stdenv: add concatStringsSep helper

This can be used to separate lists for example with commas, when
creating argument strings. This works with both structuredAttrs disabled
and enabled.

pkgs/stdenv/generic/setup.sh

@@ -357,6 +357,36 @@ concatTo() {
     done
 }
 
+# Concatenate a list of strings ($2) with a separator ($1) between each element.
+# The list can be an indexed array of strings or a single string. A single string
+# is split on spaces and then concatenated with the separator.
+#
+# $ flags="lorem ipsum dolor sit amet"
+# $ concatStringsSep ";" flags
+# lorem;ipsum;dolor;sit;amet
+#
+# $ flags=("lorem ipsum" "dolor" "sit amet")
+# $ concatStringsSep ";" flags
+# lorem ipsum;dolor;sit amet
+concatStringsSep() {
+    local sep="$1"
+    local name="$2"
+    local type oldifs
+    if type=$(declare -p "$name" 2> /dev/null); then
+        local -n nameref="$name"
+        case "${type#* }" in
+            -A*)
+                echo "concatStringsSep(): ERROR: trying to use concatStringsSep on an associative array." >&2
+                return 1 ;;
+            -a*)
+                local IFS="$sep"
+                echo -n "${nameref[*]}" ;;
+            *)
+                echo -n "${nameref// /${sep}}" ;;
+        esac
+    fi
+}
+
 # Add $1/lib* into rpaths.
 # The function is used in multiple-outputs.sh hook,
 # so it is defined here but tried after the hook.

pkgs/test/stdenv/default.nix

@@ -131,6 +131,27 @@ let
         '';
       } // extraAttrs);
 
+  testConcatStringsSep = { name, stdenv' }:
+    stdenv'.mkDerivation
+      {
+        inherit name;
+
+        passAsFile = [ "buildCommand" ];
+        buildCommand = ''
+          declare -A associativeArray=(["X"]="Y")
+          [[ $(concatStringsSep ";" associativeArray 2>&1) =~ "trying to use" ]] || (echo "concatStringsSep did not throw concatenating associativeArray" && false)
+
+          string="lorem ipsum dolor sit amet"
+          stringWithSep="$(concatStringsSep ";" string)"
+          [[ "$stringWithSep" == "lorem;ipsum;dolor;sit;amet" ]] || (echo "'\$stringWithSep' was not 'lorem;ipsum;dolor;sit;amet'" && false)
+
+          array=("lorem ipsum" "dolor" "sit amet")
+          arrayWithSep="$(concatStringsSep ";" array)"
+          [[ "$arrayWithSep" == "lorem ipsum;dolor;sit amet" ]] || (echo "'\$arrayWithSep' was not 'lorem ipsum;dolor;sit amet'" && false)
+
+          touch $out
+        '';
+      };
 in
 
 {
@@ -236,6 +257,11 @@ in
     stdenv' = bootStdenv;
   };
 
+  test-concat-strings-sep = testConcatStringsSep {
+    name = "test-concat-strings-sep";
+    stdenv' = bootStdenv;
+  };
+
   test-structured-env-attrset = testEnvAttrset {
     name = "test-structured-env-attrset";
     stdenv' = bootStdenv;
@@ -313,6 +339,11 @@ in
       };
     };
 
+    test-concat-strings-sep = testConcatStringsSep {
+      name = "test-concat-strings-sep-structuredAttrsByDefault";
+      stdenv' = bootStdenvStructuredAttrsByDefault;
+    };
+
     test-golden-example-structuredAttrs =
       let
         goldenSh = earlyPkgs.writeText "goldenSh" ''