From 8d3355724ff90a1660acf591e4aa35c82c913b38 Mon Sep 17 00:00:00 2001
From: David Malcolm <dmalcolm@redhat.com>
Date: Mon, 5 Jun 2017 13:29:31 -0400
Subject: [PATCH 3/6] libcpp: add callback for comment-handling

Currently the C/C++ frontends discard comments when parsing.
It's possible to set up libcpp to capture comments as tokens,
by setting CPP_OPTION (pfile, discard_comments) to false),
and this can be enabled using the -C command line option (see
also -CC), but c-family/c-lex.c then discards any CPP_COMMENT
tokens it sees, so they're not seen by the frontend parser.

The following patch adds an (optional) callback to libcpp
for handling comments, giving the comment content, and the
location it was seen at.  This approach allows arbitrary
logic to be wired up to comments, and avoids having to
copy the comment content to a new buffer (which the CPP_COMMENT
approach does).

This could be used by plugins to chain up on the callback
e.g. to parse specially-formatted comments, e.g. for
documentation generation, or e.g. for GObject introspection
annotations [1].

Test coverage is via a C++ plugin (so that we can test both C and C++
style comments, without needing a dg-options directive).

[1] https://wiki.gnome.org/Projects/GObjectIntrospection/Annotations

gcc/testsuite/ChangeLog:
	* g++.dg/plugin/comment_plugin.c: New test plugin.
	* g++.dg/plugin/comments-1.C: New test file.
	* g++.dg/plugin/plugin.exp (plugin_test_list): Add the above.

libcpp/ChangeLog:
	* include/cpplib.h (struct cpp_callbacks): Add "comment"
	callback.
	* lex.c (_cpp_lex_direct): Call the comment callback if non-NULL.
---
 gcc/testsuite/g++.dg/plugin/comment_plugin.c | 63 ++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/plugin/comments-1.C     | 49 ++++++++++++++++++++++
 gcc/testsuite/g++.dg/plugin/plugin.exp       |  1 +
 libcpp/include/cpplib.h                      |  9 ++++
 libcpp/lex.c                                 |  7 ++++
 5 files changed, 129 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/plugin/comment_plugin.c
 create mode 100644 gcc/testsuite/g++.dg/plugin/comments-1.C

diff --git a/gcc/testsuite/g++.dg/plugin/comment_plugin.c b/gcc/testsuite/g++.dg/plugin/comment_plugin.c
new file mode 100644
index 0000000..c3b08e3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/plugin/comment_plugin.c
@@ -0,0 +1,63 @@
+/* Test of cpp_callbacks::comments.  */
+
+#include "gcc-plugin.h"
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "cpplib.h"
+#include "diagnostic.h"
+#include "c-family/c-pragma.h"
+
+int plugin_is_GPL_compatible;
+
+/* Test callback for cpp_callbacks::comments.  */
+
+void
+my_comment_cb (cpp_reader *, source_location loc,
+	       const unsigned char *content, size_t len)
+{
+  if (in_system_header_at (loc))
+    return;
+
+  /* CONTENT contains the opening slash-star (or slash-slash),
+     and for C-style comments contains the closing star-slash.  */
+  gcc_assert (len >= 2);
+  gcc_assert (content[0] == '/');
+  gcc_assert (content[1] == '*' || content[1] == '/');
+  bool c_style = (content[1] == '*');
+  if (c_style)
+    {
+      gcc_assert (content[len - 2] == '*');
+      gcc_assert (content[len - 1] == '/');
+    }
+
+  if (c_style)
+    inform (loc, "got C-style comment; length=%i", len);
+  else
+    inform (loc, "got C++-style comment; length=%i", len);
+
+  /* Print the content of the comment.
+     For a C-style comment, the buffer CONTENT contains the opening
+     slash-star and closing star-slash, so we can't directly verify
+     it in the DejaGnu test without adding another comment, which
+     would trigger this callback again.
+     Hence we skip the syntactically-significant parts of the comment
+     when printing it.  */
+  fprintf (stderr, "stripped content of comment: >");
+  /* Avoid printing trailing star-slash.  */
+  if (c_style)
+    len -= 2;
+  for (size_t i = 2; i < len; i++)
+    fputc (content[i], stderr);
+  fprintf (stderr, "<\n");
+}
+
+int
+plugin_init (struct plugin_name_args *plugin_info,
+	     struct plugin_gcc_version *version)
+{
+  cpp_callbacks *cb = cpp_get_callbacks (parse_in);
+  cb->comment = my_comment_cb;
+
+  return 0;
+}
diff --git a/gcc/testsuite/g++.dg/plugin/comments-1.C b/gcc/testsuite/g++.dg/plugin/comments-1.C
new file mode 100644
index 0000000..0821b14
--- /dev/null
+++ b/gcc/testsuite/g++.dg/plugin/comments-1.C
@@ -0,0 +1,49 @@
+/* Example of a one-line C-style comment.  */
+#if 0
+{ dg-message "1: got C-style comment; length=45" "" { target *-*-* } .-2 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: > Example of a one-line C-style comment.  <
+{ dg-end-multiline-output "" }
+#endif
+
+     /*Another example of a one-line C-style comment.*/
+#if 0
+{ dg-message "6: got C-style comment; length=50" "" { target *-*-* } .-2 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: >Another example of a one-line C-style comment.<
+{ dg-end-multiline-output "" }
+#endif
+
+/**/
+#if 0
+{ dg-message "1: got C-style comment; length=4" "" { target *-*-* } .-2 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: ><
+{ dg-end-multiline-output "" }
+#endif
+
+/* Example of a
+   multi-line C-style comment.  */
+#if 0
+{ dg-message "1: got C-style comment; length=50" "" { target *-*-* } .-3 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: > Example of a
+   multi-line C-style comment.  <
+{ dg-end-multiline-output "" }
+#endif
+
+// Example of a C++-style comment
+#if 0
+{ dg-message "1: got C\\+\\+-style comment; length=33" "" { target *-*-* } .-2 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: > Example of a C++-style comment<
+{ dg-end-multiline-output "" }
+#endif
+
+//
+#if 0
+{ dg-message "1: got C\\+\\+-style comment; length=2" "" { target *-*-* } .-2 }
+{ dg-begin-multiline-output "" }
+stripped content of comment: ><
+{ dg-end-multiline-output "" }
+#endif
diff --git a/gcc/testsuite/g++.dg/plugin/plugin.exp b/gcc/testsuite/g++.dg/plugin/plugin.exp
index 94ebe93..e40cba3 100644
--- a/gcc/testsuite/g++.dg/plugin/plugin.exp
+++ b/gcc/testsuite/g++.dg/plugin/plugin.exp
@@ -68,6 +68,7 @@ set plugin_test_list [list \
     { show_template_tree_color_plugin.c \
     	  show-template-tree-color.C \
     	  show-template-tree-color-no-elide-type.C } \
+    { comment_plugin.c comments-1.C } \
 ]
 
 foreach plugin_test $plugin_test_list {
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index b843992..66ef4d6 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -609,6 +609,15 @@ struct cpp_callbacks
 
   /* Callback for providing suggestions for misspelled directives.  */
   const char *(*get_suggestion) (cpp_reader *, const char *, const char *const *);
+
+  /* Callback for when a comment is encountered, giving the location
+     of the opening slash, a pointer to the content (which is not
+     necessarily 0-terminated), and the length of the content.
+     The content contains the opening slash-star (or slash-slash),
+     and for C-style comments contains the closing star-slash.  For
+     C++-style comments it does not include the terminating newline.  */
+  void (*comment) (cpp_reader *, source_location, const unsigned char *,
+		   size_t);
 };
 
 #ifdef VMS
diff --git a/libcpp/lex.c b/libcpp/lex.c
index 9edd2a6..40ff801 100644
--- a/libcpp/lex.c
+++ b/libcpp/lex.c
@@ -2889,6 +2889,13 @@ _cpp_lex_direct (cpp_reader *pfile)
       if (fallthrough_comment_p (pfile, comment_start))
 	fallthrough_comment = true;
 
+      if (pfile->cb.comment)
+	{
+	  size_t len = pfile->buffer->cur - comment_start;
+	  pfile->cb.comment (pfile, result->src_loc, comment_start - 1,
+			     len + 1);
+	}
+
       if (!pfile->state.save_comments)
 	{
 	  result->flags |= PREV_WHITE;
-- 
1.8.5.3