fix: improve cycle error messages

Add human readable descriptions to various memoization functions

Signed-off-by: Rudi Grinberg <[email protected]>

src/dune_engine/build_system.ml

@@ -2235,6 +2235,11 @@ end = struct
 
     let eval_memo =
       Memo.create "eval-pred"
+        ~human_readable_description:(fun glob ->
+          Pp.concat
+            [ Pp.textf "evaluating predicate in directory %s"
+                (Path.to_string_maybe_quoted (File_selector.dir glob))
+            ])
         ~input:(module File_selector)
         ~cutoff:Path.Set.equal eval_impl
 

src/dune_rules/dir_contents.ml

@@ -356,7 +356,13 @@ end = struct
             Path.Build.Map.of_list_map_exn subdirs ~f:(fun x -> (x.dir, x))
         }
 
-  let memo0 = Memo.create "dir-contents-get0" ~input:(module Key) get0_impl
+  let memo0 =
+    Memo.create "dir-contents-get0"
+      ~input:(module Key)
+      ~human_readable_description:(fun (_, dir) ->
+        Pp.textf "Computing directory contents of %s"
+          (Path.to_string_maybe_quoted (Path.build dir)))
+      get0_impl
 
   let get sctx ~dir =
     Memo.exec memo0 (sctx, dir) >>= function

src/dune_rules/install_rules.ml

@@ -922,13 +922,20 @@ let memo =
   in
   Memo.create
     ~input:(module Sctx_and_package)
+    ~human_readable_description:(fun (_, pkg) ->
+      Pp.textf "Computing installable artifacts for package %s"
+        (Package.Name.to_string (Package.name pkg)))
     "install-rules-and-pkg-entries"
     (fun (sctx, pkg) ->
       Memo.Build.return
         (let ctx = Super_context.context sctx in
          let context_name = ctx.name in
          let rules =
-           Memo.lazy_ ~name:"install-rules-and-pkg-entries-rules" (fun () ->
+           Memo.lazy_ ~name:"install-rules-and-pkg-entries-rules"
+             ~human_readable_description:(fun () ->
+               Pp.textf "Computing rules for package %s"
+                 (Package.Name.to_string (Package.name pkg)))
+             (fun () ->
                Rules.collect_unit (fun () ->
                    let* () = install_rules sctx pkg in
                    install_alias ctx pkg))

test/blackbox-tests/test-cases/reporting-of-cycles.t/run.t

@@ -79,79 +79,10 @@ This is a reproduction case from issue #4345
   > (copy_files (files ../file))
   > EOF
   $ dune build --root .
-  Internal error, please report upstream including the contents of _build/log.
-  Description:
-    ("internal dependency cycle",
-    { frames =
-        [ ("eval-pred",
-          { dir = In_build_dir "default"
-          ; predicate = { id = Glob "file" }
-          ; only_generated_files = false
-          })
-        ; ("dir-contents-get0", ("default", "default/lib"))
-        ; ("stanzas-to-entries", "default")
-        ; ("install-rules-and-pkg-entries-rules", ())
-        ; ("evaluate-restrict", ())
-        ; ("restrict-by-child-non-default-inner", ())
-        ; ("restrict-rules-here", ())
-        ; ("load-dir", In_build_dir "default")
-        ]
-    })
-  Raised at Memo.Exec.exec_dep_node.(fun) in file "src/memo/memo.ml", line
-    1338, characters 31-64
-  Called from Fiber.Execution_context.apply in file "src/fiber/fiber.ml", line
-    182, characters 9-14
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  Re-raised at Stdune__Exn.raise_with_backtrace in file
-    "otherlibs/stdune-unstable/exn.ml", line 36, characters 27-56
-  Called from Fiber.Execution_context.run_jobs in file "src/fiber/fiber.ml",
-    line 204, characters 8-13
-  -> required by ("build-alias", { dir = "default"; name = "default" })
-  -> required by ("toplevel", ())
-
-  I must not crash.  Uncertainty is the mind-killer. Exceptions are the
-  little-death that brings total obliteration.  I will fully express my cases. 
-  Execution will pass over me and through me.  And when it has gone past, I
-  will unwind the stack along its path.  Where the cases are handled there will
-  be nothing.  Only I will remain.
+  Error: Dependency cycle between:
+     Computing rules for package lib
+  -> evaluating predicate in directory _build/default
+  -> Computing directory contents of _build/default/lib
+  -> Computing rules for package lib
   [1]
   $ cd ..