Introspection improvements (#3079)

* vala: Enhance the metadata to contain more symbols

* Enhance the introspection coverage

Always set data with destroy function as transfer full.

libvips/Vips-8.0.metadata

@@ -6,22 +6,32 @@ ClassMapFn.cls type="GLib.ObjectClass"
 ArgumentClassMapFn.object_class type="GLib.ObjectClass"
 ArgumentTable type="GLib.HashTable<GLib.ParamSpec,Vips.Argument?>"
 
-Image.eval#virtual_method skip
-Image.invalidate#virtual_method skip
-Image.minimise#virtual_method skip
-Image.posteval#virtual_method skip
-Image.preeval#virtual_method skip
-Image.written#virtual_method skip
-Image.memory skip
-Image.matrix_from_array skip
+ArrayDouble.newv skip=false
+ArrayImage.newv skip=false
+ArrayInt.newv skip=false
 
-Object.close#virtual_method skip
-Object.postbuild#virtual_method skip
-Object.postclose#virtual_method skip
-Object.preclose#virtual_method skip
+Image.*#method skip=false
+Image.eval#virtual_method name="eval_impl"
+Image.invalidate#virtual_method name="invalidate_impl"
+Image.minimise#virtual_method name="minimise_impl"
+Image.posteval#virtual_method name="posteval_impl"
+Image.preeval#virtual_method name="preeval_impl"
+Image.written#virtual_method name="written_impl"
+Image.written#virtual_method.result out
+Image.set_area.free_fn closure=-1 destroy=-1
+
+Object.close#virtual_method name="close_impl"
+Object.postbuild#virtual_method name="postbuild_impl"
+Object.postclose#virtual_method name="postclose_impl"
+Object.preclose#virtual_method name="preclose_impl"
 Object.preclose#method name="do_preclose"
+Object.sanity#virtual_method name="sanity_impl"
 _object_set_member name="set_member" parent="Vips.Object" symbol_type="method" instance_idx=0
 
+value_set_blob.free_fn closure=-1 destroy=-1
+value_set_area.free_fn closure=-1 destroy=-1
+Area.new.free_fn closure=-1 destroy=-1
+
 cache_* skip=false name="cache_(.+)" parent="Vips.Cache"
 col_* skip=false name="col_(.+)" parent="Vips.ColorUtils"
 tracked_* skip=false name="tracked_(.+)" parent="Vips.Tracked"

libvips/iofuncs/header.c

@@ -1545,8 +1545,8 @@ vips_image_get_fields( VipsImage *image )
  * vips_image_set_area:
  * @image: image to attach the metadata to
  * @name: metadata name
- * @free_fn: (scope async): free function for @data
- * @data: pointer to area of memory
+ * @free_fn: (scope async) (nullable): free function for @data
+ * @data: (transfer full): pointer to area of memory
  *
  * Attaches @data as a metadata item on @image under the name @name. When
  * VIPS no longer needs the metadata, it will be freed with @free_fn.
@@ -1622,8 +1622,9 @@ vips_image_get_area( const VipsImage *image,
  * vips_image_set_blob:
  * @image: image to attach the metadata to
  * @name: metadata name
- * @free_fn: (scope async): free function for @data
- * @data: (array length=length) (element-type guint8): pointer to area of memory
+ * @free_fn: (scope async) (nullable): free function for @data
+ * @data: (array length=length) (element-type guint8) (transfer full): pointer to area of
+ * memory
  * @length: length of memory area
  *
  * Attaches @blob as a metadata item on @image under the name @name. A 

libvips/iofuncs/type.c

@@ -238,8 +238,8 @@ vips_area_unref( VipsArea *area )
 
 /**
  * vips_area_new:
- * @free_fn: (scope async): @data will be freed with this function
- * @data: data will be freed with this function
+ * @free_fn: (scope async) (nullable): @data will be freed with this function
+ * @data: (transfer full): data will be freed with this function
  *
  * A VipsArea wraps a chunk of memory. It adds reference counting and a free
  * function. It also keeps a count and a %GType, so the area can be an array.
@@ -1511,8 +1511,8 @@ vips_array_image_get_type( void )
 /**
  * vips_value_set_area:
  * @value: set this value
- * @free_fn: (scope async): data will be freed with this function
- * @data: set @value to track this pointer
+ * @free_fn: (scope async) (nullable): data will be freed with this function
+ * @data: (transfer full): set @value to track this pointer
  *
  * Set value to be a ref-counted area of memory with a free function.
  */
@@ -1646,8 +1646,9 @@ vips_value_set_ref_string( GValue *value, const char *str )
 /** 
  * vips_value_set_blob:
  * @value: (out): GValue to set
- * @free_fn: (scope async): free function for @data
- * @data: pointer to area of memory
+ * @free_fn: (scope async) (nullable): free function for @data
+ * @data: (array length=length) (element-type guint8) (transfer full): pointer to area of
+ * memory
  * @length: length of memory area
  *
  * Sets @value to hold a @data. When @value is freed, @data will be
@@ -1676,7 +1677,8 @@ vips_value_set_blob( GValue *value,
 /** 
  * vips_value_set_blob_free:
  * @value: GValue to set
- * @data: pointer to area of memory
+ * @data: (transfer full) (array length=length) (element-type guint8) : pointer to area of
+ * memory
  * @length: length of memory area
  *
  * Just like vips_value_set_blob(), but when 
@@ -1712,7 +1714,8 @@ vips_value_set_blob_free( GValue *value, void *data, size_t length )
  *
  * See also: vips_value_set_blob()
  *
- * Returns: (transfer none): The pointer held by @value.
+ * Returns: (transfer none) (array length=length) (element-type guint8): The pointer held
+ * by @value.
  */
 void *
 vips_value_get_blob( const GValue *value, size_t *length )