Make taxonomy_get_tree load entities by default

Problem/Motivation

The taxonomy module provides the taxonomy_get_tree() function that returns the terms' tree for a given vocabulary. It is used in the backend taxonomy administration page (admin/structure/taxonomy/[machine_name]), in the generation of Term reference field selectors (both in the backend create/edit forms and in the front-end, like for example Commerce add to cart forms) and is also used by plenty of contrib modules (taxonomy menu, views, etc...).

The problem with this function is that it directly calls the database to get the terms hierarchy, and then, only if the $load_entities parameter is set to TRUE, it loads each term's entity. This makes it impossible to use the hook_entity_load() hook when taxonomy_get_tree() is called, thus making modules relaying on it to alter the term entities on load not work properly. This is incoherent with the taxonomy_term_load_multiple(), that is used everywhere in the taxonomy module, and that always loads the term entities and even has its own hook (hook_taxonomy_term_load).

The most important module affected by this I've found is Title, which used together with Entity Translation has become the de-facto standard for proper content internationalization.

Proposed resolution

The proposed resolution is making the $load_entities parameter default to TRUE. This simple change makes all the taxonomy trees immediatelly work with any modules relying on the entity_load hook to alter term's properties (for instance, it shows them translated in the backend and in the term reference fields selector widget when using Title + ET). Yes, it adds a bit of overheat by loading each term's entity, but it's minimal because of the entity controller static cache and the taxonomy_get_tree() function's own cache and I think the alternatives to this are worse.

One alternative is to modify all the calls to taxonomy_get_tree() to set the $load_entities parameter to TRUE. This would have to be done everywhere it is called in core (including taxonomy, field, forum, node, etc... modules) and in all the contrib modules that want to use and/or render the term's name or any other field (99.99% I'd say). When you can just set the parameter to TRUE as default, that doesn't make a lot of sense. Similar to this, would be to "manually" use entity_load() at the same places.

The other alternative is to use hook_query_term_access_alter() to alter the query and modify the information you want. This seems like a really bad idea to me and would lead to conflicts between diferent modules altering the query.

Thinking if this change could break any existing code, I can't see how. Any code showing terms wants to allow for entity_load hooks to run so the behaviour is consistent everywhere. Any code not showing terms (for example using only the term IDs or weights) won't be affected, apart from the minimal overheat.

So basically, what I propose is changing:
function taxonomy_get_tree($vid, $parent = 0, $max_depth = NULL, $load_entities = FALSE) {
to:
function taxonomy_get_tree($vid, $parent = 0, $max_depth = NULL, $load_entities = TRUE) {
in core's taxonomy/taxonomy.module.

Just this simple modification would fix a fair amount of long-standing and complicated-to-solve-because-core-doesnt-care-about-i18n issues, for example:

• #2013985: Title replacement doesn't happen for taxonomy term references
• #2013849: Term names are not translated
• #1506054: Taxonomy term reference: language-aware widget and autocomplete (would help here)
• #1665308: [i18n] Integrate Taxonomy Menu with i18n_menu and entity_translation. (would help here)

Also, any module using taxonomy_get_tree() without setting the param to TRUE (very probable if you don't test in an internationalized installation) will automatically get support for Entity Translation + Title.