From 92ff1d3be43f725121764ecc67d1fd992e15d7ce Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Fri, 14 Jun 2024 16:58:57 -0500
Subject: [PATCH] Add `only` option to `merge-module` and `import`.

This allows importing only selected bindings.

For example,

    (import foo :only [bar baz])

    (foo/bar) # works
    (foo/buzz) # doesn't work, even if the foo module has a buzz
    function.
---
 CHANGELOG.md        |  1 +
 src/boot/boot.janet | 12 +++++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 10987dda..6a7597ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Add `:only` argument to `import` to allow for easier control over imported bindings.
 - Add extra optional `env` argument to `eval` and `eval-string`.
 - Allow naming function literals with a keyword. This allows better stacktraces for macros without
   accidentally adding new bindings.
diff --git a/src/boot/boot.janet b/src/boot/boot.janet
index dd793013..9878e669 100644
--- a/src/boot/boot.janet
+++ b/src/boot/boot.janet
@@ -3040,9 +3040,10 @@
   ``Merge a module source into the `target` environment with a `prefix`, as with the `import` macro.
   This lets users emulate the behavior of `import` with a custom module table.
   If `export` is truthy, then merged functions are not marked as private. Returns
-  the modified target environment.``
-  [target source &opt prefix export]
-  (loop [[k v] :pairs source :when (symbol? k) :when (not (v :private))]
+  the modified target environment. If an array `only` is passed, only merge keys in `only`.``
+  [target source &opt prefix export only]
+  (def only-set (if only (invert only)))
+  (loop [[k v] :pairs source :when (symbol? k) :when (not (v :private)) :when (or (not only) (in only-set k))]
     (def newv (table/setproto @{:private (not export)} v))
     (put target (symbol prefix k) newv))
   target)
@@ -3055,13 +3056,14 @@
   (def kargs (table ;args))
   (def {:as as
         :prefix prefix
-        :export ep} kargs)
+        :export ep
+        :only only} kargs)
   (def newenv (require-1 path args kargs))
   (def prefix (or
                 (and as (string as "/"))
                 prefix
                 (string (last (string/split "/" path)) "/")))
-  (merge-module env newenv prefix ep))
+  (merge-module env newenv prefix ep only))
 
 (defmacro import
   ``Import a module. First requires the module, and then merges its