Use SPDX license identifiers for license in shard.yml

docs/shard.yml.adoc

@@ -204,8 +204,14 @@ libraries:
 ----
 
 *license*::
-  An http://opensource.org/[OSI license] name or an URL to a license file
-(string, recommended).
+An https://spdx.github.io/spdx-spec/v3.0.1/annexes/spdx-license-expressions/[SPDX license expression]
+or an URL to a license file (string, recommended).
++
+The OSI publishes https://opensource.org/licenses-old/category[a list] of open
+source licenses and their corresponding SPDX identifiers.
++
+Examples: _Apache-2.0_, _GPL-3.0-or-later_, _Apache-2.0 OR MIT_,
+_Apache-2.0 WITH Swift-exception_, _https://example.com/LICENSE_.
 
 *repository*::
 The URL of the project's canonical repository (string, recommended).

docs/shard.yml.schema.json

@@ -222,7 +222,7 @@
     "license": {
       "type": "string",
       "title": "license",
-      "description": "An OSI license name or an URL to a license file"
+      "description": "An SPDX license expression or an URL to a license file."
     },
     "repository": {
       "type": "string",

spec/unit/spec_spec.cr

@@ -29,7 +29,7 @@ module Shards
     it "parse license" do
       spec = Spec.from_yaml("name: shards\nversion: 0.1.0\nlicense: BSD-2-Clause")
       spec.license.should eq("BSD-2-Clause")
-      spec.license_url.should eq("http://opensource.org/licenses/BSD-2-Clause")
+      spec.license_url.should eq("https://spdx.org/licenses/BSD-2-Clause")
 
       spec = Spec.from_yaml("name: shards\nversion: 0.1.0\nlicense: http://example.com/LICENSE")
       spec.license.should eq("http://example.com/LICENSE")

src/spec.cr

@@ -218,7 +218,7 @@ module Shards
         if license =~ %r(https?://)
           license
         else
-          "http://opensource.org/licenses/#{license}"
+          "https://spdx.org/licenses/#{license}"
         end
       end
     end