Empty RUSTFLAGS are still set

[delehef]

Describe the bug

Even if the computed value is empty, the RUSTFLAGS env. var. is still set when activating rust with languages.rust.enable = true;.

However, an empty RUSTFLAGS env. var. inhibits any rust flags that may have been set in .cargo/config.toml.

To reproduce
Set some rust flags in the [build] section of .cargo/config.toml, do not alter languages.rust.rustflags, and enable the rust environment with languages.rust.enable = true;.

Version

devenv 1.1.0

[domenkozar]

Could you test #1498

[clotodex]

could this be related in any way? #1419
I am thinking if this is afffecting more than just rustflags or if there are any cross-effects?

[delehef]

@domenkozar this unfortunately does not work, as it appears that lib.mkIf is not compatible with the environment variables creation method. However, I slightly modified your PR with the joined patch, and I made it work (at least on my machine).

diff --git a/src/modules/languages/rust.nix b/src/modules/languages/rust.nix
index dcbd03c..339088c 100644
--- a/src/modules/languages/rust.nix
+++ b/src/modules/languages/rust.nix
@@ -128,15 +128,15 @@ in
         env =
           let
             moldFlags = lib.optionalString cfg.mold.enable "-C link-arg=-fuse-ld=mold";
-          in
-          {
+          in
+          lib.attrsets.filterAttrs (_: value: (lib.stringLength value) > 0) {
             # RUST_SRC_PATH is necessary when rust-src is not at the same location as
             # as rustc. This is the case with the rust toolchain from nixpkgs.
             RUST_SRC_PATH =
               if cfg.toolchain ? rust-src
               then "${cfg.toolchain.rust-src}/lib/rustlib/src/rust/library"
               else pkgs.rustPlatform.rustLibSrc;
-            RUSTFLAGS = lib.mkIf (moldFlags != "" || cfg.rustflags != "") (lib.concatStringsSep " " (lib.filter (x: x != "") [moldFlags cfg.rustflags]));
+            RUSTFLAGS = (lib.concatStringsSep " " (lib.filter (x: x != "") [moldFlags cfg.rustflags]));
             RUSTDOCFLAGS = moldFlags;
             CFLAGS = lib.optionalString pkgs.stdenv.isDarwin "-iframework ${config.devenv.profile}/Library/Frameworks";
           };

[domenkozar]

@delehef we can't dynamically filter env because that creates recursion errors.

I've pushed a fix that sets it to null, which should make sure it's not set. Can you try again?

[delehef]

because that creates recursion errors.

Just FYI, I tested it on my side and it didn't fail; I suppose you would need to alter env from multiple sides to see these errors come into play?

Can you try again?

This one seems to work fine :)

[domenkozar]

Alright merged, thanks!