paco pkg: allow a commit id to be used in a GitHub reference

Allow a commit id in place of a branch or tag.

pkgs/racket-pkgs/racket-doc/pkg/scribblings/pkg.scrbl

@@ -189,11 +189,11 @@ URLs is:
 
 @inset{@exec{git://github.com/}@nonterm{user}@exec{/}@nonterm{repo}@;
 @optional{@exec{.git}}@optional{@exec{/}}@optional{@exec{?path=}@nonterm{path}}@;
-@optional{@exec{#}@nonterm{tag}}}
+@optional{@exec{#}@nonterm{rev}}}
 
 where @nonterm{path} can contain multiple @litchar{/}-separated
 elements to form a path within the repository, and defaults to the
-empty path. The @nonterm{tag} can be a branch or tag, and it
+empty path. The @nonterm{rev} can be a branch, tag, or commit, and it
 defaults to @exec{master}.
 
 For example, @filepath{git://github.com/game/tic-tac-toe#master}
@@ -202,12 +202,13 @@ is a GitHub package source.
 For backward compatibility, an older format is also supported:
 
 @inset{@exec{github://github.com/}@nonterm{user}@exec{/}@nonterm{repo}@;
-@exec{/}@nonterm{tag}@optional{@exec{/}@nonterm{path}}}
+@exec{/}@nonterm{rev}@optional{@exec{/}@nonterm{path}}}
 
 The @exec{zip}-formatted archive for the repository (generated by
-GitHub for every branch and tag) is used as a remote URL archive path,
-except the @tech{checksum} is the hash identifying the branch (or
-tag).
+GitHub for any commit) is used as a remote URL archive path.  The
+@tech{checksum} is the hash identifying @nonterm{rev} if @nonterm{rev}
+is a branch or tag, otherwise @nonterm{rev} itself serves as the
+@tech{checksum}.
 
 A package source is inferred to be a GitHub reference when it
 starts with @litchar{git://} or @litchar{github://}; a package source that is otherwise

pkgs/racket-pkgs/racket-test/tests/pkg/tests-network.rkt

@@ -30,6 +30,10 @@
    "remote/github with tag"
    "git://github.com/mflatt/pkg-test?path=pkg-test1/#hundred"
    $ "racket -l racket/base -l pkg-test1/number -e '(number)'" =stdout> "100\n")
+  (shelly-install 
+   "remote/github with commit"
+   "git://github.com/mflatt/pkg-test?path=pkg-test1/#f9b4eef22"
+   $ "racket -l racket/base -l pkg-test1/number -e '(number)'" =stdout> "100\n")
   (shelly-install 
    "remote/github with checksum"
    "--checksum f9b4eef22cdd9ab88b254cb027fc1ebe7fb596fd git://github.com/mflatt/pkg-test?path=pkg-test1"

racket/collects/pkg/util.rkt

@@ -76,6 +76,7 @@
     [(or "github" "git")
      (match-define (list* user repo branch path)
                    (split-github-url pkg-url))
+     (or
       (for/or ([kind '("branches" "tags")])
         (define api-u
           (url "https" #f "api.github.com" #f #t
@@ -109,7 +110,11 @@
                  api-bs))
         (for/or ([b (in-list branches)])
           (and (equal? (hash-ref b 'name) branch)
-              (hash-ref (hash-ref b 'commit) 'sha))))]
+               (hash-ref (hash-ref b 'commit) 'sha))))
+      ;; no matching branch/tag found, so if `branch' matches the
+      ;; syntax of a commit id, then assume that it refers to a commit
+      (and (regexp-match? #rx"[a-f0-9]+" branch)
+           branch))]
     [_
      (define u (string-append pkg-url-str ".CHECKSUM"))
      (download-printf "Downloading checksum for ~a\n" pkg-name)