clean up and add config for canadian cross builds

canadian.txt

-CT_TOOLCHAIN_TYPE="canadian"
-CT_BUILD="x86_64-unknown-linux-gnu"
-#CT_BUILD_PREFIX="x86_64-unknown-linux-gnu-"
-CT_BUILD_PREFIX="x86_64-unknown-linux-gnu-wrapped-"
-CT_HOST="aarch64-unknown-linux-gnu"
-CT_HOST_PREFIX="aarch64-unknown-linux-gnu-"
-
-unset CT_CROSS
-CT_CANADIAN=y
-
-CT_HOST_SUFFIX=
-
-#CT_CC_CORE_PASSES_NEEDED=y
-#CT_CC_CORE_PASS_1_NEEDED=y
-#CT_CC_GCC_STATIC_LIBSTDCXX=y

esp32-tools.nix

@@ -8,6 +8,14 @@ let
     ln -s ${pkg}/bin/gcc $out/bin/${pkg.stdenv.targetPlatform.config}-gcc
     ln -s ${pkg}/bin/gcc $out/bin/${pkg.stdenv.targetPlatform.config}-wrapped-gcc
   '';
+
+  # If Nix is cross-compiling this package, we have build!=host!=target (but Nix doesn't know about target, which is ESP32).
+  # This is called "canadian cross" for GCC builds and it needs some special care with crosstool-NG:
+  # 1. We need a working compiler for build-build. We cannot simply use the prefixed gcc name because that would
+  #    directly go to the gcc binary and skip the wrapper script. We create a prefixed variant of the wrapper script
+  #    with `wrapIt` and add this to depsBuildBuild.
+  # 2. We must tell crosstool-NG that we are building a canadian cross.
+  canadian = stdenv.buildPlatform != stdenv.hostPlatform;
 in stdenv.mkDerivation {
   pname = "espressif-esp32-tools";
   inherit (srcs) version srcs;
@@ -16,10 +24,9 @@ in stdenv.mkDerivation {
     (lib.attrsets.mapAttrsToList (name: drv: if drv ? outPath then "${name} ${drv.outPath}" else "") srcs2);
 
   buildInputs = [ ncurses python3 ];
-  depsBuildBuild = [ gcc binutils (wrapIt gcc.__spliced.buildBuild) ];
+  depsBuildBuild = if canadian then [ gcc binutils (wrapIt gcc.__spliced.buildBuild) ] else [ ];
   nativeBuildInputs = [ espressif-crosstool-ng autoconf automake bison flex unzip help2man libtool which texinfo file wget gnum4 perl python3 ]
     ++ [ breakpointHook ];
-  #  ++ [ (wrapIt gcc.__spliced.buildTarget) ];
 
   hardeningDisable = [ "format" "pie" ];
 
@@ -45,13 +52,18 @@ in stdenv.mkDerivation {
 
     echo "CT_LOCAL_TARBALLS_DIR=$PWD/tarballs" >>.config
     echo "CT_FORBID_DOWNLOAD=y" >>.config
-
-    sed -nE 's/^(.*-)g?cc$/CT_BUILD_PREFIX="\1"/p' <<<"$OLD_CC" >>.config
-  '';
-
-  #FIXME for cross-compiling
-  #  cat ../../canadian.txt >>.config
-  #  yes "" | ct-ng oldconfig
+  '' + (if !canadian then "" else ''
+    cat >>.config <<EOF
+    CT_TOOLCHAIN_TYPE="canadian"
+    unset CT_CROSS
+    CT_CANADIAN=y
+    CT_BUILD="${stdenv.buildPlatform.config}"
+    CT_BUILD_PREFIX="${stdenv.buildPlatform.config}-wrapped-"
+    CT_HOST="${stdenv.hostPlatform.config}"
+    CT_HOST_PREFIX="${stdenv.hostPlatform.config}-"
+    EOF
+    ( yes "" || true ) | ct-ng oldconfig
+  '');
 
   buildPhase = ''
     export CT_USE_SOURCES_FROM_NIXOS=y