imp: less pager will use HLEDGER_LESS instead, if defined

When using `less` as pager, if HLEDGER_LESS is defined, it will
provide the options (instead of LESS + hledger's extra options).
You can set your own preferred options here, or you can set it
equal to LESS to use exactly those options.

[#2272]-related

hledger-lib/Hledger/Utils/IO.hs

@@ -213,6 +213,11 @@ getTerminalWidth  = fmap snd <$> getTerminalHeightWidth
 --   --use-backslash
 --   --use-color
 --
+-- You can choose different options by setting the HLEDGER_LESS variable;
+-- if set, its value will be used instead of LESS.
+-- Or you can force hledger to use your exact LESS settings,
+-- by setting HLEDGER_LESS equal to LESS.
+--
 setupPager :: IO ()
 setupPager = do
   let
@@ -231,11 +236,13 @@ setupPager = do
       ,"--use-backslash"
       ,"--use-color"
       ]
-  mless <- lookupEnv "LESS"
+  mhledgerless <- lookupEnv "HLEDGER_LESS"
+  mless        <- lookupEnv "LESS"
   setEnv "LESS" $
-    case mless of
+    case (mhledgerless, mless) of
-      Just less -> unwords [less, deflessopts]
+      (Just hledgerless, _) -> hledgerless
-      _         -> deflessopts
+      (_, Just less)        -> unwords [less, deflessopts]
+      _                     -> deflessopts
 
 -- | Display the given text on the terminal, trying to use a pager ($PAGER, less, or more)
 -- when appropriate, otherwise printing to standard output. Uses maybePagerFor.

hledger/hledger.m4.md

@@ -760,22 +760,34 @@ with a `y`/`yes` or `n`/`no` value to force it on or off.
 
 #### Paging
 
-In unix-like environments, when displaying large output in the terminal,
+In unix-like environments, when displaying large output (in any output format) in the terminal,
 hledger tries to use a pager when appropriate.
-(Actually it does this for any output format displayed in the terminal, not just text.)
-You can prevent this with the `--pager=no` option, perhaps in your config file.
-
-It will use the pager specified by the `PAGER` environment variable,
-otherwise `less` if available, otherwise `more` if available.
-
 The pager shows one page of text at a time, and lets you scroll around to see more.
-While it is active, usually `SPACE` shows the next page, `q` quits, and `?` shows more features.
+While it is active, usually `SPACE` shows the next page, `h` shows help, and `q` quits.
-(And in `less`, `G` jumps to the end, which is useful when you are viewing register output.)
+The home/end/page up/page down/cursor keys, and mouse scrolling, may also work.
 
+hledger will use the pager specified by the `PAGER` environment variable, otherwise `less` if available, otherwise `more` if available.
 The pager is expected to display hledger's ANSI colour and text styling.
-hledger adds `R` to the `LESS` and `MORE` environment variables to enable this for `less` and its `more` compatibility mode.
+(If you use a pager other than `less`, you might need to configure it to handle this.
-If you use a different pager, you might need to configure it similarly, to avoid seeing junk on screen.
+Or you could disable colour as described above.)
-(Or you can disable colour, as described above.)
+
+If you are using the `less` pager, hledger automatically appends a number of options to
+the `LESS` variable to enable ANSI colour and a number of other conveniences.
+(At the time of writing:
+--chop-long-lines
+--hilite-unread
+--ignore-case
+--mouse
+--no-init
+--quit-at-eof
+--quit-if-one-screen
+--RAW-CONTROL-CHARS
+--shift=8
+--squeeze-blank-lines
+--use-backslash
+--use-color
+).
+If these don't work well, you can set your preferred options in the `HLEDGER_LESS` variable, which will be used instead.
 
 ### HTML output
 
@@ -959,6 +971,10 @@ This is normally set by your terminal;
 some hledger commands (`register`) will format their output to this width.
 If not set, they will try to use the available terminal width.
 
+**HLEDGER_LESS**
+If `less` is your [pager](#paging), this variable specifies the `less` options hledger should use.
+(Otherwise, `LESS` + custom options are used.)
+
 **LEDGER_FILE**
 The main journal file to use when not specified with `-f/--file`.
 Default: `$HOME/.hledger.journal`.