fectchcargo: don't break old sha256

doc/languages-frameworks/rust.section.md

···
     sha256 = "0y5d1n6hkw85jb3rblcxqas2fp82h3nghssa4xqrhqnz25l799pj";
   };
 
-  cargoSha256 = "194lzn9xjkc041lmqnm676ydgbhn45xx9jhrhz6lzlg99yr6b880";
-  useRealVendorConfig = true;
+  cargoSha256 = "0q68qyl2h6i0qsz82z840myxlnjay8p1w5z7hfyr8fqp7wgwa9cx";
 
   meta = with stdenv.lib; {
     description = "A fast line-oriented regex search tool, similar to ag and ack";
···
 `Cargo.toml`, it is possible to use `cargoPatches` to update it. All patches
 added in `cargoPatches` will also be prepended to the patches in `patches` at
 build-time.
-
-The `useRealVendorConfig` parameter tells cargo-vendor to include a Cargo
-configuration file in the fetched dependencies. This will fix problems with
-projects, where Crates are downloaded from non-crates.io sources. Please note,
-that currently this parameter defaults to `false` only due to compatibility
-reasons, as setting this to `true` requires a change in `cargoSha256`.
-Eventually this distinction will be deprecated, so please always set
-`useRealVendorConfig` to `true` and make sure to recompute the `cargoSha256`.
 
 To install crates with nix there is also an experimental project called
 [nixcrates](https://github.com/fractalide/nixcrates).

nixos/doc/manual/release-notes/rl-1809.xml

···
       <literal>stdenv.buildPlatform</literal>, <literal>stdenv.hostPlatform</literal>, and <literal>stdenv.targetPlatform</literal>.
     </para>
   </listitem>
-  <listitem>
-    <para>
-	    The <literal>buildRustPackage</literal> function got the new
-	    argument <literal>useRealVendorConfig</literal>, currently
-	    defaulting to <literal>false</literal>. Setting it to
-	    <literal>true</literal> necessates the recomputation of the
-	    <literal>cargoSha256</literal> and fixes a problem with
-	    dependencies, that were fetched from a non-crates.io source.
-	    Eventually only the <literal>true</literal> behaviour will be kept,
-	    so please set it explicitly to <literal>true</literal> and
-	    recompute your <literal>cargoSha256</literal>, so that we can
-	    migrate to the new behaviour and deprecate the option.
-    </para>
-    <para>
-	    While recomputing <literal>cargoSha256</literal>, it is important
-	    to first invalidate the hash (e.g. by changing a digit), so that
-	    Nix actually rebuilds the fixed-output derivation. Otherwise this
-	    could lead to hard to detect errors, where a package seemingly
-	    builds on your computer, but breaks on others!
-    </para>
-  </listitem>
   </itemizedlist>
  </section>
 </section>

pkgs/build-support/rust/default.nix

···
 , cargoBuildFlags ? []
 
 , cargoVendorDir ? null
-# This tells cargo-vendor to include a Cargo config file in the fixed-output
-# derivation. This is desirable in every case, so please set it to true.
-# Eventually this will default to true and even later this option and the old
-# behaviour will be removed.
-, useRealVendorConfig ? false
 , ... } @ args:
 
 assert cargoVendorDir == null -> cargoSha256 != "unset";
-assert cargoVendorDir != null -> !useRealVendorConfig;
 
 let
   cargoDeps = if cargoVendorDir == null
···
         inherit name src srcs sourceRoot cargoUpdateHook;
         patches = cargoPatches;
         sha256 = cargoSha256;
-        writeVendorConfig = useRealVendorConfig;
       }
     else null;
 
···
     ${setupVendorDir}
 
     mkdir .cargo
-  '' + (if useRealVendorConfig then ''
-      substitute "$(pwd)/$cargoDepsCopy/.cargo/config" .cargo/config \
-      --subst-var-by vendor "$(pwd)/$cargoDepsCopy"
-    '' else ''
-      cat >.cargo/config <<-EOF
-        [source.crates-io]
-        registry = 'https://github.com/rust-lang/crates.io-index'
-        replace-with = 'vendored-sources'
-
-        [source.vendored-sources]
-        directory = '$(pwd)/$cargoDepsCopy'
-      EOF
-    '') + ''
+    config="$(pwd)/$cargoDepsCopy/.cargo/config";
+    if [[ ! -e $config ]]; then
+      config=${./fetchcargo-default-config.toml};
+    fi;
+    substitute $config .cargo/config \
+    --subst-var-by vendor "$(pwd)/$cargoDepsCopy"
 
     unset cargoDepsCopy
 

pkgs/build-support/rust/fetchcargo-default-config.toml

···
+[source."crates-io"]
+"replace-with" = "vendored-sources"
+
+[source."vendored-sources"]
+"directory" = "@vendor@"
+
+

pkgs/build-support/rust/fetchcargo.nix

···
 { stdenv, cacert, git, rust, cargo-vendor, python3 }:
-{ name ? "cargo-deps", src, srcs, patches, sourceRoot, sha256, cargoUpdateHook ? "", writeVendorConfig ? false }:
 let cargo-vendor-normalise = stdenv.mkDerivation {
   name = "cargo-vendor-normalise";
   src = ./cargo-vendor-normalise.py;
···
   preferLocalBuild = true;
 };
 in
+{ name ? "cargo-deps", src, srcs, patches, sourceRoot, sha256, cargoUpdateHook ? "" }:
 stdenv.mkDerivation {
   name = "${name}-vendor";
-  nativeBuildInputs = [ cacert cargo-vendor git rust.cargo ];
+  nativeBuildInputs = [ cacert cargo-vendor git cargo-vendor-normalise rust.cargo ];
   inherit src srcs patches sourceRoot;
 
   phases = "unpackPhase patchPhase installPhase";
···
     ${cargoUpdateHook}
 
     mkdir -p $out
-    cargo vendor $out > config
-  '' + stdenv.lib.optionalString writeVendorConfig ''
-    mkdir $out/.cargo
-    < config ${cargo-vendor-normalise}/bin/cargo-vendor-normalise > $out/.cargo/config
+    cargo vendor $out | cargo-vendor-normalise > config
+    # fetchcargo used to never keep the config output by cargo vendor
+    # and instead hardcode the config in ./fetchcargo-default-config.toml.
+    # This broke on packages needing git dependencies, so now we keep the config.
+    # But not to break old cargoSha256, if the previous behavior was enough,
+    # we don't store the config.
+    if ! cmp config ${./fetchcargo-default-config.toml} > /dev/null; then
+      install -Dt $out/.cargo config;
+    fi;
   '';
 
   outputHashAlgo = "sha256";