[RFC] Allow dune to treat targets opaquely.

CHANGES.md

@@ -28,6 +28,10 @@ next
 - Fix `dune build @doc` deleting `highlight.pack.js` on rebuilds, after the
   first build (#1557, @aantron).
 
+- Allow targets to be directories, which Dune will treat opaquely
+  (#1547, @jordwalke)
+
+
 1.5.1 (7/11/2018)
 -----------------
 

src/build_system.ml

@@ -705,21 +705,21 @@ let remove_old_artifacts t ~dir ~subdirs_to_keep =
     | files ->
       List.iter files ~f:(fun fn ->
         let path = Path.relative dir fn in
-        match Unix.lstat (Path.to_string path) with
-        | { st_kind = S_DIR; _ } -> begin
-            match subdirs_to_keep with
-            | All -> ()
-            | These set ->
-              if String.Set.mem set fn ||
-                 Path.Set.mem t.build_dirs_to_keep path then
-                ()
-              else
-                Path.rm_rf path
-          end
-        | exception _ ->
-          if not (Path.Table.mem t.files path) then Path.unlink path
-        | _ ->
-          if not (Path.Table.mem t.files path) then Path.unlink path)
+        let path_is_a_target = Path.Table.mem t.files path in
+        if path_is_a_target then ()
+        else
+          match Unix.lstat (Path.to_string path) with
+          | { st_kind = S_DIR; _ } -> begin
+              match subdirs_to_keep with
+              | All -> ()
+              | These set ->
+                if String.Set.mem set fn ||
+                  Path.Set.mem t.build_dirs_to_keep path then ()
+                else
+                  Path.rm_rf path
+            end
+          | exception _ -> Path.unlink path
+          | _ -> Path.unlink path)
 
 let no_rule_found =
   let fail fn ~loc =

src/utils.ml

@@ -203,13 +203,26 @@ module Cached_digest = struct
     ; table       = Hashtbl.create 1024
     }
 
+  let dir_digest stat =
+    let ints = stat.Unix.st_size + stat.st_perm in
+    (string_of_int ints ^
+     string_of_float stat.st_mtime ^
+     string_of_float stat.st_ctime)
+
+  let path_stat_digest fn stat =
+    if stat.Unix.st_kind = Unix.S_DIR then
+      dir_digest stat
+    else Digest.file (Path.to_string fn)
+
   let refresh fn =
-    let digest = Digest.file (Path.to_string fn) in
+    let path = Path.to_string fn in
+    let stat = Unix.stat path in
+    let digest = path_stat_digest fn stat in
     Hashtbl.replace cache.table ~key:fn
       ~data:{ digest
-            ; timestamp = (Unix.stat (Path.to_string fn)).st_mtime
+            ; timestamp = stat.st_mtime
             ; timestamp_checked = cache.checked_key
-            };
+      };
     digest
 
   let file fn =
@@ -218,9 +231,10 @@ module Cached_digest = struct
       if x.timestamp_checked = cache.checked_key then
         x.digest
       else begin
-        let mtime = (Unix.stat (Path.to_string fn)).st_mtime in
+        let stat = Unix.stat (Path.to_string fn) in
+        let mtime = stat.st_mtime in
         if mtime <> x.timestamp then begin
-          let digest = Digest.file (Path.to_string fn) in
+          let digest = path_stat_digest fn stat in
           x.digest    <- digest;
           x.timestamp <- mtime;
         end;