change Git package references to use default branch

If a Git package source does not include "#" followed by a ref, then
use the branch/commit designated by a server as the default branch or
commit (i.e., the one for the "HEAD" symref), instead of assuming the
branch "master".

This is technically a backward-incompatible change to the
interpretation of Git package sources, but explicit branch
specification continues to work the same. For the forseeable future,
to support recent versions, packages in a branch other than "master"
will still need to be specified using the branch name, such as
including "#main" at the end of the package source. Eventually,
relevant versions of Racket will support the new default.

Relevant to #3672

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

@@ -383,8 +383,8 @@ is:
 
 @inset{@exec{https://github.com/@nonterm{user}/@nonterm{package}.git}}
 
-If you want the package to be @nonterm{branch} or @nonterm{tag}
+If you want the package to be at @nonterm{branch} or @nonterm{tag}
-instead of @exec{master}, then add @filepath{#@nonterm{branch}} or
+instead of the default branch, then add @filepath{#@nonterm{branch}} or
 @filepath{#@nonterm{tag}} to the end of the package source. If your
 package is a subdirectory @nonterm{path} within the repository, add
 @filepath{?path=@nonterm{path}} to the end of the package source.

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

@@ -120,7 +120,7 @@ develops only a few of them. The intended workflow is as follows:
   repository by setting an @exec{upstream} remote, e.g. @exec{git
   remote add upstream @nonterm{url-of-central-repo}}. This gives you
   the option to periodically pull in commits from the central
-  repository with @exec{git pull --ff-only upstream master}.}
+  repository with @exec{git pull --ff-only upstream}.}
 
   Alternatively, use @exec{git} to clone the target @nonterm{url}
   first, and then supply the local clone's path as @nonterm{dir} in

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

@@ -249,14 +249,15 @@ where @nonterm{scheme} is @litchar{git}, @litchar{http}, or
 reference). The @nonterm{path} can contain multiple
 @litchar{/}-separated elements to form a path within the repository,
 and it defaults to the empty path. The @nonterm{rev} can be a branch,
-tag, or commit, and it defaults to @exec{master}.
+tag, or commit, and it defaults to using the default branch as reported
+by the server.
 
 @margin-note{Due to properties of the Git protocol, the archive might
 be accessed more efficiently when @nonterm{rev} refers to a branch or
 tag (even if it is written as a commit). In those cases, the content
 typically can be obtained without downloading irrelevant history.}
 
-For example, @filepath{http://bitbucket.org/game/tic-tac-toe#master}
+For example, @filepath{http://bitbucket.org/game/tic-tac-toe#main}
 is a Git package source. 
 
 A checkout of the repository at @nonterm{rev} provides the content of
@@ -285,7 +286,7 @@ URLs is the same as for a Git repository reference starting
 @optional{@exec{.git}}@optional{@exec{/}}@optional{@exec{?path=}@nonterm{path}}@;
 @optional{@exec{#}@nonterm{rev}}}
 
-For example, @filepath{git://github.com/game/tic-tac-toe#master}
+For example, @filepath{git://github.com/game/tic-tac-toe#main}
 is a GitHub package source.
 
 @margin-note{A Github repository source that starts with

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

@@ -53,8 +53,8 @@
          $ "raco pkg remove pkg-test1-git-different-checksum"
          $ "racket -l pkg-test1/number" =exit> 1))))
 
- (test-remote "git://github.com/mflatt/pkg-test")
+ (test-remote "git://github.com/racket/test-pkg-1")
- (test-remote "https://github.com/mflatt/pkg-test.git")
+ (test-remote "https://github.com/racket/test-pkg-1.git")
  (test-remote "https://bitbucket.org/mflatt/pkg-test.git")
 
  (define (try-git-repo label type+repo)
@@ -69,10 +69,26 @@
      $ (~a "raco pkg update " type+repo)
      (finally
       (delete-directory/files tmp-dir)))))
- 
+
  (try-git-repo
   "remote/github with auto prefix and with branch"
-  "--type github mflatt/pkg-test?path=pkg-test1/#alt")
+  "--type github racket/test-pkg-1?path=pkg-test1/#alt")
  (try-git-repo
   "remote/git type"
-  "--type git https://bitbucket.org/mflatt/pkg-test?path=pkg-test1#alt"))
+  "--type git https://bitbucket.org/mflatt/pkg-test?path=pkg-test1#alt")
+
+ (define (try-git-repo-using-default-branch label repo)
+   (define tmp-dir (make-temporary-file "~a-clone" 'directory))
+   (shelly-wind
+    $ (~a "raco pkg install " repo)
+    $ "racket -l test-pkg-2/twelve" =stdout> "12\n"
+    $ (~a "raco pkg update --clone " tmp-dir " test-pkg-2")
+    $ "racket -l test-pkg-2/twelve" =stdout> "12\n"
+    $ (~a "raco pkg update " repo)
+    $ "raco pkg remove " repo
+    (finally
+     (delete-directory/files tmp-dir))))
+
+ (try-git-repo-using-default-branch
+  "remote/git with default branch"
+  "https://github.com/racket/test-pkg-2.git"))

racket/collects/pkg/private/repo-path.rkt

@@ -41,7 +41,7 @@
           (string-join (map (compose ~a path/param-path)
                             (url-path/no-slash pkg-url))
                        "/")
-          (or (url-fragment pkg-url) "master")
+          (or (url-fragment pkg-url) 'head)
           (extract-git-path pkg-url)))
 
 (define (split-git-or-hub-url pkg-url #:type [type #f])

racket/collects/pkg/private/stage.rkt

@@ -206,13 +206,19 @@
                           clone-dir)
          (make-directory* clone-dir)
          (parameterize ([current-directory clone-dir])
-           (git #:status status "clone" "-b" branch pkg-no-query ".")))
+           (apply git #:status status "clone"
+                  (append
+                   (if (eq? branch 'head) null (list "-b" branch))
+                   (list pkg-no-query ".")))))
 
        (unless working-dir
          (parameterize ([current-directory clone-dir])
            (download-printf "Fetching from remote repository ~a\n"
                             pkg-no-query)
-           (git #:status status "fetch" pkg-no-query branch)))
+           (apply git #:status status "fetch"
+                  (append
+                   (list pkg-no-query)
+                   (if (eq? branch 'head) null (list branch))))))
 
        (cond
         [tmp-dir
@@ -225,7 +231,11 @@
          (download-printf "Cloning repository locally for staging\n")
          (git #:status status "clone" "--shared" clone-dir tmp-dir)
          (parameterize ([current-directory tmp-dir])
-           (git #:status status "checkout" (or checksum branch)))
+           (apply git #:status status "checkout"
+                  (cond
+                    [checksum => list]
+                    [(eq? branch 'head) null]
+                    [else (list branch)])))
          (lift-git-directory-content tmp-dir path)]
         [else
          (download-printf "Using clone directory directly for metadata\n")])
@@ -771,43 +781,49 @@
                              (current-continuation-marks))))
                          #:transport transport)))))]
     [(github)
-     (match-define (list* user repo branch path)
+     (match-define (list* user repo url-branch path)
-                   (split-github-url pkg-url))
+       (split-github-url pkg-url))
+     (define (query-json path kind)
+       (define api-u
+         (url "https" #f "api.github.com" #f #t
+              (map (λ (x) (path/param x empty))
+                   path)
+              (append query
+                      (if (and (github-client_id)
+                               (github-client_secret))
+                          (list (cons 'client_id (github-client_id))
+                                (cons 'client_secret (github-client_secret)))
+                          empty))
+              #f))
+       (download-printf "Querying GitHub ~a for ~a\n" kind pkg-name)
+       (log-pkg-debug "Querying GitHub at ~a" (url->string api-u))
+       (define api-bs
+         (call/input-url+200
+          api-u port->bytes
+          #:who 'query-github
+          #:headers (list (format "User-Agent: raco-pkg/~a" (version)))))
+       (unless api-bs
+         (error 'package-url->checksum
+                "could not connect to GitHub\n URL: ~a"
+                (url->string 
+                 (struct-copy url api-u
+                              [query query]))))
+       (read-json (open-input-bytes api-bs)))
+     (define branch (cond
+                      [(eq? url-branch 'head)
+                       (define info (query-json (list "repos" user repo) 'head))
+                       (hash-ref info 'default_branch)]
+         [else url-branch]))
      (or
       (for/or ([kind '("branches" "tags")])
-        (define api-u
+        (define branches (query-json (list "repos" user repo kind) kind))
-          (url "https" #f "api.github.com" #f #t
-               (map (λ (x) (path/param x empty))
-                    (list "repos" user repo kind))
-               (append query
-                       (if (and (github-client_id)
-                                (github-client_secret))
-                           (list (cons 'client_id (github-client_id))
-                                 (cons 'client_secret (github-client_secret)))
-                           empty))
-               #f))
-        (download-printf "Querying GitHub ~a for ~a\n" kind pkg-name)
-        (log-pkg-debug "Querying GitHub at ~a" (url->string api-u))
-        (define api-bs
-          (call/input-url+200
-           api-u port->bytes
-           #:who 'query-github
-           #:headers (list (format "User-Agent: raco-pkg/~a" (version)))))
-        (unless api-bs
-          (error 'package-url->checksum
-                 "could not connect to GitHub\n URL: ~a"
-                 (url->string 
-                  (struct-copy url api-u
-                               [query query]))))
-        (define branches
-          (read-json (open-input-bytes api-bs)))
         (unless (and (list? branches)
                      (andmap hash? branches)
                      (andmap (λ (b) (hash-has-key? b 'name)) branches)
                      (andmap (λ (b) (hash-has-key? b 'commit)) branches))
           (error 'package-url->checksum
                  "Invalid response from Github: ~e"
-                 api-bs))
+                 branches))
         (for/or ([b (in-list branches)])
           (and (equal? (hash-ref b 'name) branch)
                (hash-ref (hash-ref b 'commit) 'sha))))