Enable eldoc-mode in existing clojure buffers

[pdbrown]

Fixes #2934

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[bbatsov]

I'm really puzzled by this part. In theory global-eldoc-mode should have trigged eldoc-mode, so it seems very weird to enable it manually if the global mode is enabled.

[pdbrown]

Yeah this does look very weird, so I just pushed an update to the inline comment. I looked into globalized minor modes a bit, and from what I can tell, they call their e.g. turn-on-eldoc-mode function when the global mode is toggled on or when new file-visiting buffers are created while it's on, and turn-on-eldoc-mode only actually enables eldoc-mode if eldoc--supported-p returns true when turn-on-eldoc-mode is called. So old clojure buffers did call turn-on-eldoc-mode, but it didn't do anything because eldoc wasn't supported before cider was enabled. Now that cider is enabled, eldoc is supported, but global minor modes won't re-run any turn-on functions in reponse to just enabling another minor mode (cider-mode), so we have to do it ourselves, but only if the user hasn't disabled global-eldoc-mode.

[bbatsov]

Okay, that makes sense. Thanks for looking into this!

[pdbrown]

No problem!