer, c);
+      max_width--;
+      line++;
+    }
+  pp_newline (context->printer);
+  /* pp_printf does not implement %*c.  */
+  buffer = XALLOCAVEC (char, s.column + 3);
+  snprintf (buffer, s.column + 3, " %*c", s.column, '^');
+  pp_string (context->printer, buffer);
+  pp_set_prefix (context->printer, saved_prefix);
+}
+


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