Do not rely on $stdenv/setup to set output variables

Instead of relying on setup script to set output variables when
structured attributes are enabled, iterate over the values of an
outputs associative array.

See also
374fa3532e/pkgs/stdenv/generic/setup.sh (L23-L26)

src/nix/develop.cc

@@ -177,6 +177,14 @@ struct BuildEnvironment
             throw Error("bash variable is not a string");
     }
 
+    static Associative getAssociative(const Value & value)
+    {
+        if (auto assoc = std::get_if<Associative>(&value))
+            return *assoc;
+        else
+            throw Error("bash variable is not an associative array");
+    }
+
     static Array getStrings(const Value & value)
     {
         if (auto str = std::get_if<String>(&value))
@@ -362,14 +370,18 @@ struct Common : InstallableCommand, MixProfile
         auto outputs = buildEnvironment.vars.find("outputs");
         assert(outputs != buildEnvironment.vars.end());
 
-        // FIXME: properly unquote 'outputs'.
         StringMap rewrites;
+        if (buildEnvironment.providesStructuredAttrs()) {
+            for (auto & [outputName, from] : BuildEnvironment::getAssociative(outputs->second)) {
+                rewrites.insert({from, outputsDir + "/" + outputName});
+            }
+        } else {
             for (auto & outputName : BuildEnvironment::getStrings(outputs->second)) {
                 auto from = buildEnvironment.vars.find(outputName);
                 assert(from != buildEnvironment.vars.end());
-            // FIXME: unquote
                 rewrites.insert({BuildEnvironment::getString(from->second), outputsDir + "/" + outputName});
             }
+        }
 
         /* Substitute redirects. */
         for (auto & [installable_, dir_] : redirects) {

src/nix/get-env.sh

@@ -128,20 +128,25 @@ __escapeString() {
     printf '"%s"' "$__s"
 }
 
-# In case of `__structuredAttrs = true;` the list of outputs is an associative
-# array with a format like `outname => /nix/store/hash-drvname-outname`, so `__olist`
-# must contain the array's keys (hence `${!...[@]}`) in this case.
-if [ -e "$NIX_ATTRS_SH_FILE" ]; then
-    __olist="${!outputs[@]}"
-else
-    __olist=$outputs
-fi
-
-for __output in $__olist; do
-    if [[ -z $__done ]]; then
-        __dumpEnv > ${!__output}
+__dumpEnvToOutput() {
+    local __output="$1"
+    if [[ -z ${__done-} ]]; then
+        __dumpEnv > "$__output"
         __done=1
     else
-        echo -n >> "${!__output}"
+        echo -n >> "$__output"
     fi
+}
+
+# In case of `__structuredAttrs = true;` the list of outputs is an associative
+# array with a format like `outname => /nix/store/hash-drvname-outname`.
+# Otherwise it is a space-separated list of output variable names.
+if [ -e "$NIX_ATTRS_SH_FILE" ]; then
+    for __output in "${outputs[@]}"; do
+        __dumpEnvToOutput "$__output"
     done
+else
+    for __outname in $outputs; do
+        __dumpEnvToOutput "${!__outname}"
+    done
+fi

tests/functional/shell.nix

@@ -21,14 +21,6 @@ let pkgs = rec {
       export PATH=$PATH:$pkg/bin
     done
 
-    # mimic behavior of stdenv for `$out` etc. for structured attrs.
-    if [ -n "''${NIX_ATTRS_SH_FILE}" ]; then
-      for o in "''${!outputs[@]}"; do
-        eval "''${o}=''${outputs[$o]}"
-        export "''${o}"
-      done
-    fi
-
     declare -a arr1=(1 2 "3 4" 5)
     declare -a arr2=(x $'\n' $'x\ny')
     fun() {

tests/functional/structured-attrs.sh

@@ -32,4 +32,4 @@ jsonOut="$(nix print-dev-env -f structured-attrs-shell.nix --json)"
 
 test "$(<<<"$jsonOut" jq '.structuredAttrs|keys|.[]' -r)" = "$(printf ".attrs.json\n.attrs.sh")"
 
-test "$(<<<"$jsonOut" jq '.variables.out.value' -r)" = "$(<<<"$jsonOut" jq '.structuredAttrs.".attrs.json"' -r | jq -r '.outputs.out')"
+test "$(<<<"$jsonOut" jq '.variables.outputs.value.out' -r)" = "$(<<<"$jsonOut" jq '.structuredAttrs.".attrs.json"' -r | jq -r '.outputs.out')"