split build phase

Parts of the old buildPhase actually belong in unpack or configure.

esp32-tools.nix

-{ lib, stdenv, fetchurl, fetchgit, fetchFromGitHub, espressif-crosstool-ng, autoconf, automake, bison, flex, unzip, help2man, libtool, which, texinfo, file, wget, gnum4, perl, ncurses, python3 }:
+{ lib, stdenv, fetchurl, fetchgit, fetchFromGitHub, espressif-crosstool-ng, autoconf, automake, bison, flex, unzip, help2man, libtool,
+  which, texinfo, file, wget, gnum4, perl, ncurses, python3 }:
 let
   srcs = import ./sources.nix { inherit fetchFromGitHub; };
   srcs2 = import ./sources2.nix { inherit fetchurl fetchgit fetchFromGitHub; };
 in stdenv.mkDerivation {
   pname = "espressif-esp32-tools";
-  inherit (srcs) version srcs unpackPhase;
+  inherit (srcs) version srcs;
 
   additionalSources = lib.strings.concatStringsSep "\n"
     (lib.attrsets.mapAttrsToList (name: drv: if drv ? outPath then "${name} ${drv.outPath}" else "") srcs2);
@@ -14,14 +15,7 @@ in stdenv.mkDerivation {
 
   hardeningDisable = [ "format" "pie" ];
 
-  dontConfigure = true;
-
-  buildPhase = ''
-    unset CC CXX
-    ct-ng xtensa-esp32-elf
-
-    echo "CT_LOCAL_TARBALLS_DIR=$PWD/tarballs" >>.config
-    echo "CT_FORBID_DOWNLOAD=y" >>.config
+  unpackPhase = srcs.unpackPhase + ''
     mkdir tarballs
     while read name path ; do
       printf "%-30s -> %s\\n" $name $path
@@ -34,12 +28,19 @@ in stdenv.mkDerivation {
         ln -s $path tarballs/$name
       fi
     done <<<"$additionalSources"
+  '';
 
-    # for debugging, see `ct-ng list-steps`
-    #export CT_DEBUG_CT_SAVE_STEPS=y
+  configurePhase = ''
+    unset CC CXX
+    ct-ng xtensa-esp32-elf
 
-    CT_USE_SOURCES_FROM_NIXOS=y \
-      ct-ng build \
+    echo "CT_LOCAL_TARBALLS_DIR=$PWD/tarballs" >>.config
+    echo "CT_FORBID_DOWNLOAD=y" >>.config
+  '';
+
+  buildPhase = ''
+    export CT_USE_SOURCES_FROM_NIXOS=y
+    ct-ng build \
       || ( tail -n 100 build.log ; exit 1 )
   '';