Use char_span for return type of location_get_source_line

location_get_source_line returns a const char * that isn't 0-terminated,
writing back a length through an int * param.

This is error-prone, as all call-sites have to take into account the
lack of 0-termination, and respect the length of the buffer.

It's cleaner to bundle together this pointer+length state into a class,
so this patch does so, reusing the "char_span" class that I introduced
in r250187 (as part of the fix for PR c/81405).

The patch also adds assertions to all access to the char_span.

gcc/c-family/ChangeLog:
	* c-format.c (get_corrected_substring): Update for
	location_get_source_line returning a char_span.  Use a char_span
	when handling the prefix of the correction.
	* c-indentation.c (get_visual_column): Update for
	location_get_source_line returning a char_span.
	(get_first_nws_vis_column): Likewise.

gcc/ChangeLog:
	* diagnostic-show-locus.c (layout::layout): Update for
	location_get_source_line returning a char_span.
	(struct char_span): Move to input.h.
	(struct correction): Update for fields in char_span becoming
	private.
	(struct source_line): Update for location_get_source_line
	returning a char_span.
	(layout::print_line): Likewise.
	* edit-context.c (edited_file::print_content): Likewise.
	(edited_file::print_diff_hunk): Likewise.
	(edited_file::print_run_of_changed_lines): Likewise.
	(edited_file::get_num_lines): Likewise.
	(edited_line::edited_line): Likewise.
	* final.c (asm_show_source): Likewise.
	* input.c (location_get_source_line): Convert return type
	from const char * to char_span, losing the final "line_len"
	param.
	(dump_location_info): Update for the above.
	(get_substring_ranges_for_loc): Likewise.  Use a char_span
	when handling the literal within the line.
	(test_reading_source_line): Update for location_get_source_line
	returning a char_span.
	* input.h (class char_span): Move here from
	diagnostic-show-locus.c, converting from a struct to a class.
	Make data members private.
	(char_span::operator bool): New.
	(char_span::length): New.
	(char_span::get_buffer): New.
	(char_span::operator[]): New.
	(char_span::subspan): Make const.
	(char_span::xstrdup): New.
	(location_get_source_line): Convert return type from const char *
	to char_span, losing the final "line_size" param.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
	(test_show_locus): Update for location_get_source_line returning a
	char_span.  Use char_span for handling words in the
	"test_many_nested_locations" fix-it example.

From-SVN: r259768

3 files changed, 16 insertions, 12 deletions

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 27245b7e60d..ab85a73bd1b 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,12 @@
+2018-04-30  David Malcolm  <dmalcolm@redhat.com>
+
+	* c-format.c (get_corrected_substring): Update for
+	location_get_source_line returning a char_span.  Use a char_span
+	when handling the prefix of the correction.
+	* c-indentation.c (get_visual_column): Update for
+	location_get_source_line returning a char_span.
+	(get_first_nws_vis_column): Likewise.
+
 2018-03-29  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/84269
diff --git a/gcc/c-family/c-format.c b/gcc/c-family/c-format.c
index 3f4f83af219..ee7c33d97f2 100644
--- a/gcc/c-family/c-format.c
+++ b/gcc/c-family/c-format.c
@@ -3499,10 +3499,8 @@ get_corrected_substring (const substring_loc &fmt_loc,
   if (caret.column > finish.column)
     return NULL;
 
-  int line_width;
-  const char *line = location_get_source_line (start.file, start.line,
-					       &line_width);
-  if (line == NULL)
+  char_span line = location_get_source_line (start.file, start.line);
+  if (!line)
     return NULL;
 
   /* If we got this far, then we have the line containing the
@@ -3511,9 +3509,9 @@ get_corrected_substring (const substring_loc &fmt_loc,
      Generate a trimmed copy, containing the prefix part of the conversion
      specification, up to the (but not including) the length modifier.
      In the above example, this would be "%-+*.*".  */
-  const char *current_content = line + start.column - 1;
   int length_up_to_type = caret.column - start.column;
-  char *prefix = xstrndup (current_content, length_up_to_type);
+  char_span prefix_span = line.subspan (start.column - 1, length_up_to_type);
+  char *prefix = prefix_span.xstrdup ();
 
   /* Now attempt to generate a suggestion for the rest of the specification
      (length modifier and conversion char), based on ARG_TYPE and
diff --git a/gcc/c-family/c-indentation.c b/gcc/c-family/c-indentation.c
index acca44472e8..44b1e1e361f 100644
--- a/gcc/c-family/c-indentation.c
+++ b/gcc/c-family/c-indentation.c
@@ -70,9 +70,7 @@ get_visual_column (expanded_location exploc, location_t loc,
       return false;
     }
 
-  int line_len;
-  const char *line = location_get_source_line (exploc.file, exploc.line,
-					       &line_len);
+  char_span line = location_get_source_line (exploc.file, exploc.line);
   if (!line)
     return false;
   unsigned int vis_column = 0;
@@ -112,12 +110,11 @@ get_first_nws_vis_column (const char *file, int line_num,
 {
   gcc_assert (first_nws);
 
-  int line_len;
-  const char *line = location_get_source_line (file, line_num, &line_len);
+  char_span line = location_get_source_line (file, line_num);
   if (!line)
     return false;
   unsigned int vis_column = 0;
-  for (int i = 1; i < line_len; i++)
+  for (size_t i = 1; i < line.length (); i++)
     {
       unsigned char ch = line[i - 1];