Collect preprocessor definitions from the tags

This allows for more accurate highlighting of disabled sections as we
better know what is defined and what isn't.

This currently isn't perfect, because it doesn't take the value of the
define directive into account, nor honors undefs.

c-preproc-hl.c

@@ -22,6 +22,10 @@
 #include <geanyplugin.h>
 #include <SciLexer.h>
 
+/* FIXME: get this from Geany */
+#define TM_PARSER_C 0
+#define TM_PARSER_CPP 1
+
 
 #if 0
 static void rgb2hsl (const double r,
@@ -162,11 +166,14 @@ static sptr_t color_mul2 (const sptr_t c,
 #define ACTIVITY_FLAG 0x40 /* see LexCPP */
 
 
-static void setup_document (GeanyDocument *doc)
+static gboolean document_is_supported (GeanyDocument *doc)
 {
-  sptr_t lexer = scintilla_send_message (doc->editor->sci, SCI_GETLEXER, 0, 0);
+  return SCLEX_CPP == scintilla_send_message (doc->editor->sci, SCI_GETLEXER, 0, 0);
+}
 
-  if (lexer == SCLEX_CPP) {
+static void setup_document (GeanyDocument *doc)
+{
+  if (document_is_supported (doc)) {
     uptr_t i;
 
     scintilla_send_message (doc->editor->sci, SCI_SETPROPERTY,
@@ -212,11 +219,100 @@ static void on_filetype_set (GObject       *obj,
   setup_document (doc);
 }
 
+static gboolean lang_compatible (TMParserType a,
+                                 TMParserType b)
+{
+  /* mostly stolen from Geany */
+  return (a == b ||
+          (a == TM_PARSER_CPP && b == TM_PARSER_C) ||
+          (a == TM_PARSER_C && b == TM_PARSER_CPP));
+}
+
+/* try and determine whether @tag comes from a header or not.  @tag->local
+ * doesn't work because it's dummy in our implementation (see isIncludeFile()
+ * in CTags' source) */
+static gboolean tag_is_header (TMTag *tag)
+{
+  const gchar *ext;
+
+  if (tag->file && tag->file->short_name &&
+      (ext = strrchr (tag->file->short_name, '.'))) {
+    ++ext;
+
+    return ((ext[0] == 'h' /* optimize the match for .h* */ &&
+             (ext[1] == 0 /* h */ ||
+              ! g_ascii_strcasecmp (&ext[1], "h") /* hh */ ||
+              ! g_ascii_strcasecmp (&ext[1], "p") /* hp */ ||
+              ! g_ascii_strcasecmp (&ext[1], "pp") /* hpp */ ||
+              ! g_ascii_strcasecmp (&ext[1], "xx") /* hxx */ ||
+              ! g_ascii_strcasecmp (&ext[1], "++") /* h++ */)) ||
+            ! g_ascii_strcasecmp (ext, "tcc") /* from GCC's manual */);
+  } else {
+    return TRUE; /* global tag file (tag->file == NULL) or no extension */
+  }
+}
+
+static void collect_preprocessor_definitions_append (GPtrArray     *tags,
+                                                     GString       *str,
+                                                     TMParserType   lang,
+                                                     TMSourceFile  *current_file)
+{
+  if (tags) {
+    guint i;
+
+    for (i = 0; i < tags->len; i++) {
+      TMTag *tag = tags->pdata[i];
+
+      if (tag && lang_compatible (lang, tag->lang) &&
+          tag->type & (tm_tag_macro_t | tm_tag_macro_with_arg_t) &&
+          (! tag->file || tag->file != current_file) &&
+          tag_is_header (tag)) {
+        if (str->len > 0) {
+          g_string_append_c (str, ' ');
+        }
+        /* FIXME: we should find the value of the define somehow, so we catch
+         * 0s, and we should also catch undefs as such so we can drop it. */
+        g_string_append(str, tag->name);
+      }
+    }
+  }
+}
+
+static gchar *collect_preprocessor_definitions (const TMWorkspace  *ws,
+                                                TMParserType        lang,
+                                                TMSourceFile       *current_file)
+{
+  GString *str = g_string_new (NULL);
+
+  collect_preprocessor_definitions_append (ws->tags_array, str, lang, current_file);
+  collect_preprocessor_definitions_append (ws->global_tags, str, lang, current_file);
+
+  return g_string_free (str, FALSE);
+}
+
+static void on_document_activate (GObject        *obj,
+                                  GeanyDocument  *doc,
+                                  GeanyPlugin    *plugin)
+{
+  if (document_is_supported (doc)) {
+    gchar *words = collect_preprocessor_definitions (plugin->geany_data->app->tm_workspace,
+                                                     doc->file_type->lang,
+                                                     doc->tm_file);
+
+    if (words) {
+      scintilla_send_message (doc->editor->sci, SCI_SETKEYWORDS, 4, (sptr_t) words);
+      g_free (words);
+    }
+  }
+}
+
 static gboolean cph_init (GeanyPlugin  *plugin,
                           gpointer      data)
 {
   plugin_signal_connect (plugin, NULL, "document-filetype-set", TRUE,
                          G_CALLBACK (on_filetype_set), NULL);
+  plugin_signal_connect (plugin, NULL, "document-activate", TRUE,
+                         G_CALLBACK (on_document_activate), plugin);
 
   /* initial setup of currently open documents */
   if (main_is_realized ()) {