Document Setup.hs repl (#10481)

* Document `Setup.hs repl`

* fix whitespace

* delete out-dated instructions for sandbox

* Add full stops to the descriptions for options

doc/setup-commands.rst

@@ -1399,3 +1399,60 @@ This command takes the following option:
 
 
 .. include:: references.inc
+
+.. _setup-repl:
+
+runhaskell Setup.hs repl
+------------------------
+
+Open an interpreter session for the given component.
+
+Usage:
+
+.. program:: runhaskell Setup.hs repl [COMPONENT] [FLAGS]
+
+If the current directory contains no package, ignores COMPONENT parameters and
+opens an interactive interpreter session.
+
+Otherwise, (re)configures with the given or default flags, and loads the
+interpreter with the relevant modules. For executables, tests and benchmarks,
+loads the main module (and its dependencies); for libraries all exposed/other
+modules.
+
+The default component is the library itself, or the executable if that is the
+only component.
+
+Support for loading specific modules is planned but not implemented yet. For
+certain scenarios, ``Setup.hs exec -- ghci :l Foo`` may be used instead. Note
+that ``exec`` will not (re)configure and you will have to specify the location
+of other modules, if required.
+
+Flags for repl:
+
+.. option:: -v, --verbose[=n]
+
+    Control verbosity (n is 0--3, default verbosity level is 1).
+
+.. option:: --builddir=DIR
+
+    The directory where Cabal puts generated build files (default dist).
+
+.. option:: --with-PROG=PATH
+
+    Give the path to PROG.
+
+.. option:: --PROG-option=OPT
+
+    Give an extra option to PROG (no need to quote options containing spaces).
+
+.. option:: --PROG-options=OPTS
+
+    Give extra options to PROG.
+
+.. option:: --repl-no-load
+
+    Disable loading of project modules at REPL startup.
+
+.. option:: --repl-options=FLAG
+
+    Use the option(s) for the repl.