Add support for passing arguments to instrumentation backends

CHANGES.md

@@ -69,6 +69,9 @@ Unreleased
 - `dune describe` now also includes information about executables in addition to
   that of libraries. (#3892, #3895, @nojb)
 
+- instrumentations backends can now receive arguments via `(instrumentation
+  (backend <name> <args>))`. (#3906, #3932, @nojb)
+
 2.7.1 (2/09/2020)
 -----------------
 

doc/instrumentation.rst

@@ -23,7 +23,9 @@ executable stanza:
    (library
     (name ...)
     (instrumentation
-     (backend <name>)))
+     (backend <name> <args>)))
+
+The backend ``<name>`` can be passed arguments using ``<args>``.
 
 This field can be repeated multiple times in order to support various
 backends. For instance:
@@ -33,7 +35,7 @@ backends. For instance:
    (library
     (name foo)
     (modules foo)
-    (instrumentation (backend bisect_ppx))
+    (instrumentation (backend bisect_ppx --bisect-silent yes))
     (instrumentation (backend landmarks)))
 
 This will instruct Dune that when either the ``bisect_ppx`` or ``landmarks``

src/dune_rules/dune_file.ml

@@ -231,15 +231,21 @@ module Buildable = struct
       located
         (multi_field "instrumentation"
            ( Dune_lang.Syntax.since Stanza.syntax (2, 7)
-           >>> fields (field "backend" (located Lib_name.decode)) ))
+           >>> fields
+                 (field "backend"
+                    (let+ libname = located Lib_name.decode
+                     and+ flags = repeat String_with_vars.decode in
+                     (libname, flags))) ))
     in
     let preprocess =
       let init =
         let f libname = Preprocess.With_instrumentation.Ordinary libname in
         Module_name.Per_item.map preprocess ~f:(Preprocess.map ~f)
       in
       List.fold_left instrumentation
-        ~f:(Preprocess.Per_module.add_instrumentation ~loc:loc_instrumentation)
+        ~f:(fun accu (instrumentation, flags) ->
+          Preprocess.Per_module.add_instrumentation accu
+            ~loc:loc_instrumentation ~flags instrumentation)
         ~init
     in
     let foreign_stubs =

src/dune_rules/preprocess.ml

@@ -197,19 +197,18 @@ module Per_module = struct
     else
       No_preprocessing
 
-  let add_instrumentation t ~loc libname =
+  let add_instrumentation t ~loc ~flags:flags' libname =
     Per_module.map t ~f:(fun pp ->
         match pp with
         | No_preprocessing ->
           let pps = [ With_instrumentation.Instrumentation_backend libname ] in
-          let flags = [] in
           let staged = false in
-          Pps { loc; pps; flags; staged }
+          Pps { loc; pps; flags = flags'; staged }
         | Pps { loc; pps; flags; staged } ->
           let pps =
             With_instrumentation.Instrumentation_backend libname :: pps
           in
-          Pps { loc; pps; flags; staged }
+          Pps { loc; pps; flags = flags @ flags'; staged }
         | Action (loc, _)
         | Future_syntax loc ->
           User_error.raise ~loc

src/dune_rules/preprocess.mli

@@ -77,6 +77,7 @@ module Per_module : sig
   val add_instrumentation :
        With_instrumentation.t t
     -> loc:Loc.t
+    -> flags:String_with_vars.t list
     -> Loc.t * Lib_name.t
     -> With_instrumentation.t t
 

test/blackbox-tests/test-cases/instrumentation.t/ppx/hello.ml

@@ -1 +1 @@
-let hello () = print_endline "Hello, Dune!"
+let hello s = print_endline (Printf.sprintf "Hello from %s!" s)

test/blackbox-tests/test-cases/instrumentation.t/ppx/hello_ppx.ml

@@ -1,12 +1,23 @@
 open Ast_helper
 open Longident
 
+let place = ref None
+
 let impl str =
+  let arg =
+    match !place with
+    | None -> Exp.ident (Location.mknoloc (Lident "__MODULE__"))
+    | Some s -> Exp.constant (Const.string s)
+  in
   Str.eval
     (Exp.apply (Exp.ident (Location.mknoloc (Ldot (Lident "Hello", "hello"))))
-       [Nolabel, Exp.construct (Location.mknoloc (Lident "()")) None]) :: str
+       [Nolabel, arg]) :: str
 
 open Ppxlib
 
+let () =
+  Driver.add_arg "-place" (Arg.String (fun s -> place := Some s))
+    ~doc:"PLACE where to say hello from"
+
 let () =
   Driver.register_transformation_using_ocaml_current_ast ~impl "hello"

test/blackbox-tests/test-cases/instrumentation.t/run.t

@@ -1,5 +1,6 @@
   $ cat >dune-project <<EOF
   > (lang dune 2.7)
+  > (wrapped_executables false)
   > EOF
 
 "Hello" is an instrumentation backend that instruments by printing "Hello,
@@ -18,7 +19,7 @@ Dune!" at the beginning of the module.
   > EOF
 
   $ cat >mylib.ml <<EOF
-  > let f () = print_endline "Mylib"
+  > let f () = ()
   > EOF
 
   $ cat >main.ml <<EOF
@@ -30,16 +31,14 @@ message.
 
   $ dune build
   $ _build/default/main.exe
-  Mylib
 
 This should print the instrumentation message twice, once for "main" and once
 for "mylib":
 
   $ dune build --instrument-with hello
   $ _build/default/main.exe
-  Hello, Dune!
-  Hello, Dune!
-  Mylib
+  Hello from Mylib!
+  Hello from Main!
 
 An empty file:
 
@@ -61,14 +60,27 @@ We rebuild with instrumentation via the CLI.
 We get the message.
 
   $ _build/default/main.exe
-  Hello, Dune!
+  Hello from Main!
+
+We also check that we can pass arguments to the ppx.
+
+  $ cat >dune <<EOF
+  > (executable
+  >  (name main)
+  >  (modules main)
+  >  (instrumentation (backend hello -place Spain)))
+  > EOF
+
+  $ dune build --instrument-with hello
+  $ _build/default/main.exe
+  Hello from Spain!
 
 Can also enable with an environment variable.
 
   $ DUNE_INSTRUMENT_WITH=hello dune build
 
   $ _build/default/main.exe
-  Hello, Dune!
+  Hello from Spain!
 
 Instrumentation can also be controlled by using the dune-workspace file.
 
@@ -80,7 +92,7 @@ Instrumentation can also be controlled by using the dune-workspace file.
   $ dune build
 
   $ _build/default/main.exe
-  Hello, Dune!
+  Hello from Spain!
 
 It can also be controlled on a per-context scope.
 
@@ -92,7 +104,7 @@ It can also be controlled on a per-context scope.
   $ dune build
 
   $ _build/coverage/main.exe
-  Hello, Dune!
+  Hello from Spain!
 
 Per-context setting takes precedence over per-workspace setting.
 
@@ -119,6 +131,7 @@ Next, we check the backend can be used when it is installed.
   > EOF
   $ cat >installed/dune-project <<EOF
   > (lang dune 2.7)
+  > (wrapped_executables false)
   > EOF
   $ cat >installed/dune <<EOF
   > (executable
@@ -130,4 +143,4 @@ Next, we check the backend can be used when it is installed.
   $ OCAMLPATH=$PWD/_install/lib dune build --root installed
   Entering directory 'installed'
   $ installed/_build/default/main.exe
-  Hello, Dune!
+  Hello from Main!