For in-memory tests, use the local root

Summary:
Because ModulePath directly accesses the filesystem to follow symlinks
(this is tech debt which could be eliminated by a proposed ModuleTracker
refactor to use abstract filesystems, but is necessary today), we have
to bypass `ModulePath.create` when using in-memory source code for unit tests.

This is unfortunate but okay. But because we have to bypass `ModulePath.create`,
we used `ModulePath.create_for_testing` which requires hardcoding the priority
of a search root.

This is a problem if we want to change the order of the search roots, as Kyle
is experimenting with doing in order to support a source-code fallback for Buck
projects while Buck is still running.

The fix is to avoid hardcoding a priority by using `Raw.create` to determine
the priority from the configuration. Because some other unit tests (unrelated
to ScratchProject and in-memory source code) do still require directly creating
a ModulePath we make a new function `create_for_in_memory_scratch_project`
to use specifically for this case.

Reviewed By: kinto0

Differential Revision: D50584161

fbshipit-source-id: 548dd602bcf7875aeaea9b17e5eee5b6b481cd6e

source/ast/modulePath.ml

@@ -185,14 +185,27 @@ let relative { raw = { Raw.relative; _ }; _ } = relative
 
 let is_in_project { is_external; _ } = not is_external
 
-let create_for_testing ~relative ~is_external ~priority =
-  let raw = Raw.{ relative; priority } in
+let create_from_raw_for_testing ~is_external ({ Raw.relative; _ } as raw) =
   let qualifier = qualifier_from_relative_path relative in
   let is_stub = PyrePath.is_path_python_stub relative in
   let is_init = PyrePath.is_path_python_init relative in
   { raw; qualifier; is_stub; is_external; is_init }
 
 
+let create_for_testing ~relative ~is_external ~priority =
+  let raw = Raw.{ relative; priority } in
+  create_from_raw_for_testing ~is_external raw
+
+
+let create_for_in_memory_scratch_project ~configuration ~relative ~is_external =
+  let raw =
+    let { Configuration.Analysis.local_root; _ } = configuration in
+    let path_in_local_root = PyrePath.create_relative ~root:local_root ~relative in
+    Raw.create ~configuration (ArtifactPath.create path_in_local_root) |> Option.value_exn
+  in
+  create_from_raw_for_testing ~is_external raw
+
+
 let full_path ~configuration { raw; _ } = Raw.full_path ~configuration raw
 
 (* NOTE: This comparator is expected to operate on SourceFiles that are mapped to the same module

source/ast/modulePath.mli

@@ -44,6 +44,12 @@ val relative : t -> string
 
 val is_in_project : t -> bool
 
+val create_for_in_memory_scratch_project
+  :  configuration:Configuration.Analysis.t ->
+  relative:string ->
+  is_external:bool ->
+  t
+
 val create_for_testing : relative:string -> is_external:bool -> priority:int -> t
 
 val qualifier_from_relative_path : string -> Reference.t

source/test/test.ml

@@ -3065,7 +3065,9 @@ module ScratchProject = struct
         let in_memory_sources =
           let to_in_memory_source (relative, content) ~is_external =
             let code = trim_extra_indentation content in
-            let module_path = ModulePath.create_for_testing ~relative ~is_external ~priority:1 in
+            let module_path =
+              ModulePath.create_for_in_memory_scratch_project ~configuration ~relative ~is_external
+            in
             module_path, code
           in
           List.map sources ~f:(to_in_memory_source ~is_external:false)