Skip mirror if the URL is cache.ruby-lang.org (Fastly) and there's no custom mirror set

bin/ruby-build

@@ -327,7 +327,9 @@ fetch_tarball() {
     package_url="${package_url%%#*}"
 
     if [ -n "$RUBY_BUILD_MIRROR_URL" ]; then
-      mirror_url="${RUBY_BUILD_MIRROR_URL}/$checksum"
+      if [[ -z "$RUBY_BUILD_DEFAULT_MIRROR" || $package_url != */cache.ruby-lang.org/* ]]; then
+        mirror_url="${RUBY_BUILD_MIRROR_URL}/$checksum"
+      fi
     fi
   fi
 
@@ -1190,8 +1192,10 @@ fi
 
 if [ -z "$RUBY_BUILD_MIRROR_URL" ]; then
   RUBY_BUILD_MIRROR_URL="https://dqw8nmjcqpjn7.cloudfront.net"
+  RUBY_BUILD_DEFAULT_MIRROR=1
 else
   RUBY_BUILD_MIRROR_URL="${RUBY_BUILD_MIRROR_URL%/}"
+  RUBY_BUILD_DEFAULT_MIRROR=
 fi
 
 if [ -n "$RUBY_BUILD_SKIP_MIRROR" ]; then

test/mirror.bats

@@ -101,3 +101,21 @@ export RUBY_BUILD_MIRROR_URL=http://mirror.example.com
   unstub curl
   unstub shasum
 }
+
+
+@test "package URL with ruby-lang CDN with default mirror URL will bypasses mirror" {
+  export RUBY_BUILD_MIRROR_URL=
+  local checksum="ba988b1bb4250dee0b9dd3d4d722f9c64b2bacfc805d1b6eba7426bda72dd3c5"
+
+  stub shasum true "echo $checksum"
+  stub curl "-q -o * -*S* https://cache.ruby-lang.org/* : cp $FIXTURE_ROOT/\${5##*/} \$3"
+
+  run_inline_definition <<DEF
+install_package "package-1.0.0" "https://cache.ruby-lang.org/packages/package-1.0.0.tar.gz#ba988b1bb4250dee0b9dd3d4d722f9c64b2bacfc805d1b6eba7426bda72dd3c5" copy
+DEF
+  assert_success
+  assert [ -x "${INSTALL_ROOT}/bin/package" ]
+
+  unstub curl
+  unstub shasum
+}