Apply a file to a templater `Open insert template modal` insertion, instead of using the current file

[garrett-is-a-swann]

Is your feature request related to a problem? Please describe.
For creating todos, I have a template like:

- [ ] <% tp.date.now("HH:mm") %> <% tp.file.cursor(1) %> (context:: <% tp.frontmatter.context %>) [[<% tp.file.title %>]] <% tp.file.cursor(0) %>      
	⌛<% tp.date.now("YYYY-MM-DD") %>	

This works great if I want to create todos within a file that the todo is about, but sometimes I want to create the todos in another file -- simplest example: a daily note.

Ideally there could be some way to apply a file context to a template that gets included into the current file.

Describe the solution you'd like
I'd like to apply a template with a file reference, that modifies some of the contexts for tp.file.title, tp.frontmatter.*, etc -- anything that relates to the current file should relate to the supplied file.

This could be via a secondary hotkey, similar to Open insert template modal, that called Templater: Open replace link template modal that replaces the obsidian [[note link]] under the cursor, and uses it as the file context as described above.

Describe alternatives you've considered
Another way to apply a link could be to have a secondary modal that accepts a link.

[garrett-is-a-swann]

Okay, I found a workaround... I can type a link, select the link, then run a template like:

<%*
let selection = tp.file.selection();
if (!selection) {
    return;
}
const target = {
    file: undefined,
    frontmatter: undefined
}

selection = selection
    .match(/\[\[([^|]*)\|?.*\]\]/)[1]
    ?.trim();
target.file = tp.file.find_tfile(selection);

if (!target.file) {
    return;
}
const file_cache = this.app.metadataCache.getFileCache(target.file);

target.frontmatter = file_cache?.frontmatter;
-%>
- [ ] <% tp.date.now("HH:mm") %> <% tp.file.cursor(1) %> (context:: <% target.frontmatter.context %>) [[<% target.file.basename %>]] <% tp.file.cursor(0) %>
	⌛<% tp.date.now("YYYY-MM-DD") %>	

This locates the file, and then applies the link. The only thing is, is I'm not sure how brittle this might be... Not sure if find_tfile might fail to find if there are duplicate names (Probably not, as the text should expand in links?), or if the target file might be missing from the cache for any reason making the frontmatter inaccessible...

If this is resilient enough, it can do for now, although it'd be nice for it to be a little simpler/more supported. While poking around, I also attempted to do:

tp.config.active_file = tp.file.find_tfile(selection);

in the javascript block, before using tp.frontmatter.context/tp.file.basename in the template body. This however, did not work -- although I could verify that those members were set correctly later, the active file was already cached. If that were supported, it'd be at least a little simpler, and possibly less prone to caching issues (if any exist).

[Zachatoo]

Not planning on supporting this, writing custom code as you did is the way forward here.