Improve support for selecting and downloading changes

This change adds support for selecting and downloading changes that
match a custom gerrit query (e.g. "is:open").

A new interactive function called `gerrit-download-and-open-overview'
was added which downloads the change and opens an magit-commit buffer
using `magit-show-commit'. (It the downloaded change is at the top of a
relation chain, the other commits are currently not displayed by this
`gerrit-download-and-open-overview' function.

Closes: #19
Change-Id: Ie3ed04a8f212cb8c0a98745d1dca4f680f420642

gerrit.el

@@ -148,13 +148,42 @@ gerrit-download is used."
 ;; -> The test-transient allows one to cycle over all settings C-M-p / C-M-n
 ;; and also over all the infix history
 
+;; this variable is used in `gerrit-download-format-change'
+(defvar gerrit-change-singleline-columns
+  '(number branch subject)
+  "List of columns that should be displayed in functions that ask the user to select a change from a list of changes."
+  "Currently supported columns are:"
+  "'number (the change number)"
+  "'branch (the branch of the change)"
+  "'subject (the subject of the commit msg)"
+  "'project (the project name)"
+  )
+
+;; TODO document this variable
+;; (setq gerrit-project-to-local-workspace-alist
+;;   '(
+;;     (("software/pro1" . "branch1") . "~/sandbox/pro1")
+;;     (("software/pro2" . "branch2") . "~/sandbox/pro2")
+;;   ))
+(defvar gerrit-project-to-local-workspace-alist nil)
+
+;; TODO docs missing
+;; mention (project:A OR project:B OR project:C)
+(defvar gerrit-interesting-open-changes-filter "is:open")
+
 (defun gerrit-download-format-change (change)
-  (concat
-   (propertize (number-to-string (alist-get '_number change)) 'face 'magit-hash)
-   " "
-   (propertize (alist-get 'branch change) 'face 'magit-branch-remote)
-   " "
-   (propertize (alist-get 'subject change) 'face 'magit-section-highlight)))
+  (let (columns)
+    ;; can this be implemented in an easier way?
+    (when (member 'number gerrit-change-singleline-columns)
+      (add-to-list 'columns (propertize (number-to-string
+                         (alist-get '_number change)) 'face 'magit-hash)))
+    (when (member 'project gerrit-change-singleline-columns)
+      (add-to-list 'columns (propertize (alist-get 'project change) 'face 'magit-branch-remote)))
+    (when (member 'branch gerrit-change-singleline-columns)
+      (add-to-list 'columns (propertize (alist-get 'branch change) 'face 'magit-branch-remote)))
+    (when (member 'subject gerrit-change-singleline-columns)
+      (add-to-list 'columns (propertize (alist-get 'subject change) 'face 'magit-section-highlight)))
+    (s-join " " (nreverse columns))))
 
 (defun gerrit-download--get-refspec (change-metadata)
   "Return the refspec of a gerrit change from CHANGE-METADATA.
@@ -198,6 +227,7 @@ This refspec is a string of the form 'refs/changes/xx/xx/x'.
     ;; (e.g. if ssh-add was not called) this async call runs
     ;; magit-process-password-prompt-regexps (used in magit-process-filter)
     ;; which is called in magit-start-process
+    ;; (see https://github.com/magit/magit/issues/4323)
     (magit-run-git-async "fetch"
                          (gerrit-get-remote)
                          (gerrit-download--get-refspec change-metadata))
@@ -1196,25 +1226,62 @@ gerrit-upload: (current cmd: %(concat (gerrit-upload-create-git-review-cmd)))
 
 
 
+(defun gerrit--select-change-from-matching-changes (search-string)
+  ;; see https://gerrit-review.googlesource.com/Documentation/user-search.html
+  ;; clients can let-bind `gerrit-change-singleline-columns'
+  (let* ((open-changes (seq-map #'reviewgerrit-download-format-change
+                                (gerrit-rest-change-query
+                                 (or search-string "is:open")
+                                 )))
+         (selected-line (completing-read
+                         "Download Change: " open-changes nil nil))
+         (changenr (car (s-split " " (s-trim selected-line)))))
+    changenr))
+
 (defun gerrit-download (changenr)
   "Download change with CHANGENR from the gerrit server."
   (interactive
    (list
-    (let* ((open-changes
-            (seq-map #'gerrit-download-format-change (gerrit-rest-change-query
-                                                      (concat "status:open project:"
-                                                              (gerrit-get-current-project)))))
-           (selected-line (completing-read
-                           "Download Change: " open-changes nil nil))
-           (changenr (car (s-split " " (s-trim selected-line)))))
-      changenr
-      )))
+    (let
+        ((gerrit-change-singleline-columns '(number branch project subject)))
+      (gerrit--select-change-from-matching-changes
+       (concat "status:open project:"
+               (gerrit-get-current-project))))))
 
   (gerrit--init-accounts)
   (if gerrit-use-gitreview-interface
       (gerrit-download--gitreview changenr)
     (gerrit-download--new changenr)))
 
+;; TODO split this up into two parts (one that downloads the change and one that opens the overview page using magit-show-commit
+(defun gerrit-download-and-open-overview (changenr)
+  ;; since a simple "is:open" query might return a lot of gerrit-changes, it
+  ;; is possible to filter the returned results by setting an variable
+  ;; called `gerrit-interesting-open-changes-filter'.
+  (interactive (list (gerrit--select-change-from-matching-changes
+                      gerrit-interesting-open-changes-filter)))
+
+  ;; 1) get change metadata
+  ;; 2) determine workspace directory (based on branch and projectname)
+  ;; 3) switch to workspace
+  ;; 4) download change
+  ;; 5) display commit
+  (let* ((change-metadata (car (gerrit-rest-change-query changenr)))
+         (project-name (alist-get 'project change-metadata))
+         (branch (alist-get 'branch change-metadata))
+         (workspace-directory (or (cdr (assoc (cons project-name branch)
+                                              gerrit-project-to-local-workspace-alist))
+                                  ;; TODO completion + write them to file
+                                  (read-directory-name
+                                   (format "Enter directory for project %s" project-name)))))
+    (let ((default-directory workspace-directory))
+      (message "changeinfo: name: %s, branch: %s -> workspace: %s"
+               project-name branch workspace-directory)
+      (gerrit-download changenr) ;; this is async
+      ;; TODO run magit-show-commit
+      ;; only when the above change is downloaded to avoid window-flickering
+      (magit-show-commit "HEAD"))))
+
 (defun gerrit-upload ()
   (interactive)
    (if gerrit-use-gitreview-interface