From c19d19615c20844835b8729e21e038bc01f959c9 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Wed, 12 Jan 2022 08:48:49 +0000
Subject: [PATCH] buildRustCrate: Add support for standard library deps

We are replicating one mechanism behind `-Z build-std`.

There isn't yet crate2nix support for this, but one can (and I do) add
the missing stdlib deps (for this feature to pick up) with overrides.

(cherry picked from commit cc29693a0979c3b81da6942c214841ef11de95b5)
(cherry picked from commit 5aef865cefc2a906296b9a256bf597f70e4ee243)
---
 .../rust/build-rust-crate/build-crate.nix     |  8 ++++++-
 .../rust/build-rust-crate/default.nix         | 21 ++++++++++++++-----
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/pkgs/build-support/rust/build-rust-crate/build-crate.nix b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
index 42c5f6ab3c0f3..ddff0c13cb3ac 100644
--- a/pkgs/build-support/rust/build-rust-crate/build-crate.nix
+++ b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
@@ -1,4 +1,8 @@
-{ lib, stdenv, mkRustcDepArgs, mkRustcFeatureArgs, rust }:
+{ lib, stdenv
+, mkRustcDepArgs, mkRustcFeatureArgs, needUnstableCLI
+, rust
+}:
+
 { crateName,
   dependencies,
   crateFeatures, crateRenames, libName, release, libPath,
@@ -17,6 +21,8 @@
         (mkRustcFeatureArgs crateFeatures)
       ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
         "--target" (rust.toRustTargetSpec stdenv.hostPlatform)
+      ] ++ lib.optionals (needUnstableCLI dependencies) [
+        "-Z" "unstable-options"
       ] ++ extraRustcOpts
       # since rustc 1.42 the "proc_macro" crate is part of the default crate prelude
       # https://github.com/rust-lang/cargo/commit/4d64eb99a4#diff-7f98585dbf9d30aa100c8318e2c77e79R1021-R1022
diff --git a/pkgs/build-support/rust/build-rust-crate/default.nix b/pkgs/build-support/rust/build-rust-crate/default.nix
index 20b93b1921f84..68c52efc53f1d 100644
--- a/pkgs/build-support/rust/build-rust-crate/default.nix
+++ b/pkgs/build-support/rust/build-rust-crate/default.nix
@@ -46,17 +46,28 @@ let
               )
             else
               extern;
+          opts = lib.optionalString (dep.stdlib or false) "noprelude:";
+          filename =
+            if lib.any (x: x == "lib" || x == "rlib") dep.crateType
+            then "${dep.metadata}.rlib"
+            else "${dep.metadata}${stdenv.hostPlatform.extensions.sharedLibrary}";
         in
-        (if lib.any (x: x == "lib" || x == "rlib") dep.crateType then
-          " --extern ${name}=${dep.lib}/lib/lib${extern}-${dep.metadata}.rlib"
-        else
-          " --extern ${name}=${dep.lib}/lib/lib${extern}-${dep.metadata}${stdenv.hostPlatform.extensions.sharedLibrary}")
+        " --extern ${opts}${name}=${dep.lib}/lib/lib${extern}-${filename}"
       )
       dependencies;
 
   # Create feature arguments for rustc.
   mkRustcFeatureArgs = lib.concatMapStringsSep " " (f: ''--cfg feature=\"${f}\"'');
 
+  # Whether we need to use unstable command line flags
+  #
+  # Currently just needed for standard library dependencies, which have a
+  # special "noprelude:" modifier. If in later versions of Rust this is
+  # stabilized we can account for that here, too, so we don't opt into
+  # instability unnecessarily.
+  needUnstableCLI = dependencies:
+    lib.any (dep: dep.stdlib or false) dependencies;
+
   inherit (import ./log.nix { inherit lib; }) noisily echo_colored;
 
   configureCrate = import ./configure-crate.nix {
@@ -64,7 +75,7 @@ let
   };
 
   buildCrate = import ./build-crate.nix {
-    inherit lib stdenv mkRustcDepArgs mkRustcFeatureArgs rust;
+    inherit lib stdenv mkRustcDepArgs mkRustcFeatureArgs needUnstableCLI rust;
   };
 
   installCrate = import ./install-crate.nix { inherit stdenv; };