new version with git help

main.rkt

@@ -9,12 +9,16 @@
          racket/match
          racket/path
          racket/string
+         net/sendurl
+         setup/xref
+         scribble/xref
          "credentials.rkt"
          libgit2)
 
 (provide git
          dgit
          git-version
+         git-help
          git-repository?
          git-root
          git-init
@@ -80,6 +84,63 @@
     (error 'git-version "cannot read info.rkt"))
   (info 'version (lambda () (error 'git-version "info.rkt has no version"))))
 
+(define git-help-bindings
+  (hash 'version 'git-version
+        'init 'git-init
+        'clone 'git-clone
+        'status 'git-status
+        'diff 'git-diff
+        'add 'git-add
+        'restore 'git-restore
+        'reset 'git-reset
+        'grep 'git-grep
+        'config 'git-config
+        'commit 'git-commit
+        'branch-current 'git-current-branch
+        'branch 'git-branch
+        'branch-create 'git-branch-create
+        'switch 'git-switch
+        'checkout 'git-checkout
+        'merge 'git-merge
+        'tag 'git-tag
+        'log 'git-log
+        'remote 'git-remotes
+        'fetch 'git-fetch
+        'pull 'git-pull
+        'push 'git-push
+        'push-tag 'git-push-tag
+        'credentials 'git-credentials-init!
+        'prompt 'git-prompt
+        'git-prompt 'git-prompt
+        'help 'git-help))
+
+(define (git-help [topic #f])
+  (unless (or (not topic) (symbol? topic))
+    (raise-argument-error 'git-help "(or/c #f symbol?)" topic))
+  (define binding
+    (if topic
+        (hash-ref git-help-bindings topic
+                  (lambda ()
+                    (error 'git-help "unknown help topic: ~a" topic)))
+        'git))
+  ;; Use Racket's installed-documentation cross-reference database instead of
+  ;; guessing where raco setup placed this package's generated HTML.
+  (define xref (load-collections-xref))
+  (define tag
+    (xref-binding->definition-tag xref (list 'git binding) #f))
+  (unless tag
+    (error 'git-help
+           "documentation for ~a is not indexed; run raco setup git"
+           binding))
+  (define-values (path anchor)
+    (xref-tag->path+anchor xref tag))
+  (unless path
+    (error 'git-help
+           "documentation for ~a is indexed but has no local path"
+           binding))
+  (send-url/file path #:fragment anchor)
+  (void))
+
 (define zero-oid-string (make-string GIT_OID_HEXSZ #\0))
 (define branch-prefix "refs/heads/")
 (define tag-prefix "refs/tags/")
@@ -1170,6 +1231,11 @@
      (unless (null? args)
        (error 'git "version takes no arguments"))
      (git-version)]
+    [(help)
+     (match args
+       ['() (git-help)]
+       [(list topic) (git-help topic)]
+       [_ (error 'git "help takes zero or one topic")])]
     [(init) (apply git-init args)]
     [(clone) (keyword-apply git-clone '(#:quiet) (list quiet) args)]
     [(status) (apply git-status args)]