Transaction folding

[drdv]

Even though ledger-occur can be used to narrow down a buffer based on a regex, I find it useful to have, in addiction, folding of transaction records. This PR implements the latter. For example, folding a transaction

2011/01/02 Grocery Store
    Expenses:Food:Groceries                  $ 65.00
    * Assets:Checking

results in

2011/01/02 Grocery Store...

Two interactive functions are exposed:

• ledger-mode-transaction-toggle-folding: hide/show transaction under point
• ledger-mode-folding-toggle-transactions: hide/show all transactions in the buffer

ledger-occur and transaction folding can be used to complement each other.

The buffer-local variable ledger-mode-toggle-invisible-transactions can be used to enable/disable folding of invisible transactions (i.e., transactions whose overlay has been set using ledger-occur).

Transaction blocks are detected using the same approach as in ledger-highlight-xact-under-point (probably some code refactoring should be done).

The transaction folding functionality has been added to the ledger-occur.el file even though probably a new file should be used (my aim was to do the least amount modifications). The same thing applies to the unit tests.

The function ledger-occur-make-invisible-overlay has been modified by adding (overlay-put ovl 'display "") in order to avoid undesired trailing ellipsis when using ledger-occur together with transaction folding.

Overlay of type 'code has been used in order for incremental search to temporarily open folded blocks.

[drdv]

Currently, the user might choose not to activate hs-minor-mode if he/she doesn't want to use the folding functionality. On the other hand, a warning is displayed when attempting to use the folding functionality without enabling hs-minor-mode.

[josephmturner]

I'm just stumbling across this now, and I like this idea. Is there a reason why this PR was not merged? Currently, I'm using the simpler folding technique described here:

; M-1 to collapse all transactions to one line, M-0 to reset. Useful for quickly scanning
(global-set-key "\M-0" (lambda () (interactive) (set-selective-display (* tab-width 0))))
(global-set-key "\M-1" (lambda () (interactive) (set-selective-display (* tab-width 1))))
(add-hook 'ledger-mode-hook (lambda () (setq tab-width 4)))

[drdv]

I don't know why it is not merged.

[jdek]

@drdv can you squash this into one commit? cc: @bcc32