Display actual stanza when package is ambiguous

Previously we displayed `(install ...)` in all cases.

Closes #1123

Signed-off-by: Etienne Millon <me@emillon.org>

CHANGES.md

@@ -9,6 +9,8 @@ next
 
 - Highlight error locations in error messages (#1121, @emillon)
 
+- Display actual stanza when package is ambiguous (#1126, fix #1123, @emillon)
+
 1.1.1 (08/08/2018)
 ------------------
 

src/dune_file.ml

@@ -166,7 +166,7 @@ module Pkg = struct
            (Package.Name.to_string pkg.Package.name)
            (Path.to_string (Package.opam_file pkg))))
 
-  let default (project : Dune_project.t) =
+  let default (project : Dune_project.t) stanza =
     match Package.Name.Map.values project.packages with
     | [pkg] -> Ok pkg
     | [] ->
@@ -178,11 +178,12 @@ module Pkg = struct
     | _ :: _ :: _ ->
       Error
         (sprintf
-           "I can't determine automatically which package this (install ...) \
+           "I can't determine automatically which package this \
-            stanza is for. I have the choice between these ones:\n\
+            stanza is for.\nI have the choice between these ones:\n\
             %s\n\
-            You need to add a (package ...) field in this (install ...) stanza"
+            You need to add a (package ...) field to this (%s) stanza."
-           (listing (Package.Name.Map.values project.packages)))
+           (listing (Package.Name.Map.values project.packages))
+           stanza)
 
   let resolve (project : Dune_project.t) name =
     match Package.Name.Map.find project.packages name with
@@ -215,14 +216,14 @@ module Pkg = struct
     | Ok    x -> x
     | Error e -> Loc.fail loc "%s" e
 
-  let field =
+  let field stanza =
     map_validate
       (let%map p = Dune_project.get_exn ()
        and pkg = field_o "package" string in
        (p, pkg))
       ~f:(fun (p, pkg) ->
         match pkg with
-        | None -> default p
+        | None -> default p stanza
         | Some name -> resolve p (Package.Name.of_string name))
 end
 
@@ -1049,7 +1050,7 @@ module Install_conf = struct
     record
       (let%map section = field "section" Install.Section.t
        and files = field "files" (list file)
-       and package = Pkg.field
+       and package = Pkg.field "install"
        in
        { section
        ; files
@@ -1289,7 +1290,10 @@ module Executables = struct
           match
             match package with
             | None ->
-              (buildable.loc, Pkg.default project)
+              let stanza =
+                pluralize ~multi "executable"
+              in
+              (buildable.loc, Pkg.default project stanza)
             | Some (loc, name) ->
               (loc, Pkg.resolve project (Package.Name.of_string name))
           with
@@ -1705,7 +1709,7 @@ module Documentation = struct
 
   let t =
     record
-      (let%map package = Pkg.field
+      (let%map package = Pkg.field "documentation"
        and mld_files = Ordered_set_lang.field "mld_files"
        and loc = loc in
        { loc

test/blackbox-tests/dune.inc

@@ -708,6 +708,14 @@
    test-cases/select
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name several-packages)
+ (deps (package dune) (source_tree test-cases/several-packages))
+ (action
+  (chdir
+   test-cases/several-packages
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name shadow-bindings)
  (deps (package dune) (source_tree test-cases/shadow-bindings))
@@ -867,6 +875,7 @@
   (alias scope-bug)
   (alias scope-ppx-bug)
   (alias select)
+  (alias several-packages)
   (alias shadow-bindings)
   (alias subst)
   (alias syntax-versioning)
@@ -953,6 +962,7 @@
   (alias reporting-of-cycles)
   (alias scope-bug)
   (alias select)
+  (alias several-packages)
   (alias shadow-bindings)
   (alias subst)
   (alias syntax-versioning)

test/blackbox-tests/test-cases/several-packages/documentation/dune

@@ -0,0 +1 @@
+(documentation)

test/blackbox-tests/test-cases/several-packages/documentation/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

test/blackbox-tests/test-cases/several-packages/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

test/blackbox-tests/test-cases/several-packages/executable/dune

@@ -0,0 +1,3 @@
+(executable
+  (public_name an_executable)
+)

test/blackbox-tests/test-cases/several-packages/executable/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

test/blackbox-tests/test-cases/several-packages/install/dune

@@ -0,0 +1,4 @@
+(install
+ (section etc)
+ (files file.conf)
+)

test/blackbox-tests/test-cases/several-packages/install/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

test/blackbox-tests/test-cases/several-packages/run.t

@@ -0,0 +1,35 @@
+If two packages are available and no (package) is present, an error message is
+displayed. This can happen for:
+
+- (executable)
+
+  $ dune build --root executable
+  File "dune", line 1, characters 0-43:
+  Error: I can't determine automatically which package this stanza is for.
+  I have the choice between these ones:
+  - pkg1 (because of pkg1.opam)
+  - pkg2 (because of pkg2.opam)
+  You need to add a (package ...) field to this (executables) stanza.
+  [1]
+
+- (documentation)
+
+  $ dune build --root documentation
+  File "dune", line 1, characters 0-15:
+  Error: I can't determine automatically which package this stanza is for.
+  I have the choice between these ones:
+  - pkg1 (because of pkg1.opam)
+  - pkg2 (because of pkg2.opam)
+  You need to add a (package ...) field to this (documentation) stanza.
+  [1]
+
+- (install)
+
+  $ dune build --root install
+  File "dune", line 1, characters 0-44:
+  Error: I can't determine automatically which package this stanza is for.
+  I have the choice between these ones:
+  - pkg1 (because of pkg1.opam)
+  - pkg2 (because of pkg2.opam)
+  You need to add a (package ...) field to this (install) stanza.
+  [1]