Support fix-it hints that add new lines

Previously fix-it hints couldn't contain newlines.  This is
due to the need to print something user-readable for them
within diagnostic-show-locus, and for handling them within
edit-context for printing diffs and regenerating content.

This patch enables limited support for fix-it hints with newlines,
for suggesting adding new lines.
Such a fix-it hint must have exactly one newline character, at the
end of the content.  It must be an insertion at the beginning of
a line (so that e.g. fix-its that split a pre-existing line are
still rejected).

They are printed by diagnostic-show-locus with a '+' in the
left-hand margin, like this:

test.c:42:4: note: suggest adding 'break;' here
+      break;
     case 'b':
     ^~~~~~~~~

and the printer injects "spans" if the insertion location is not
near the primary range of the diagnostic e.g.:

test.c:4:2: note: unrecognized 'putchar'; suggest including '<stdio.h>'
test.c:1:1:
+#include <stdio.h>

test.c:4:2:
  putchar (ch);
  ^~~~~~~

gcc/ChangeLog:
	* diagnostic-show-locus.c
	(layout::should_print_annotation_line_p): Make private.
	(layout::print_annotation_line): Make private.
	(layout::annotation_line_showed_range_p): Make private.
	(layout::show_ruler): Make private.
	(layout::print_source_line): Make private.  Pass in line and
	line_width, rather than calling location_get_source_line.  Drop
	returned value.
	(layout::print_leading_fixits): New method.
	(layout::print_any_fixits): Rename to...
	(layout::print_trailing_fixits): ...this, and make private.
	Don't print newline fixits.
	(diagnostic_show_locus): Move logic for printing one row into...
	(layout::print_line): ...this new function.  Move the
	location_get_source_line call and error-handling from
	print_source_line to here.  Call print_leading_fixits, and rename
	print_any_fixits to print_trailing_fixits.
	(selftest::test_fixit_insert_containing_newline): Update now that
	newlines are partially supported.
	(selftest::test_fixit_insert_containing_newline_2): New test.
	(selftest::test_fixit_replace_containing_newline): Update comments.
	(selftest::diagnostic_show_locus_c_tests): Call the new test.
	* edit-context.c (class added_line): New class.
	(class edited_line): Describe newline handling in comment.
	(edited_line::actually_edited_p): New method.
	(edited_line::print_content): Delete redundant decl.
	(edited_line::m_predecessors): New field.
	(edited_file::print_content): Call edited_line::print_content.
	(edited_file::print_diff): Update to support newlines.
	(edited_file::print_diff_hunk): Likewise.
	(edited_file::print_run_of_changed_lines): New function.
	(edited_file::print_diff_line): Convert to...
	(print_diff_line): ...this.
	(edited_file::get_effective_line_count): New function.
	(edited_line::edited_line): Initialize new field m_predecessors.
	(edited_line::~edited_line): Clean up m_predecessors.
	(edited_line::apply_fixit): Handle newlines.
	(edited_line::get_effective_line_count): New function.
	(edited_line::print_content): New function.
	(edited_line::print_diff_lines): New function.
	(selftest::test_applying_fixits_insert_containing_newline): New
	test.
	(selftest::test_applying_fixits_replace_containing_newline): New
	test.
	(selftest::insert_line): New function.
	(selftest::test_applying_fixits_multiple_lines): Add example of
	inserting a line.
	(selftest::edit_context_c_tests): Call the new tests.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic-test-show-locus-bw.c
	(test_fixit_insert_newline): New function.
	* gcc.dg/plugin/diagnostic-test-show-locus-color.c
	(test_fixit_insert_newline): New function.
	* gcc.dg/plugin/diagnostic-test-show-locus-generate-patch.c
	(test_fixit_insert_newline): New function.
	* gcc.dg/plugin/diagnostic-test-show-locus-parseable-fixits.c
	(test_fixit_insert_newline): New function.
	* gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
	(test_show_locus): Handle test_fixit_insert_newline.

libcpp/ChangeLog:
	* include/line-map.h (class rich_location): Update description of
	newline handling.
	(class fixit_hint): Likewise.
	(fixit_hint::ends_with_newline_p): New decl.
	* line-map.c (rich_location::maybe_add_fixit): Support newlines
	in fix-it hints that are insertions of single lines at the start
	of a line.  Don't consolidate into such fix-it hints.
	(fixit_hint::ends_with_newline_p): New method.

From-SVN: r247522

3 files changed, 69 insertions, 8 deletions

diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index ab225d5..c01ab44 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,14 @@
+2017-05-02  David Malcolm  <dmalcolm@redhat.com>
+
+	* include/line-map.h (class rich_location): Update description of
+	newline handling.
+	(class fixit_hint): Likewise.
+	(fixit_hint::ends_with_newline_p): New decl.
+	* line-map.c (rich_location::maybe_add_fixit): Support newlines
+	in fix-it hints that are insertions of single lines at the start
+	of a line.  Don't consolidate into such fix-it hints.
+	(fixit_hint::ends_with_newline_p): New method.
+
 2017-05-01  David Malcolm  <dmalcolm@redhat.com>
 
 	* include/line-map.h (source_range::intersects_line_p): Delete.
diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index 0c44f01..90d65d7 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -1551,7 +1551,11 @@ class fixit_hint;
 
    Attempts to add a fix-it hint within a macro expansion will fail.
 
-   We do not yet support newlines in fix-it text; attempts to do so will fail.
+   There is only limited support for newline characters in fix-it hints:
+   only hints with newlines which insert an entire new line are permitted,
+   inserting at the start of a line, and finishing with a newline
+   (with no interior newline characters).  Other attempts to add
+   fix-it hints containing newline characters will fail.
 
    The rich_location API handles these failures gracefully, so that
    diagnostics can attempt to add fix-it hints without each needing
@@ -1690,7 +1694,13 @@ protected:
        [start, next_loc)
    Insertions have start == next_loc: "replace" the empty string at the
    start location with the new string.
-   Deletions are replacement with the empty string.  */
+   Deletions are replacement with the empty string.
+
+   There is only limited support for newline characters in fix-it hints
+   as noted above in the comment for class rich_location.
+   A fixit_hint instance can have at most one newline character; if
+   present, the newline character must be the final character of
+   the content (preventing e.g. fix-its that split a pre-existing line).  */
 
 class fixit_hint
 {
@@ -1712,6 +1722,8 @@ class fixit_hint
 
   bool insertion_p () const { return m_start == m_next_loc; }
 
+  bool ends_with_newline_p () const;
+
  private:
   /* We don't use source_range here since, unlike most places,
      this is a half-open/half-closed range:
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index 176e58d..c4b7cb2 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -2325,16 +2325,44 @@ rich_location::maybe_add_fixit (source_location start,
   if (reject_impossible_fixit (next_loc))
     return;
 
-  /* We do not yet support newlines within fix-it hints.  */
-  if (strchr (new_content, '\n'))
+  const char *newline = strchr (new_content, '\n');
+  if (newline)
     {
-      stop_supporting_fixits ();
-      return;
+      /* For now, we can only support insertion of whole lines
+	 i.e. starts at start of line, and the newline is at the end of
+	 the insertion point.  */
+
+      /* It must be an insertion, not a replacement/deletion.  */
+      if (start != next_loc)
+	{
+	  stop_supporting_fixits ();
+	  return;
+	}
+
+      /* The insertion must be at the start of a line.  */
+      expanded_location exploc_start
+	= linemap_client_expand_location_to_spelling_point (start);
+      if (exploc_start.column != 1)
+	{
+	  stop_supporting_fixits ();
+	  return;
+	}
+
+      /* The newline must be at end of NEW_CONTENT.
+	 We could eventually split up fix-its at newlines if we wanted
+	 to allow more generality (e.g. to allow adding multiple lines
+	 with one add_fixit call.  */
+      if (newline[1] != '\0')
+	{
+	  stop_supporting_fixits ();
+	  return;
+	}
     }
 
-  /* Consolidate neighboring fixits.  */
+  /* Consolidate neighboring fixits.
+     Don't consolidate into newline-insertion fixits.  */
   fixit_hint *prev = get_last_fixit_hint ();
-  if (prev)
+  if (prev && !prev->ends_with_newline_p ())
     if (prev->maybe_append (start, next_loc, new_content))
       return;
 
@@ -2398,3 +2426,13 @@ fixit_hint::maybe_append (source_location start,
   m_bytes[m_len] = '\0';
   return true;
 }
+
+/* Return true iff this hint's content ends with a newline.  */
+
+bool
+fixit_hint::ends_with_newline_p () const
+{
+  if (m_len == 0)
+    return false;
+  return m_bytes[m_len - 1] == '\n';
+}