stdenv: support opt-in __structuredAttrs

Co-authored-by: Robin Gloster <mail@glob.in>

stdenv: print message if structuredAttrs is enabled

stdenv: add _append

reduces the chance of a user doing it wrong

fix nix develop issue

output hooks don't work yet in nix develop though

making $outputs be the same on non-structuredAttrs and structuredAttrs
is too much trouble.

lets instead make a function that gets the output names

reading environment file '/nix/store/2x7m69a2sm2kh0r6v0q5s9z1dh41m4xf-xz-5.2.5-env-bin'
nix: src/nix/develop.cc:299: std::string Common::makeRcScript(nix::ref<nix::Store>, const BuildEnvironment&, const Path&): Assertion `outputs != buildEnvironment.vars.end()' failed.

use a function to get all output names instead of using $outputs

copy env functionality from https://github.com/NixOS/nixpkgs/pull/76732/commits

1 files changed, 2 insertions, 2 deletions

diff --git a/pkgs/development/compilers/openjdk/19.nix b/pkgs/development/compilers/openjdk/19.nix
index 11b2fa60c73..9537b0d3ce5 100644
--- a/pkgs/development/compilers/openjdk/19.nix
+++ b/pkgs/development/compilers/openjdk/19.nix
@@ -140,12 +140,12 @@ let
     postFixup = ''
       # Build the set of output library directories to rpath against
       LIBDIRS=""
-      for output in $outputs; do
+      for output in $(getAllOutputNames); do
         if [ "$output" = debug ]; then continue; fi
         LIBDIRS="$(find $(eval echo \$$output) -name \*.so\* -exec dirname {} \+ | sort -u | tr '\n' ':'):$LIBDIRS"
       done
       # Add the local library paths to remove dependencies on the bootstrap
-      for output in $outputs; do
+      for output in $(getAllOutputNames); do
         if [ "$output" = debug ]; then continue; fi
         OUTPUTDIR=$(eval echo \$$output)
         BINLIBS=$(find $OUTPUTDIR/bin/ -type f; find $OUTPUTDIR -name \*.so\*)