[gtk] GtkBuildableParser: Add a wrapper for GMarkupParser

[Matthias Clasen <matthiasc src gnome org>]

commit 135cea76fbe41cea7a83ebb3381bdc1410f8f9fb
Author: Alexander Larsson <alexl redhat com>
Date:   Mon Aug 26 23:28:18 2019 +0300

    GtkBuildableParser: Add a wrapper for GMarkupParser
    
    This currenly just wraps GMarkupParser, but the plan is to expose this
    instead of GMarkup in the GtkBuildable interfaces, allowing us to
    replace the parser with something that handles pre-parsed input
    instead.
    
    Note that we duplicate some of the features of GMarkup to implement
    the APIs rather then call down to GMarkup, as we need to support these
    in the pre-parsed case anyway.

 gtk/gtkbuildable.h      |  53 +++++++-
 gtk/gtkbuilderparser.c  | 319 ++++++++++++++++++++++++++++++++++++++++++++++++
 gtk/gtkbuilderprivate.h |  15 +++
 3 files changed, 386 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkbuildable.h b/gtk/gtkbuildable.h
index 6972abedd6..aec9c7b41a 100644
--- a/gtk/gtkbuildable.h
+++ b/gtk/gtkbuildable.h
@@ -33,10 +33,46 @@ G_BEGIN_DECLS
 #define GTK_IS_BUILDABLE(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GTK_TYPE_BUILDABLE))
 #define GTK_BUILDABLE_GET_IFACE(obj)  (G_TYPE_INSTANCE_GET_INTERFACE ((obj), GTK_TYPE_BUILDABLE, 
GtkBuildableIface))
 
-
 typedef struct _GtkBuildable      GtkBuildable; /* Dummy typedef */
 typedef struct _GtkBuildableIface GtkBuildableIface;
 
+typedef struct _GtkBuildableParseContext      GtkBuildableParseContext;
+typedef struct _GtkBuildableParser GtkBuildableParser;
+
+struct _GtkBuildableParser
+{
+  /* Called for open tags <foo bar="baz"> */
+  void (*start_element)  (GtkBuildableParseContext *context,
+                          const gchar              *element_name,
+                          const gchar             **attribute_names,
+                          const gchar             **attribute_values,
+                          gpointer                  user_data,
+                          GError                  **error);
+
+  /* Called for close tags </foo> */
+  void (*end_element)    (GtkBuildableParseContext *context,
+                          const gchar              *element_name,
+                          gpointer                  user_data,
+                          GError                  **error);
+
+  /* Called for character data */
+  /* text is not nul-terminated */
+  void (*text)           (GtkBuildableParseContext *context,
+                          const gchar              *text,
+                          gsize                     text_len,
+                          gpointer                  user_data,
+                          GError                  **error);
+
+  /* Called on error, including one set by other
+   * methods in the vtable. The GError should not be freed.
+   */
+  void (*error)          (GtkBuildableParseContext *context,
+                          GError                   *error,
+                          gpointer                 user_data);
+
+  gpointer padding[4];
+};
+
 /**
  * GtkBuildableIface:
  * @g_iface: the parent class
@@ -178,6 +214,21 @@ GObject * gtk_buildable_get_internal_child     (GtkBuildable        *buildable,
                                                GtkBuilder          *builder,
                                                const gchar         *childname);
 
+GDK_AVAILABLE_IN_ALL
+void          gtk_buildable_parse_context_push              (GtkBuildableParseContext *context,
+                                                             const GtkBuildableParser *parser,
+                                                             gpointer                  user_data);
+GDK_AVAILABLE_IN_ALL
+gpointer      gtk_buildable_parse_context_pop               (GtkBuildableParseContext *context);
+GDK_AVAILABLE_IN_ALL
+const char *  gtk_buildable_parse_context_get_element       (GtkBuildableParseContext *context);
+GDK_AVAILABLE_IN_ALL
+GPtrArray    *gtk_buildable_parse_context_get_element_stack (GtkBuildableParseContext *context);
+GDK_AVAILABLE_IN_ALL
+void          gtk_buildable_parse_context_get_position      (GtkBuildableParseContext *context,
+                                                             gint                *line_number,
+                                                             gint                *char_number);
+
 G_END_DECLS
 
 #endif /* __GTK_BUILDABLE_H__ */
diff --git a/gtk/gtkbuilderparser.c b/gtk/gtkbuilderparser.c
index 8a5a1608d6..d02e7192b3 100644
--- a/gtk/gtkbuilderparser.c
+++ b/gtk/gtkbuilderparser.c
@@ -31,6 +31,325 @@
 #include "gtkintl.h"
 
 
+typedef struct {
+  const GtkBuildableParser *last_parser;
+  gpointer last_user_data;
+  int last_depth;
+} GtkBuildableParserStack;
+
+static void
+pop_subparser_stack (GtkBuildableParseContext *context)
+{
+  GtkBuildableParserStack *stack =
+    &g_array_index (context->subparser_stack, GtkBuildableParserStack,
+                    context->subparser_stack->len - 1);
+
+  context->awaiting_pop = TRUE;
+  context->held_user_data = context->user_data;
+
+  context->user_data = stack->last_user_data;
+  context->parser = stack->last_parser;
+
+  g_array_set_size (context->subparser_stack, context->subparser_stack->len - 1);
+}
+
+static void
+possibly_finish_subparser (GtkBuildableParseContext *context)
+{
+  if (context->subparser_stack->len > 0)
+    {
+      GtkBuildableParserStack *stack =
+        &g_array_index (context->subparser_stack, GtkBuildableParserStack,
+                        context->subparser_stack->len - 1);
+
+      if (stack->last_depth ==  context->tag_stack->len)
+        pop_subparser_stack (context);
+    }
+}
+
+static void
+proxy_start_element (GMarkupParseContext *gm_context,
+                     const gchar         *element_name,
+                     const gchar        **attribute_names,
+                     const gchar        **attribute_values,
+                     gpointer             user_data,
+                     GError             **error)
+{
+  GtkBuildableParseContext *context = user_data;
+
+  // Due to the way GMarkup works we're sure this will live until the end_element callback
+  g_ptr_array_add (context->tag_stack, (char *)element_name);
+
+  if (context->parser->start_element)
+    context->parser->start_element (context, element_name,
+                                    attribute_names, attribute_values,
+                                    context->user_data, error);
+}
+
+static void
+proxy_end_element (GMarkupParseContext *gm_context,
+                   const gchar         *element_name,
+                   gpointer             user_data,
+                   GError             **error)
+{
+  GtkBuildableParseContext *context = user_data;
+
+  possibly_finish_subparser (context);
+
+  if (context->parser->end_element)
+    context->parser->end_element (context, element_name, context->user_data, error);
+
+  g_ptr_array_set_size (context->tag_stack, context->tag_stack->len - 1);
+}
+
+static void
+proxy_text (GMarkupParseContext *gm_context,
+            const gchar         *text,
+            gsize                text_len,
+            gpointer             user_data,
+            GError             **error)
+{
+  GtkBuildableParseContext *context = user_data;
+
+  if (context->parser->text)
+    context->parser->text (context, text, text_len,  context->user_data, error);
+}
+
+static void
+proxy_error (GMarkupParseContext *gm_context,
+             GError              *error,
+             gpointer             user_data)
+{
+  GtkBuildableParseContext *context = user_data;
+
+  if (context->parser->error)
+    context->parser->error (context, error, context->user_data);
+
+  /* report the error all the way up to free all the user-data */
+
+  while (context->subparser_stack->len > 0)
+    {
+      pop_subparser_stack (context);
+      context->awaiting_pop = FALSE; /* already been freed */
+
+      if (context->parser->error)
+        context->parser->error (context, error, context->user_data);
+    }
+}
+
+static const GMarkupParser gmarkup_parser = {
+  proxy_start_element,
+  proxy_end_element,
+  proxy_text,
+  NULL,
+  proxy_error,
+};
+
+static void
+gtk_buildable_parse_context_init (GtkBuildableParseContext *context,
+                                  const GtkBuildableParser *parser,
+                                  gpointer user_data)
+{
+  context->internal_callbacks = &gmarkup_parser;
+  context->ctx = NULL;
+
+  context->parser = parser;
+  context->user_data = user_data;
+
+  context->subparser_stack = g_array_new (FALSE, FALSE, sizeof (GtkBuildableParserStack));
+  context->tag_stack = g_ptr_array_new ();
+  context->held_user_data = NULL;
+  context->awaiting_pop = FALSE;
+}
+
+static void
+gtk_buildable_parse_context_free (GtkBuildableParseContext *context)
+{
+  g_array_unref (context->subparser_stack);
+  g_ptr_array_unref (context->tag_stack);
+}
+
+static gboolean
+gtk_buildable_parse_context_parse (GtkBuildableParseContext *context,
+                                   const gchar          *text,
+                                   gssize                text_len,
+                                   GError              **error)
+{
+  gboolean res;
+
+  context->ctx = g_markup_parse_context_new (context->internal_callbacks,
+                                             G_MARKUP_TREAT_CDATA_AS_TEXT,
+                                             context, NULL);
+  res = g_markup_parse_context_parse (context->ctx, text, text_len, error);
+  g_markup_parse_context_free  (context->ctx);
+
+  return res;
+}
+
+
+/**
+ * gtk_buildable_parse_context_push:
+ * @context: a #GtkBuildableParseContext
+ * @parser: a #GtkBuildableParser
+ * @user_data: user data to pass to #GtkBuildableParser functions
+ *
+ * Temporarily redirects markup data to a sub-parser.
+ *
+ * This function may only be called from the start_element handler of
+ * a #GtkBuildableParser. It must be matched with a corresponding call to
+ * gtk_buildable_parse_context_pop() in the matching end_element handler
+ * (except in the case that the parser aborts due to an error).
+ *
+ * All tags, text and other data between the matching tags is
+ * redirected to the subparser given by @parser. @user_data is used
+ * as the user_data for that parser. @user_data is also passed to the
+ * error callback in the event that an error occurs. This includes
+ * errors that occur in subparsers of the subparser.
+ *
+ * The end tag matching the start tag for which this call was made is
+ * handled by the previous parser (which is given its own user_data)
+ * which is why gtk_buildable_parse_context_pop() is provided to allow "one
+ * last access" to the @user_data provided to this function. In the
+ * case of error, the @user_data provided here is passed directly to
+ * the error callback of the subparser and gtk_buildable_parse_context_pop()
+ * should not be called. In either case, if @user_data was allocated
+ * then it ought to be freed from both of these locations.
+ *
+ * This function is not intended to be directly called by users
+ * interested in invoking subparsers. Instead, it is intended to be
+ * used by the subparsers themselves to implement a higher-level
+ * interface.
+ *
+ * For an example of how to use this, see g_markup_parse_context_push() which
+ * has the same kind of API.
+ **/
+void
+gtk_buildable_parse_context_push (GtkBuildableParseContext *context,
+                                  const GtkBuildableParser *parser,
+                                  gpointer                  user_data)
+{
+  GtkBuildableParserStack stack = { 0 };
+
+  stack.last_parser = context->parser;
+  stack.last_user_data = context->user_data;
+  stack.last_depth = context->tag_stack->len; // If at end_element time we're this deep, then pop it
+
+  context->parser = parser;
+  context->user_data = user_data;
+
+  g_array_append_val (context->subparser_stack, stack);
+}
+
+/**
+ * gtk_buildable_parse_context_pop:
+ * @context: a #GtkBuildableParseContext
+ *
+ * Completes the process of a temporary sub-parser redirection.
+ *
+ * This function exists to collect the user_data allocated by a
+ * matching call to gtk_buildable_parse_context_push(). It must be called
+ * in the end_element handler corresponding to the start_element
+ * handler during which gtk_buildable_parse_context_push() was called.
+ * You must not call this function from the error callback -- the
+ * @user_data is provided directly to the callback in that case.
+ *
+ * This function is not intended to be directly called by users
+ * interested in invoking subparsers. Instead, it is intended to
+ * be used by the subparsers themselves to implement a higher-level
+ * interface.
+ *
+ * Returns: the user data passed to gtk_buildable_parse_context_push()
+ */
+gpointer
+gtk_buildable_parse_context_pop (GtkBuildableParseContext *context)
+{
+  gpointer user_data;
+
+  if (!context->awaiting_pop)
+    possibly_finish_subparser (context);
+
+  g_assert (context->awaiting_pop);
+
+  context->awaiting_pop = FALSE;
+
+  user_data = context->held_user_data;
+  context->held_user_data = NULL;
+
+  return user_data;
+}
+
+/**
+ * gtk_buildable_parse_context_get_element:
+ * @context: a #GtkBuildablParseContext
+ *
+ * Retrieves the name of the currently open element.
+ *
+ * If called from the start_element or end_element handlers this will
+ * give the element_name as passed to those functions. For the parent
+ * elements, see gtk_buildable_parse_context_get_element_stack().
+ *
+ * Returns: the name of the currently open element, or %NULL
+ */
+const char *
+gtk_buildable_parse_context_get_element (GtkBuildableParseContext *context)
+{
+  if (context->tag_stack->len > 0)
+    return g_ptr_array_index (context->tag_stack, context->tag_stack->len - 1);
+  return NULL;
+}
+
+/**
+ * gtk_buildable_parse_context_get_element_stack:
+ * @context: a #GtkBuildableParseContext
+ *
+ * Retrieves the element stack from the internal state of the parser.
+ *
+ * The returned #GPtrArray is an array of strings where the last item is
+ * the currently open tag (as would be returned by
+ * gtk_buildable_parse_context_get_element()) and the previous item is its
+ * immediate parent.
+ *
+ * This function is intended to be used in the start_element and
+ * end_element handlers where gtk_buildable_parse_context_get_element()
+ * would merely return the name of the element that is being
+ * processed.
+ *
+ * Returns: the element stack, which must not be modified
+ */
+GPtrArray *
+gtk_buildable_parse_context_get_element_stack (GtkBuildableParseContext *context)
+{
+  return context->tag_stack;
+}
+
+/**
+ * gtk_buildable_parse_context_get_position:
+ * @context: a #GtkBuildableParseContext
+ * @line_number: (nullable): return location for a line number, or %NULL
+ * @char_number: (nullable): return location for a char-on-line number, or %NULL
+ *
+ * Retrieves the current line number and the number of the character on
+ * that line. Intended for use in error messages; there are no strict
+ * semantics for what constitutes the "current" line number other than
+ * "the best number we could come up with for error messages."
+ */
+void
+gtk_buildable_parse_context_get_position (GtkBuildableParseContext *context,
+                                          gint                *line_number,
+                                          gint                *char_number)
+
+{
+  if (context->ctx)
+    g_markup_parse_context_get_position (context->ctx, line_number, char_number);
+  else
+    {
+      if (line_number)
+        *line_number = 0;
+      if (char_number)
+        *char_number = 0;
+    }
+}
+
 static void free_property_info (PropertyInfo *info);
 static void free_object_info (ObjectInfo *info);
 
diff --git a/gtk/gtkbuilderprivate.h b/gtk/gtkbuilderprivate.h
index 29c2086ca4..d64616b639 100644
--- a/gtk/gtkbuilderprivate.h
+++ b/gtk/gtkbuilderprivate.h
@@ -20,6 +20,7 @@
 #define __GTK_BUILDER_PRIVATE_H__
 
 #include "gtkbuilder.h"
+#include "gtkbuildable.h"
 
 enum {
   TAG_PROPERTY,
@@ -99,6 +100,20 @@ typedef struct {
   gint     minor;
 } RequiresInfo;
 
+struct _GtkBuildableParseContext {
+  const GMarkupParser *internal_callbacks;
+  GMarkupParseContext *ctx;
+
+  const GtkBuildableParser *parser;
+  gpointer user_data;
+
+  GPtrArray *tag_stack;
+
+  GArray *subparser_stack;
+  gpointer held_user_data;
+  gboolean awaiting_pop;
+};
+
 typedef struct {
   GMarkupParser *parser;
   gchar *tagname;