php: Add enabledExtensions attribute to PHP derivations

This provides a means to build a PHP package based on a list of
extensions from another.

For example, to generate a package with all default extensions
enabled, except opcache, but with ImageMagick:

php.withExtensions (e:
  (lib.filter (e: e != php.extensions.opcache) php.enabledExtensions)
  ++ [ e.imagick ])

2 files changed, 21 insertions, 6 deletions

diff --git a/doc/languages-frameworks/php.section.md b/doc/languages-frameworks/php.section.md
index cc98c760aec..a302a9a7f87 100644
--- a/doc/languages-frameworks/php.section.md
+++ b/doc/languages-frameworks/php.section.md
@@ -48,6 +48,21 @@ enabled:
 php.withExtensions (e: with e; [ imagick opcache ])
 ```
 
+Note that this will give you a package with _only_ opcache and
+ImageMagick, none of the other extensions which are enabled by default
+in the `php` package will be available.
+
+To enable building on a previous PHP package, the currently enabled
+extensions are made available in its `enabledExtensions`
+attribute. For example, to generate a package with all default
+extensions enabled, except opcache, but with ImageMagick:
+
+```nix
+php.withExtensions (e:
+  (lib.filter (e: e != php.extensions.opcache) php.enabledExtensions)
+  ++ [ e.imagick ])
+```
+
 If you want a PHP build with extra configuration in the `php.ini`
 file, you can use `php.buildEnv`. This function takes two named and
 optional parameters: `extensions` and `extraConfig`. `extensions`
diff --git a/pkgs/development/interpreters/php/default.nix b/pkgs/development/interpreters/php/default.nix
index e29f240ca55..d260a90e8ea 100644
--- a/pkgs/development/interpreters/php/default.nix
+++ b/pkgs/development/interpreters/php/default.nix
@@ -158,7 +158,7 @@ let
       buildEnv = { extensions ? (_: []), extraConfig ? "" }:
         let
           getExtName = ext: lib.removePrefix "php-" (builtins.parseDrvName ext.name).name;
-          extList = extensions php-packages.extensions;
+          enabledExtensions = extensions php-packages.extensions;
 
           # Generate extension load configuration snippets from the
           # extension parameter. This is an attrset suitable for use
@@ -178,9 +178,9 @@ let
                     deps = lib.optionals (ext ? internalDeps)
                       (map getExtName ext.internalDeps);
                   })
-                extList);
+                enabledExtensions);
 
-          extNames = map getExtName extList;
+          extNames = map getExtName enabledExtensions;
           extraInit = writeText "custom-php.ini" ''
             ${lib.concatStringsSep "\n"
               (lib.textClosureList extensionTexts extNames)}
@@ -189,11 +189,10 @@ let
         in
           symlinkJoin {
             name = "php-with-extensions-${version}";
-            inherit version;
-            inherit (php) dev;
+            inherit (php) version dev;
             nativeBuildInputs = [ makeWrapper ];
             passthru = {
-              inherit buildEnv withExtensions;
+              inherit buildEnv withExtensions enabledExtensions;
               inherit (php-packages) packages extensions;
             };
             paths = [ php ];
@@ -212,6 +211,7 @@ let
     in
       php.overrideAttrs (_: {
         passthru = {
+          enabledExtensions = [];
           inherit buildEnv withExtensions;
           inherit (php-packages) packages extensions;
         };