rust: support dependency-based env overrides for build scripts

lang/rust/src/resolver.sld

@@ -43,13 +43,15 @@
    (define openssl (delay (let ((data (nixpkgs "openssl"))) #~,(begin #$(cdr (assoc "out" data)) #$(cdr (assoc "dev" data))))))
    (define tvix-protos (delay (vfs-to-store (vfs-from-directory "/home/nix/store/dkjgsrg8knn406qh86c3mbxpbz2rjwfy-tvix-all-protos"))))
 
-   (define (build-script-env-overrides-for-crate crate-name)
+   (define (build-script-env-overrides-for-crate crate-name is-dependency)
      (cond
-      ((string=? crate-name "openssl-sys")
+      ((and (string=? crate-name "pkg-config") is-dependency)
-       #~(("PATH" . ,(string-append #$(force pkgconfig) "/bin:" #$(force gcc) "/bin")) ("PKG_CONFIG_PATH" . ,(string-append #$(force openssl) "/lib/pkgconfig"))))
+       #~(("PATH" . ,(string-append #$(force pkgconfig) "/bin"))))
-      ((or (string=? crate-name "ring") (string=? crate-name "bzip2-sys") (string=? crate-name "zstd-sys") (string=? crate-name "lzma-sys") (string=? crate-name "libmimalloc-sys"))
+      ((and (string=? crate-name "openssl-sys") (not is-dependency))
+       #~(("PATH" . ,(string-append #$(force gcc) "/bin")) ("PKG_CONFIG_PATH" . ,(string-append #$(force openssl) "/lib/pkgconfig"))))
+      ((and (member crate-name '("ring" "bzip2-sys" "zstd-sys" "lzma-sys" "libmimalloc-sys") string=?) (not is-dependency))
        #~(("PATH" . ,(string-append #$(force gcc) "/bin"))))
-      ((or (string=? crate-name "tvix-castore") (string=? crate-name "tvix-store") (string=? crate-name "tvix-build"))
+      ((and (member crate-name '("tvix-castore" "tvix-store" "tvix-build") string=?) (not is-dependency))
        #~(("PATH" . ,(string-append #$(force protobuf) "/bin")) ("PROTO_ROOT" . #$(force tvix-protos))))
       ((or (string=? crate-name "prost-wkt-types") (string=? crate-name "nar-bridge"))
        #~(("PATH" . ,(string-append #$(force protobuf) "/bin"))))
@@ -286,6 +288,21 @@
     ; TODO(puck): check this post-C6
     (string-map (lambda (v) (if (char=? v #\-) #\_ v)) name))
 
+   (define (rewrite-env envs)
+     (define final-env (mapping (make-default-comparator)))
+     (for-each
+      (lambda (vars)
+       (for-each
+        (lambda (env-block)
+         (define value (mapping-ref/default final-env (car env-block) #f))
+         (if value
+          (set! value (string-append (cdr env-block) ":" value))
+          (set! value (cdr env-block)))
+         (set! final-env (mapping-set! final-env (car env-block) value)))
+        vars))
+      (reverse envs))
+     (mapping-map->list (lambda (k v) (cons k v)) final-env))
+
    (define (build-package resolved)
      ; Info we need to collect:
      ; - enabled features
@@ -361,18 +378,25 @@
              (make-cfg-values-env (cdr l) (cons (cons env-name (or (cdar l) "")) out)))))
         (else out)))
 
+     (define build-script-envs #f)
+
      (when (resolved-package-build-script resolved)
        ;; "build" here is a misnomer; it's handling the .drv:s.
        (unless (resolved-package-build-data (resolved-package-build-script resolved))
          (build-package (resolved-package-build-script resolved)))
 
-       ; For each package dependency, check if it has "links" metadata.
+       (set! build-script-envs (list (build-script-env-overrides-for-crate (cargo-crate-name (resolved-package-crate resolved)) #f)))
+
+       ; For each package dependency, check if it has "links" metadata, as well as build script env overrides.
        ; Crate that immediately depend on other crates that have this metadata have
        ; the cargo::metadata pairs passed to the build script.
        (mapping-for-each
          (lambda (key value)
            (unless (resolved-package-build-data value)
              (build-package value))
+           (let ((env-override (build-script-env-overrides-for-crate (cargo-crate-name (resolved-package-crate value)) #t)))
+             (when env-override
+               (set! build-script-envs (cons env-override build-script-envs))))
            (when (cargo-crate-links (resolved-package-crate value))
              ; Track (link-name . build-data) for each crate in immediate dependencies that applies
              (set! crate-links (cons (cons (cargo-crate-links (resolved-package-crate value)) (resolved-package-build-data value)) crate-links))))
@@ -381,7 +405,6 @@
        ; Collect the necessary bits, and build the build script.
        (let*-values
          (((build-script) (cdr (resolved-package-build-data-rlib (resolved-package-build-data (resolved-package-build-script resolved)))))
-          ((build-script-env) (build-script-env-overrides-for-crate (cargo-crate-name (resolved-package-crate resolved))))
           ((rewritten-features) (map (lambda (feature) (cons (string-map upcase-underscore (string-append "CARGO_FEATURE_" feature)) "")) (resolved-package-enabled-features resolved)))
           ((runner-outdir runner-outpath)
            (call-runner build-script crate-root
@@ -396,7 +419,7 @@
                 ,@(make-cfg-values-env cfg-values '())
                 ,@dependency-metadata
                 ,@rewritten-features
-                #$@build-script-env
+                ,@(rewrite-env #$build-script-envs)
                 ; TODO: OUT_DIR, NUM_JOBS, OPT_LEVEL/DEBUG/PROFILE
                 ; RUSTC/RUSTDOC?, RUSTC_LINKER? and CARGO_ENCODED_RUSTFLAGS
                 . #$rustc-env))))