flutter: Redesign wrapping architecture

The following principles are now in place:

- All wrappers will include SDK file symlinks. There is not much of a reason to not do so, and removing the option to omit it makes it easier to understand what each wrapper does.
- There is no longer a way to get the previous derivation from a wrapper. This could yield unexpected results based on the wrapping order. Instead, "sdk", "unwrapped", and "noFHS" passthru attributes are provided where appropriate.

pkgs/development/compilers/flutter/default.nix

···
   mkFlutter = opts: callPackage (import ./flutter.nix opts) { };
   wrapFlutter = flutter: callPackage (import ./wrapper.nix) { flutter = flutter; };
   mkFlutterFHS = flutter: callPackage (import ./fhs.nix) { flutter = flutter; };
-  mkFakeSdk = flutter: callPackage (import ./fake-sdk.nix) { flutter = flutter; };
   getPatches = dir:
     let files = builtins.attrNames (builtins.readDir dir);
     in map (f: dir + ("/" + f)) files;
···
   };
 in
 {
-  inherit mkFlutter wrapFlutter mkFlutterFHS mkFakeSdk flutterDrv;
+  inherit mkFlutter wrapFlutter mkFlutterFHS flutterDrv;
   stable = flutterDrv {
     version = "3.3.3";
     dartVersion = "2.18.2";

pkgs/development/compilers/flutter/fake-sdk.nix

···
-{ flutter, symlinkJoin }:
-
-symlinkJoin {
-  name = "flutter-fake-${flutter.name}";
-  paths = [ flutter flutter.unwrapped ];
-
-  inherit (flutter) passthru;
-
-  meta = flutter.meta // {
-    longDescription = ''
-      ${flutter.meta.longDescription}
-      Modified binaries are linked into the original SDK directory for use with tools that use the whole SDK.
-    '';
-  };
-}

pkgs/development/compilers/flutter/fhs.nix

···
 , supportsAndroidEmulator ? stdenv.isLinux
 }:
 
-let
-  # Wrap flutter inside an fhs user env to allow execution of binary,
-  # like adb from $ANDROID_HOME or java from android-studio.
-  self = buildFHSUserEnv {
-    name = flutter.name;
 
-    multiPkgs = pkgs: with pkgs; ([
-      # Flutter only use these certificates
-      (runCommandLocal "fedoracert" { } ''
-        mkdir -p $out/etc/pki/tls/
-        ln -s ${cacert}/etc/ssl/certs $out/etc/pki/tls/certs
-      '')
-      zlib
-    ]);
+# Wrap flutter inside an fhs user env to allow execution of binary,
+# like adb from $ANDROID_HOME or java from android-studio.
+(callPackage ./sdk-symlink.nix { }) (buildFHSUserEnv rec {
+  name = "${flutter.name}-fhs";
 
-    targetPkgs = pkgs: with pkgs; ([
-      flutter
+  multiPkgs = pkgs: with pkgs; ([
+    # Flutter only use these certificates
+    (runCommandLocal "fedoracert" { } ''
+      mkdir -p $out/etc/pki/tls/
+      ln -s ${cacert}/etc/ssl/certs $out/etc/pki/tls/certs
+    '')
+    zlib
+  ]);
 
-      # General ecosystem dependencies
-      bash
-      curl
-      git
-      unzip
-      which
-      xz
+  targetPkgs = pkgs: with pkgs; ([
+    flutter
 
-      # flutter test requires this lib
-      libGLU
-    ] ++ lib.optional supportsAndroidEmulator [
-      # for android emulator
-      alsa-lib
-      dbus
-      expat
-      libpulseaudio
-      libuuid
-      xorg.libX11
-      xorg.libxcb
-      xorg.libXcomposite
-      xorg.libXcursor
-      xorg.libXdamage
-      xorg.libXext
-      xorg.libXfixes
-      xorg.libXi
-      xorg.libXrender
-      xorg.libXtst
-      libGL
-      nspr
-      nss
-      systemd
-    ]);
+    # General ecosystem dependencies
+    bash
+    curl
+    git
+    unzip
+    which
+    xz
 
-    runScript = "flutter";
+    # flutter test requires this lib
+    libGLU
+  ] ++ lib.optional supportsAndroidEmulator [
+    # for android emulator
+    alsa-lib
+    dbus
+    expat
+    libpulseaudio
+    libuuid
+    xorg.libX11
+    xorg.libxcb
+    xorg.libXcomposite
+    xorg.libXcursor
+    xorg.libXdamage
+    xorg.libXext
+    xorg.libXfixes
+    xorg.libXi
+    xorg.libXrender
+    xorg.libXtst
+    libGL
+    nspr
+    nss
+    systemd
+  ]);
+
+  runScript = "flutter";
+
+  extraInstallCommands = ''
+    # By default, the derivation name is used as the binary name.
+    # This is not the desired behaviour in this case.
+    # https://github.com/NixOS/nixpkgs/blob/cb4536bf3606a7b6b54b69afe22ccd82e2906d92/pkgs/build-support/build-fhs-userenv/default.nix#L43
+    mv $out/bin/${name} $out/bin/flutter
+  '';
 
-    passthru = flutter.passthru // {
-      wrapped = flutter;
-      mkFlutterApp = callPackage ../../../build-support/flutter {
-        flutter = callPackage ./fhs.nix { supportsAndroidEmulator = false; };
-      };
-      fakeSdk = callPackage ./fake-sdk.nix { flutter = self; };
+  passthru = flutter.passthru // {
+    nonFHS = flutter;
+    mkFlutterApp = callPackage ../../../build-support/flutter {
+      flutter = callPackage ./fhs.nix { supportsAndroidEmulator = false; };
     };
+  };
 
-    meta = flutter.meta // {
-      longDescription = ''
-        ${flutter.meta.longDescription}
-        Wrapped in a FHS environment to improve compatibility with internal tools and tools in the ecosystem.
-      '';
-    };
+  meta = flutter.meta // {
+    longDescription = ''
+      ${flutter.meta.longDescription}
+      Wrapped in a FHS environment to improve compatibility with internal tools and tools in the ecosystem.
+    '';
   };
-in
-self
+})

pkgs/development/compilers/flutter/flutter.nix

···
 , which
 }:
 
-stdenv.mkDerivation {
-  name = "$flutter-${version}-unwrapped";
+let
+  self =
+    stdenv.mkDerivation {
+      name = "$flutter-${version}-unwrapped";
 
-  buildInputs = [ git ];
+      buildInputs = [ git ];
 
-  inherit src patches version;
+      inherit src patches version;
 
-  postPatch = ''
-    patchShebangs --build ./bin/
-  '';
+      postPatch = ''
+        patchShebangs --build ./bin/
+      '';
 
-  buildPhase = ''
-    export FLUTTER_ROOT="$(pwd)"
-    export FLUTTER_TOOLS_DIR="$FLUTTER_ROOT/packages/flutter_tools"
-    export SCRIPT_PATH="$FLUTTER_TOOLS_DIR/bin/flutter_tools.dart"
+      buildPhase = ''
+        export FLUTTER_ROOT="$(pwd)"
+        export FLUTTER_TOOLS_DIR="$FLUTTER_ROOT/packages/flutter_tools"
+        export SCRIPT_PATH="$FLUTTER_TOOLS_DIR/bin/flutter_tools.dart"
 
-    export SNAPSHOT_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.snapshot"
-    export STAMP_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.stamp"
+        export SNAPSHOT_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.snapshot"
+        export STAMP_PATH="$FLUTTER_ROOT/bin/cache/flutter_tools.stamp"
 
-    export DART_SDK_PATH="${dart}"
+        export DART_SDK_PATH="${dart}"
 
-    HOME=../.. # required for pub upgrade --offline, ~/.pub-cache
-               # path is relative otherwise it's replaced by /build/flutter
+        HOME=../.. # required for pub upgrade --offline, ~/.pub-cache
+                   # path is relative otherwise it's replaced by /build/flutter
 
-    pushd "$FLUTTER_TOOLS_DIR"
-    ${dart}/bin/dart pub get --offline
-    popd
+        pushd "$FLUTTER_TOOLS_DIR"
+        ${dart}/bin/dart pub get --offline
+        popd
 
-    local revision="$(cd "$FLUTTER_ROOT"; git rev-parse HEAD)"
-    ${dart}/bin/dart --snapshot="$SNAPSHOT_PATH" --packages="$FLUTTER_TOOLS_DIR/.dart_tool/package_config.json" "$SCRIPT_PATH"
-    echo "$revision" > "$STAMP_PATH"
-    echo -n "${version}" > version
+        local revision="$(cd "$FLUTTER_ROOT"; git rev-parse HEAD)"
+        ${dart}/bin/dart --snapshot="$SNAPSHOT_PATH" --packages="$FLUTTER_TOOLS_DIR/.dart_tool/package_config.json" "$SCRIPT_PATH"
+        echo "$revision" > "$STAMP_PATH"
+        echo -n "${version}" > version
 
-    rm -r bin/cache/{artifacts,dart-sdk,downloads}
-    rm bin/cache/*.stamp
-  '';
+        rm -r bin/cache/{artifacts,dart-sdk,downloads}
+        rm bin/cache/*.stamp
+      '';
 
-  installPhase = ''
-    runHook preInstall
+      installPhase = ''
+        runHook preInstall
 
-    mkdir -p $out
-    cp -r . $out
-    mkdir -p $out/bin/cache/
-    ln -sf ${dart} $out/bin/cache/dart-sdk
+        mkdir -p $out
+        cp -r . $out
+        mkdir -p $out/bin/cache/
+        ln -sf ${dart} $out/bin/cache/dart-sdk
 
-    runHook postInstall
-  '';
+        runHook postInstall
+      '';
 
-  doInstallCheck = true;
-  installCheckInputs = [ which ];
-  installCheckPhase = ''
-    runHook preInstallCheck
+      doInstallCheck = true;
+      installCheckInputs = [ which ];
+      installCheckPhase = ''
+        runHook preInstallCheck
 
-    export HOME="$(mktemp -d)"
-    $out/bin/flutter config --android-studio-dir $HOME
-    $out/bin/flutter config --android-sdk $HOME
-    $out/bin/flutter --version | fgrep -q '${version}'
+        export HOME="$(mktemp -d)"
+        $out/bin/flutter config --android-studio-dir $HOME
+        $out/bin/flutter config --android-sdk $HOME
+        $out/bin/flutter --version | fgrep -q '${version}'
 
-    runHook postInstallCheck
-  '';
+        runHook postInstallCheck
+      '';
 
-  passthru = {
-    inherit dart;
-  };
+      passthru = {
+        inherit dart;
 
-  meta = with lib; {
-    description = "Flutter is Google's SDK for building mobile, web and desktop with Dart";
-    longDescription = ''
-      Flutter is Google’s UI toolkit for building beautiful,
-      natively compiled applications for mobile, web, and desktop from a single codebase.
-    '';
-    homepage = "https://flutter.dev";
-    license = licenses.bsd3;
-    platforms = [ "x86_64-linux" "aarch64-linux" ];
-    maintainers = with maintainers; [ babariviere ericdallo ];
-  };
-}
+        # The derivation containing the original Flutter SDK files.
+        # When other derivations wrap this one, any unmodified files
+        # found here should be included as-is, for tooling compatibility.
+        sdk = self;
+      };
+
+      meta = with lib; {
+        description = "Flutter is Google's SDK for building mobile, web and desktop with Dart";
+        longDescription = ''
+          Flutter is Google’s UI toolkit for building beautiful,
+          natively compiled applications for mobile, web, and desktop from a single codebase.
+        '';
+        homepage = "https://flutter.dev";
+        license = licenses.bsd3;
+        platforms = [ "x86_64-linux" "aarch64-linux" ];
+        maintainers = with maintainers; [ babariviere ericdallo ];
+      };
+    }
+  ;
+in
+self

pkgs/development/compilers/flutter/sdk-symlink.nix

···
+{ symlinkJoin }: flutter:
+
+let
+  self =
+    symlinkJoin {
+      name = "${flutter.name}-sdk-links";
+      paths = [ flutter flutter.sdk ];
+
+      passthru = flutter.passthru // {
+        # Update the SDK attribute.
+        # This allows any modified SDK files to be included
+        # in future invocations.
+        sdk = self;
+      };
+
+      meta = flutter.meta // {
+        longDescription = ''
+          ${flutter.meta.longDescription}
+          Modified binaries are linked into the original SDK directory for use with tools that use the whole SDK.
+        '';
+      };
+    };
+in
+self

pkgs/development/compilers/flutter/wrapper.nix

···
   cppFlags = map (pkg: "-isystem ${lib.getOutput "dev" pkg}/include") appStaticBuildDeps;
   linkerFlags = map (pkg: "-rpath,${lib.getOutput "lib" pkg}/lib") appRuntimeDeps;
 in
-runCommandLocal "flutter"
+(callPackage ./sdk-symlink.nix { }) (runCommandLocal "flutter-wrapped"
 {
   buildInputs = [ makeWrapper ];
 
···
   inherit (flutter) meta;
 } ''
   mkdir -p $out/bin
-
-  mkdir -p $out/bin/cache/
-  ln -sf ${flutter.dart} $out/bin/cache/dart-sdk
-
   makeWrapper '${immutableFlutter}' $out/bin/flutter \
     --set-default ANDROID_EMULATOR_USE_SYSTEM_LIBS 1 \
     --prefix PATH : '${lib.makeBinPath buildTools}' \
···
     --prefix CXXFLAGS "''\t" '${builtins.concatStringsSep " " cppFlags}' \
     --prefix LDFLAGS "''\t" '${builtins.concatStringsSep " " (map (flag: "-Wl,${flag}") linkerFlags)}' \
     --suffix LD_LIBRARY_PATH : '${lib.makeLibraryPath appPrebuiltDeps}'
-''
+'')