* Add a script to retrieve licenses of the current derivation and of all its dependencies. To make it works, you need to change the default stdenv as documented in the error message.

./maintainers/scripts/dep-licenses.sh <attribute name>

svn path=/nixpkgs/trunk/; revision=18508

maintainers/scripts/dep-licenses.sh

···
+#!/bin/sh
+
+attr=$1
+
+: ${NIXPKGS=/etc/nixos/nixpkgs}
+
+tmp=$(mktemp --tmpdir -d nixpkgs-dep-license.XXXXXX)
+
+exitHandler() {
+    exitCode=$?
+    rm -rf "$tmp"
+    exit $exitCode
+}
+
+trap "exitHandler" EXIT
+
+# fetch the trace and the drvPath of the attribute.
+nix-instantiate $NIXPKGS -A $attr --show-trace > "$tmp/drvPath" 2> "$tmp/trace" || {
+  cat 1>&2 - "$tmp/trace" <<EOF
+An error occured while evaluating $attr.
+EOF
+  exit 1
+}
+
+# generate a sed script based on the trace output.
+sed '
+  \,@:.*:@, {
+    # \1  *.drv file
+    # \2  License terms
+    s,.*@:drv:\(.*\):\(.*\):@.*,s!\1!\1: \2!; t;,
+    s!Str(\\\"\([^,]*\)\\\",\[\])!\1!g
+    b
+  }
+  d
+' "$tmp/trace" > "$tmp/filter.sed"
+
+if test $(wc -l "$tmp/filter.sed" | sed 's/ .*//') == 0; then
+  echo 1>&2 "
+No derivation mentionned in the stack trace.  Either your derivation does
+not use stdenv.mkDerivation or you forgot to use the stdenv adapter named
+traceDrvLicenses.
+
+-  defaultStdenv = allStdenvs.stdenv;
++  defaultStdenv = traceDrvLicenses allStdenvs.stdenv;
+"
+  exit 1
+fi
+
+
+# remove all dependencies which are using stdenv.mkDerivation
+echo '
+d
+' >> "$tmp/filter.sed"
+
+nix-store -q --tree $(cat "$tmp/drvPath") | sed -f "$tmp/filter.sed"
+
+exit 0;

pkgs/stdenv/adapters.nix

···
           (stdenv.mkDerivation args)
           { meta.maintainers = maintainers; };
     };
+
+
+  /* Use the trace output to report all processed derivations with their
+     license name.
+ 
+  */
+  traceDrvLicenses = stdenv: stdenv //
+    { mkDerivation = args:
+        let
+          pkg = stdenv.mkDerivation args;
+          printDrvPath = val: let
+            drvPath = builtins.unsafeDiscardStringContext pkg.drvPath;
+            license =
+              if pkg ? meta && pkg.meta ? license then
+                pkg.meta.license
+              else
+                null;
+          in
+            builtins.trace "@:drv:${toString drvPath}:${builtins.exprToString license}:@"
+              val;
+        in pkg // {
+          outPath = printDrvPath pkg.outPath;
+          drvPath = printDrvPath pkg.drvPath;
+        };
+    };
 }