import: crate: Use existing package satisfying semver requirement.

If a package satisfying the dependency's semver requirement already exists,
use it. Prior to this change the highest version matching the semver
requirement was used (and imported in case it was not defined as package
already).

When resolving a dependency (now done in `sort-map-dependencies`), first
search for a package matching the semver requirement and only if this fails
reach out for a crate.

* guix/import/crate.scm (crate->guix-package)[find-package-version]: New
  function. [dependency-name+version]: New function.
  [sort-map-dependencies]: Use it instead of lambda function.

* tests/crate.scm (test-doctool-crate, test-doctool-dependencies): New
  variables.
  ("self-test …", "cargo-recursive-import-hoors-existing-packages"): New
  tests.

tests/crate.scm

@@ -25,6 +25,7 @@
   #:use-module (guix build-system cargo)
   #:use-module (gcrypt hash)
   #:use-module (guix tests)
+  #:use-module (gnu packages)
   #:use-module (ice-9 iconv)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-64))
@@ -312,6 +313,7 @@
   \"dependencies\": []
 }")
 
+
 (define test-source-hash
   "")
 
@@ -572,4 +574,85 @@
   '(license:expat license:asl2.0)
   (string->license "MIT/Apache-2.0"))
 
+
+
+(define test-doctool-crate
+  "{
+  \"crate\": {
+    \"max_version\": \"2.2.2\",
+    \"name\": \"leaf-bob\",
+    \"description\": \"summary\",
+    \"homepage\": \"http://example.com\",
+    \"repository\": \"http://example.com\",
+    \"keywords\": [\"dummy\", \"test\"],
+    \"categories\": [\"test\"]
+    \"actual_versions\": [
+      { \"id\": 234280,
+        \"num\": \"2.2.2\",
+        \"license\": \"MIT OR Apache-2.0\",
+        \"links\": {
+          \"dependencies\": \"/api/v1/crates/doctool/2.2.2/dependencies\"
+        }
+      }
+    ]
+  }
+}")
+
+;; FIXME: This test depends on some existing packages
+(define test-doctool-dependencies
+  "{
+  \"dependencies\": [
+     {
+       \"crate_id\": \"docopt\",
+       \"kind\": \"normal\",
+       \"req\": \"^0.8.1\"
+     }
+  ]
+}")
+
+
+(test-assert "self-test: rust-docopt 0.8.x is gone, please adjust the test case"
+  (not (null? (find-packages-by-name "rust-docopt" "0.8"))))
+
+(test-assert "cargo-recursive-import-hoors-existing-packages"
+  (mock ((guix http-client) http-fetch
+         (lambda (url . rest)
+           (match url
+             ("https://crates.io/api/v1/crates/doctool"
+              (open-input-string test-doctool-crate))
+             ("https://crates.io/api/v1/crates/doctool/2.2.2/download"
+              (set! test-source-hash
+                    (bytevector->nix-base32-string
+                     (sha256 (string->bytevector "empty file\n" "utf-8"))))
+              (open-input-string "empty file\n"))
+             ("https://crates.io/api/v1/crates/doctool/2.2.2/dependencies"
+              (open-input-string test-doctool-dependencies))
+             (_ (error "Unexpected URL: " url)))))
+        (match (crate-recursive-import "doctool")
+          (((define-public 'rust-doctool-2
+              (package
+                (name "rust-doctool")
+                (version "2.2.2")
+                (source
+                 (origin
+                   (method url-fetch)
+                   (uri (crate-uri "doctool" version))
+                   (file-name
+                    (string-append name "-" version ".tar.gz"))
+                   (sha256
+                    (base32
+                     (?  string? hash)))))
+                (build-system cargo-build-system)
+                (arguments
+                 ('quasiquote (#:cargo-inputs
+                               (("rust-docopt"
+                                 ('unquote 'rust-docopt-0.8))))))
+                (home-page "http://example.com")
+                (synopsis "summary")
+                (description "summary")
+                (license (list license:expat license:asl2.0)))))
+            #t)
+          (x
+           (pk 'fail x #f)))))
+
 (test-end "crate")