Cleanup: Use const context for some UI templates

- uiTemplateID: Straightforward, just const for the template
    and the functions it calls
  - uiTemplateCacheFile: Create a function in rna_ui.c because
    the generated RNA callback doesn't have const context.

Differential Revision: https://developer.blender.org/D7895

source/blender/editors/include/UI_interface.h

@@ -1938,7 +1938,7 @@ uiLayout *uiLayoutRadial(uiLayout *layout);
 /* templates */
 void uiTemplateHeader(uiLayout *layout, struct bContext *C);
 void uiTemplateID(uiLayout *layout,
-                  struct bContext *C,
+                  const struct bContext *C,
                   struct PointerRNA *ptr,
                   const char *propname,
                   const char *newop,
@@ -2111,7 +2111,7 @@ void uiTemplateComponentMenu(uiLayout *layout,
                              const char *name);
 void uiTemplateNodeSocket(uiLayout *layout, struct bContext *C, float *color);
 void uiTemplateCacheFile(uiLayout *layout,
-                         struct bContext *C,
+                         const struct bContext *C,
                          struct PointerRNA *ptr,
                          const char *propname);
 
@@ -2144,7 +2144,7 @@ void uiTemplateNodeView(uiLayout *layout,
                         struct bNodeSocket *input);
 void uiTemplateTextureUser(uiLayout *layout, struct bContext *C);
 void uiTemplateTextureShow(uiLayout *layout,
-                           struct bContext *C,
+                           const struct bContext *C,
                            struct PointerRNA *ptr,
                            struct PropertyRNA *prop);
 

source/blender/editors/interface/interface_templates.c

@@ -799,7 +799,7 @@ static uiBut *template_id_def_new_but(uiBlock *block,
   return but;
 }
 
-static void template_ID(bContext *C,
+static void template_ID(const bContext *C,
                         uiLayout *layout,
                         TemplateID *template_ui,
                         StructRNA *type,
@@ -1140,7 +1140,7 @@ ID *UI_context_active_but_get_tab_ID(bContext *C)
   }
 }
 
-static void template_ID_tabs(bContext *C,
+static void template_ID_tabs(const bContext *C,
                              uiLayout *layout,
                              TemplateID *template,
                              StructRNA *type,
@@ -1214,7 +1214,7 @@ static void template_ID_tabs(bContext *C,
 }
 
 static void ui_template_id(uiLayout *layout,
-                           bContext *C,
+                           const bContext *C,
                            PointerRNA *ptr,
                            const char *propname,
                            const char *newop,
@@ -1298,7 +1298,7 @@ static void ui_template_id(uiLayout *layout,
 }
 
 void uiTemplateID(uiLayout *layout,
-                  bContext *C,
+                  const bContext *C,
                   PointerRNA *ptr,
                   const char *propname,
                   const char *newop,
@@ -7523,7 +7523,10 @@ void uiTemplateNodeSocket(uiLayout *layout, bContext *UNUSED(C), float *color)
 /** \name Cache File Template
  * \{ */
 
-void uiTemplateCacheFile(uiLayout *layout, bContext *C, PointerRNA *ptr, const char *propname)
+void uiTemplateCacheFile(uiLayout *layout,
+                         const bContext *C,
+                         PointerRNA *ptr,
+                         const char *propname)
 {
   if (!ptr->data) {
     return;

source/blender/editors/space_buttons/buttons_texture.c

@@ -545,7 +545,7 @@ static void template_texture_show(bContext *C, void *data_p, void *prop_p)
   }
 }
 
-void uiTemplateTextureShow(uiLayout *layout, bContext *C, PointerRNA *ptr, PropertyRNA *prop)
+void uiTemplateTextureShow(uiLayout *layout, const bContext *C, PointerRNA *ptr, PropertyRNA *prop)
 {
   /* button to quickly show texture in texture tab */
   SpaceProperties *sbuts = CTX_wm_space_properties(C);

source/blender/makesrna/intern/rna_ui_api.c

@@ -485,6 +485,21 @@ static void rna_uiTemplateAnyID(uiLayout *layout,
   uiTemplateAnyID(layout, ptr, propname, proptypename, name);
 }
 
+static void rna_uiTemplateCacheFile(uiLayout *layout,
+                                    bContext *C,
+                                    PointerRNA *ptr,
+                                    const char *propname)
+{
+  PropertyRNA *prop = RNA_struct_find_property(ptr, propname);
+
+  if (!prop) {
+    RNA_warning("property not found: %s.%s", RNA_struct_identifier(ptr->type), propname);
+    return;
+  }
+
+  uiTemplateCacheFile(layout, C, ptr, propname);
+}
+
 static void rna_uiTemplatePathBuilder(uiLayout *layout,
                                       PointerRNA *ptr,
                                       const char *propname,
@@ -1577,7 +1592,7 @@ void RNA_api_ui_layout(StructRNA *srna)
   RNA_def_float_array(
       func, "color", 4, node_socket_color_default, 0.0f, 1.0f, "Color", "", 0.0f, 1.0f);
 
-  func = RNA_def_function(srna, "template_cache_file", "uiTemplateCacheFile");
+  func = RNA_def_function(srna, "template_cache_file", "rna_uiTemplateCacheFile");
   RNA_def_function_ui_description(
       func, "Item(s). User interface for selecting cache files and their source paths");
   RNA_def_function_flag(func, FUNC_USE_CONTEXT);