add --null switch to `raco pollen render` (closes #24)

pollen/private/command.rkt

@@ -98,7 +98,7 @@ version                print the version" (current-server-port) (make-publish-di
   (define render-target-wanted (make-parameter (current-poly-target)))
   (define render-with-subdirs? (make-parameter #f))
   (define render-parallel? (make-parameter #f))
-  (define dry-run? (make-parameter #f))
+  (define special-output? (make-parameter #f))
   (define parsed-args
     (command-line #:program "raco pollen render"
                   #:argv (vector-drop (current-command-line-arguments) 1) ; snip the 'render' from the front
@@ -108,7 +108,9 @@ version                print the version" (current-server-port) (make-publish-di
                   [("-r" "--recursive") "Render subdirectories recursively"
                                         (render-with-subdirs? 'recursive)]
                   [("-s" "--subdir") "Render subdirectories nonrecursively" (render-with-subdirs? 'include)]
-                  [("-d" "--dry-run") "Print paths that would be rendered" (dry-run? #true)]
+                  #:once-any
+                  [("-d" "--dry-run") "Print paths that would be rendered" (special-output? 'dry-run)]
+                  [("-n" "--null") "Suppress file output" (special-output? 'null)]
                   #:once-any
                   [("-p" "--parallel") "Render in parallel using all cores" (render-parallel? #true)]
                   [("-j" "--jobs") job-count "Render in parallel using <job-count> jobs" (render-parallel? (or (string->number job-count) (raise-argument-error 'handle-render "exact positive integer" job-count)))]
@@ -116,7 +118,7 @@ version                print the version" (current-server-port) (make-publish-di
                   other-args))
 
   (define (handle-batch-render paths)
-    (apply render-batch (map very-nice-path paths) #:parallel (render-parallel?) #:dry-run (dry-run?)))
+    (apply render-batch (map very-nice-path paths) #:parallel (render-parallel?) #:special (special-output?)))
   
   (parameterize ([current-poly-target (render-target-wanted)]) ;; applies to both cases
     (let loop ([args parsed-args])

pollen/private/ts.rktd

@@ -1 +1 @@
-1575833252
+1576204032

pollen/render.rkt

@@ -155,9 +155,11 @@
          [(list wpidx wp 'wants-lock path)
           (loop source-paths locks (append blocks (list (cons wp path))) completed-jobs completed-job-count)])])))
 
+(define current-null-output? (make-parameter #f))
+
 (define+provide/contract (render-batch #:parallel [wants-parallel-render? #false]
-                                       #:dry-run [wants-dry-run? #false] . paths-in)
-  ((#:parallel any/c) (#:dry-run boolean?) #:rest (listof pathish?) . ->* . void?)
+                                       #:special [special-output #false] . paths-in)
+  ((#:parallel any/c) (#:special (or/c boolean? symbol?)) #:rest (listof pathish?) . ->* . void?)
   ;; Why not just (for-each render ...)?
   ;; Because certain files will pass through multiple times (e.g., templates)
   ;; And with render, they would be rendered repeatedly.
@@ -176,12 +178,13 @@
            [_ (loop rest acc)])])))
   (cond
     [(null? expanded-source-paths) (message "[no paths to render]")]
-    [wants-dry-run? (for-each message expanded-source-paths)]
-    [else (for-each render-to-file-if-needed
-                    (match wants-parallel-render?
-                      ;; returns crashed jobs for serial rendering
-                      [#false expanded-source-paths]
-                      [jobs-arg (parallel-render expanded-source-paths jobs-arg)]))]))
+    [(eq? special-output 'dry-run) (for-each message expanded-source-paths)]
+    [else (parameterize ([current-null-output? (eq? special-output 'null)])
+            (for-each render-to-file-if-needed
+                      (match wants-parallel-render?
+                        ;; returns crashed jobs for serial rendering
+                        [#false expanded-source-paths]
+                        [jobs-arg (parallel-render expanded-source-paths jobs-arg)])))]))
 
 (define (pagetree->paths pagetree-or-path)    
   (parameterize ([current-directory (current-project-root)])
@@ -246,10 +249,11 @@
                                   (message (format "from cache /~a"
                                                    (find-relative-path (current-project-root) output-path))))))]
         [else (render-thunk)]))
-    (display-to-file render-result
-                     output-path
-                     #:exists 'replace
-                     #:mode (if (string? render-result) 'text 'binary))))
+    (unless (current-null-output?)
+      (display-to-file render-result
+                       output-path
+                       #:exists 'replace
+                       #:mode (if (string? render-result) 'text 'binary)))))
 
 (define+provide/contract (render-to-file-if-needed source-path [maybe-template-path #f] [maybe-output-path #f] [maybe-render-thunk #f])
   ((complete-path?) ((or/c #f complete-path?) (or/c #f complete-path?) (or/c #f procedure?)) . ->* . void?)

pollen/scribblings/raco.scrbl

@@ -76,7 +76,10 @@ Adding the optional @exec{--local} switch will restrict the project server to re
 
 This command can be invoked two ways: in source mode or directory mode.
 
-In both modes, the optional @exec{--dry-run} or @exec{-d} switch prints the paths that would be rendered by this command without actually doing so.
+In both modes, the optional @exec{--dry-run} or @exec{-d} switch prints the paths that would be rendered by this command without actually doing so. 
+
+In both modes, the optional @exec{--null} or @exec{-n} switch renders as usual, but doesn't write any files. (Convenient if you're arranging special render behavior, for instance writing to a database or network server.)
+
 
 
 @bold{Source mode}: @racket[raco pollen render _source ...] will render only the source paths specified in @racket[_source ...]. Consistent with the usual command-line idiom, this can be a single path, a list of paths, or a pattern: