gnu: Add rust-cargo-metadata-0.15.

* gnu/packages/crates-io.scm (rust-cargo-metadata-0.15): New variable.
(rust-cargo-metadata-0.14): Inherit from rust-cargo-metadata-0.15.

gnu/packages/crates-io.scm

@@ -9344,8 +9344,46 @@ capabilities.")
 the library crate of Cargo.")
     (license (list license:expat license:asl2.0))))
 
+(define-public rust-cargo-metadata-0.15
+  (package
+    (name "rust-cargo-metadata")
+    (version "0.15.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (crate-uri "cargo-metadata" version))
+       (file-name
+        (string-append name "-" version ".tar.gz"))
+       (sha256
+        (base32
+         "0dpcddizs4zhbvbsv3kxx9p0qppidxh05jz7dlf45f5rsm9pbfrs"))
+       (modules '((guix build utils)))
+       (snippet
+        '(begin
+           ;; Allow older versions of the serde crates.
+           (substitute* "Cargo.toml"
+             (("1.0.136") "1.0.133")
+             (("1.0.79") "1.0.74"))))))
+    (build-system cargo-build-system)
+    (arguments
+     `(#:tests? #f              ; Not all tests included.
+       #:cargo-inputs
+       (("rust-camino" ,rust-camino-1)
+        ("rust-cargo-platform" ,rust-cargo-platform-0.1)
+        ("rust-derive-builder" ,rust-derive-builder-0.11)
+        ("rust-semver" ,rust-semver-1)
+        ("rust-serde" ,rust-serde-1)
+        ("rust-serde-json" ,rust-serde-json-1))))
+    (home-page "https://github.com/oli-obk/cargo_metadata")
+    (synopsis "Structured access to the output of `cargo metadata`")
+    (description
+     "This package provides structured access to the output of @code{cargo
+metadata}.")
+    (license license:expat)))
+
 (define-public rust-cargo-metadata-0.14
   (package
+    (inherit rust-cargo-metadata-0.15)
     (name "rust-cargo-metadata")
     (version "0.14.1")
     (source
@@ -9357,7 +9395,6 @@ the library crate of Cargo.")
        (sha256
         (base32
          "04kfzvmh80pq0bw1cwzlz71wfrign2k7792mc4gi8hs1jkgfcams"))))
-    (build-system cargo-build-system)
     (arguments
      `(#:skip-build? #t
        #:cargo-inputs
@@ -9366,13 +9403,7 @@ the library crate of Cargo.")
         ("rust-derive-builder" ,rust-derive-builder-0.9)
         ("rust-semver" ,rust-semver-1)
         ("rust-serde" ,rust-serde-1)
-        ("rust-serde-json" ,rust-serde-json-1))))
+        ("rust-serde-json" ,rust-serde-json-1))))))
-    (home-page "https://github.com/oli-obk/cargo_metadata")
-    (synopsis "Structured access to the output of `cargo metadata`")
-    (description
-     "This package provides structured access to the output of @code{cargo
-metadata}.")
-    (license license:expat)))
 
 (define-public rust-cargo-metadata-0.13
   (package