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Add automatic C library input propagation workaround

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Automatically adds Nix C library build inputs based on which nix-bindings
crates are dependencies, working around missing native input propagation
in nix-cargo-integration.

The workaround inspects the dreamLock to detect:
- If the crate being built is a nix-bindings crate (adds its own inputs)
- Direct dependencies on nix-bindings crates (adds their inputs)

The mapping is recursive via lazyAttrsOf, so depending on nix-bindings-flake
automatically brings in transitive C library dependencies.

Downstream consumers can extend the mapping for their own multi-crate
workspaces where crate A depends on crate B which depends on nix-bindings.
This commit is contained in:
Robert Hensing 2026-01-13 15:25:57 +01:00
parent dbb00333b1
commit 6110414520
3 changed files with 156 additions and 66 deletions
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25
flake.nix
View file

@ -28,6 +28,7 @@
}:
{
_file = ./flake.nix;
imports = [ ./input-propagation-workaround.nix ];
options.perSystem = flake-parts-lib.mkPerSystemOption (
{ pkgs, ... }:
{
@ -46,24 +47,20 @@
A module to load into your nix-cargo-integration
[`perSystem.nci.projects.<name>.depsDrvConfig`](https://flake.parts/options/nix-cargo-integration.html#opt-perSystem.nci.projects._name_.depsDrvConfig) or similar such options.
This provides common build configuration (pkg-config, libclang, etc.) but you must
add the specific Nix C libraries your crates need to `buildInputs`:
- `nix-bindings-util-sys` needs `nix-util-c`
- `nix-bindings-store-sys` needs `nix-store-c`
- `nix-bindings-expr-sys` needs `nix-expr-c`
- `nix-bindings-fetchers-sys` needs `nix-fetchers-c` (Nix >= 2.29)
- `nix-bindings-flake-sys` needs `nix-flake-c`
- `nix-bindings-bdwgc-sys` needs `boehmgc`
This provides common build configuration (pkg-config, libclang, etc.) and
automatically adds Nix C library build inputs based on which nix-bindings
crates are *direct* dependencies of your crate.
To disable automatic build input detection:
```nix
nix-bindings-rust.inputPropagationWorkaround.enable = false;
```
Example:
```nix
perSystem = perSystem@{ config, pkgs, ... }: {
nci.projects."my_project".depsDrvConfig = {
perSystem = perSystem@{ config, ... }: {
nci.projects."my_project".drvConfig = {
imports = [ perSystem.config.nix-bindings-rust.nciBuildConfig ];
mkDerivation.buildInputs = [
perSystem.config.nix-bindings-rust.nixPackage.libs.nix-store-c
# ... add other libs as needed
];
};
}
```

143
input-propagation-workaround.nix Normal file
View file

@ -0,0 +1,143 @@
# Workaround for missing native input propagation in nix-cargo-integration
#
# Automatically adds Nix C library build inputs based on which nix-bindings
# crates are direct dependencies of the crate being built. The mapping is
# recursive, so depending on nix-bindings-flake will also bring in the
# transitive C library dependencies (nix-fetchers-c, nix-expr-c, etc.).
#
# Note: For multi-crate workspaces, if your crate A depends on your crate B
# which depends on nix-bindings, you'll need to add an A -> B mapping to
# `crateInputMapping` so that A also gets B's nix-bindings inputs.
{
perSystem =
{
lib,
config,
pkgs,
...
}:
let
cfg = config.nix-bindings-rust.inputPropagationWorkaround;
nixPackage = config.nix-bindings-rust.nixPackage;
nixLibs =
if nixPackage ? libs then
nixPackage.libs
else
# Fallback for older Nix versions without split libs
{
nix-util-c = nixPackage;
nix-store-c = nixPackage;
nix-expr-c = nixPackage;
nix-fetchers-c = nixPackage;
nix-flake-c = nixPackage;
};
# A module for nciBuildConfig that sets buildInputs based on nix-bindings dependencies.
# Uses options inspection to detect drvConfig vs depsDrvConfig context.
workaroundModule =
{
lib,
config,
options,
...
}:
let
# rust-cargo-lock exists in drvConfig but not depsDrvConfig
isDrvConfig = options ? rust-cargo-lock;
dreamLock = config.rust-cargo-lock.dreamLock;
depsList = dreamLock.dependencies.${config.name}.${config.version} or [ ];
# Convert list of deps to attrset keyed by name for efficient lookup
deps = builtins.listToAttrs (
map (dep: {
name = dep.name;
value = dep;
}) depsList
);
# Inputs for the crate itself if it's in the mapping
selfInputs = cfg.crateInputMapping.${config.name} or [ ];
# Inputs for direct dependencies that have mappings
depInputs = lib.concatLists (lib.attrValues (lib.intersectAttrs deps cfg.crateInputMapping));
allInputs = selfInputs ++ depInputs;
in
{
config = lib.optionalAttrs isDrvConfig {
mkDerivation.buildInputs = allInputs;
rust-crane.depsDrv.mkDerivation.buildInputs = allInputs;
};
};
in
{
options.nix-bindings-rust.inputPropagationWorkaround = {
enable = lib.mkOption {
type = lib.types.bool;
default = true;
description = ''
Whether to automatically add Nix C library build inputs based on
which nix-bindings crates are direct dependencies.
Set to `false` to disable automatic detection and specify buildInputs manually.
'';
};
crateInputMapping = lib.mkOption {
type = lib.types.lazyAttrsOf (lib.types.listOf lib.types.package);
description = ''
Mapping from crate names to build inputs. Entries can reference
other entries for transitive dependencies.
The input propagation workaround can see direct dependencies, so
if you have `my-crate -> nix-bindings`, that works out of the box.
If you have `my-other-crate -> my-crate -> nix-bindings`, then you
need to specify `my-other-crate -> my-crate` as follows:
```nix
nix-bindings-rust.inputPropagationWorkaround.crateInputMapping."my-other-crate" =
config.nix-bindings-rust.inputPropagationWorkaround.crateInputMapping."my-crate";
```
'';
default = { };
};
};
config = lib.mkIf cfg.enable {
nix-bindings-rust.inputPropagationWorkaround.crateInputMapping = {
# -sys crates with their transitive dependencies
"nix-bindings-bdwgc-sys" = [ pkgs.boehmgc ];
"nix-bindings-util-sys" = [ nixLibs.nix-util-c.dev ];
"nix-bindings-store-sys" = [
nixLibs.nix-store-c.dev
]
++ cfg.crateInputMapping."nix-bindings-util-sys";
"nix-bindings-expr-sys" = [
nixLibs.nix-expr-c.dev
]
++ cfg.crateInputMapping."nix-bindings-store-sys"
++ cfg.crateInputMapping."nix-bindings-bdwgc-sys";
"nix-bindings-fetchers-sys" = [
nixLibs.nix-fetchers-c.dev
]
++ cfg.crateInputMapping."nix-bindings-expr-sys";
"nix-bindings-flake-sys" = [
nixLibs.nix-flake-c.dev
]
++ cfg.crateInputMapping."nix-bindings-fetchers-sys"
++ cfg.crateInputMapping."nix-bindings-bdwgc-sys";
# High-level crates reference their -sys counterparts
"nix-bindings-bdwgc" = cfg.crateInputMapping."nix-bindings-bdwgc-sys";
"nix-bindings-util" = cfg.crateInputMapping."nix-bindings-util-sys";
"nix-bindings-store" = cfg.crateInputMapping."nix-bindings-store-sys";
"nix-bindings-expr" = cfg.crateInputMapping."nix-bindings-expr-sys";
"nix-bindings-fetchers" = cfg.crateInputMapping."nix-bindings-fetchers-sys";
"nix-bindings-flake" = cfg.crateInputMapping."nix-bindings-flake-sys";
};
nix-bindings-rust.nciBuildConfig.imports = [ workaroundModule ];
};
};
}

54
nci.nix
View file

@ -1,24 +1,8 @@
{
perSystem =
{
config,
pkgs,
...
}:
{ config, ... }:
let
cfg = config.nix-bindings-rust;
nixLibs =
if cfg.nixPackage ? libs then
cfg.nixPackage.libs
else
# Fallback for older Nix versions without split libs
{
nix-util-c = cfg.nixPackage;
nix-store-c = cfg.nixPackage;
nix-expr-c = cfg.nixPackage;
nix-fetchers-c = cfg.nixPackage;
nix-flake-c = cfg.nixPackage;
};
in
{
# https://flake.parts/options/nix-cargo-integration
@ -31,7 +15,7 @@
drvConfig = {
imports = [
# Downstream projects import this into depsDrvConfig instead
config.nix-bindings-rust.nciBuildConfig
cfg.nciBuildConfig
];
# Extra settings for running the tests
mkDerivation = {
@ -65,39 +49,5 @@
};
};
};
# Per-crate configuration: only provide the specific Nix libs each crate needs
# FIXME should use propagatedBuildInputs
nci.crates.nix-bindings-bdwgc-sys.drvConfig.mkDerivation.buildInputs = [
pkgs.boehmgc
];
nci.crates.nix-bindings-util-sys.drvConfig.mkDerivation.buildInputs = [
nixLibs.nix-util-c
];
nci.crates.nix-bindings-util.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-util-sys.drvConfig.mkDerivation.buildInputs;
nci.crates.nix-bindings-store-sys.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-util-sys.drvConfig.mkDerivation.buildInputs
++ [ nixLibs.nix-store-c ];
nci.crates.nix-bindings-store.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-store-sys.drvConfig.mkDerivation.buildInputs;
nci.crates.nix-bindings-expr-sys.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-store-sys.drvConfig.mkDerivation.buildInputs
++ [
nixLibs.nix-expr-c
pkgs.boehmgc
];
nci.crates.nix-bindings-expr.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-expr-sys.drvConfig.mkDerivation.buildInputs;
nci.crates.nix-bindings-fetchers-sys.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-expr-sys.drvConfig.mkDerivation.buildInputs
++ [ nixLibs.nix-fetchers-c ];
nci.crates.nix-bindings-fetchers.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-fetchers-sys.drvConfig.mkDerivation.buildInputs;
nci.crates.nix-bindings-flake-sys.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-fetchers-sys.drvConfig.mkDerivation.buildInputs
++ [ nixLibs.nix-flake-c ];
nci.crates.nix-bindings-flake.drvConfig.mkDerivation.buildInputs =
config.nci.crates.nix-bindings-flake-sys.drvConfig.mkDerivation.buildInputs;
};
}