feat: support libraries with the same name in multiple contexts

bin/describe/describe_workspace.ml

@@ -451,7 +451,8 @@ module Crawl = struct
           let* modules_, obj_dir_ =
             Dir_contents.get sctx ~dir:(Path.as_in_build_dir_exn src_dir)
             >>= Dir_contents.ocaml
-            >>| Ml_sources.modules_and_obj_dir ~for_:(Library name)
+            >>| Ml_sources.modules_and_obj_dir
+                  ~for_:(Library (Lib_info.lib_id info |> Lib_id.to_local_exn))
           in
           let* pp_map =
             let+ version =

doc/changes/10307.md

@@ -0,0 +1,4 @@
+- allow libraries with the same `(name ..)` in projects as long as they don't
+  conflict during resolution (via `enabled_if`). (#10307, @anmonteiro,
+  @jchavarri)
+

src/dune_rules/dir_contents.ml

@@ -456,8 +456,8 @@ let modules_of_local_lib sctx lib =
     let dir = Lib_info.src_dir info in
     get sctx ~dir
   in
-  let name = Lib_info.name info in
-  ocaml t >>| Ml_sources.modules ~for_:(Library name)
+  ocaml t
+  >>| Ml_sources.modules ~for_:(Library (Lib_info.lib_id info |> Lib_id.to_local_exn))
 ;;
 
 let modules_of_lib sctx lib =

src/dune_rules/dune_package.ml

@@ -231,6 +231,7 @@ module Lib = struct
        let entry_modules = Modules.entry_modules modules |> List.map ~f:Module.name in
        let info : Path.t Lib_info.t =
          let src_dir = Obj_dir.dir obj_dir in
+         let lib_id = Lib_id.External (loc, name) in
          let enabled = Memo.return Lib_info.Enabled_status.Normal in
          let status =
            match Lib_name.analyze name with
@@ -255,6 +256,7 @@ module Lib = struct
            ~path_kind:External
            ~loc
            ~name
+           ~lib_id
            ~kind
            ~status
            ~src_dir

src/dune_rules/dune_rules.ml

@@ -24,6 +24,7 @@ module Expander = Expander
 module Lib = Lib
 module Lib_flags = Lib_flags
 module Lib_info = Lib_info
+module Lib_id = Lib_id
 module Modules = Modules
 module Module_compilation = Module_compilation
 module Exe_rules = Exe_rules

src/dune_rules/findlib.ml

@@ -206,10 +206,13 @@ let to_dune_library (t : Findlib.Package.t) ~dir_contents ~ext_lib ~external_loc
                     | Error e -> Error e))))
     in
     let modules = Lib_info.Source.External None in
+    let name = t.name in
+    let lib_id = Lib_id.External (loc, name) in
     Lib_info.create
       ~loc
       ~path_kind:External
-      ~name:t.name
+      ~name
+      ~lib_id
       ~kind
       ~status
       ~src_dir

src/dune_rules/gen_rules.ml

@@ -111,7 +111,11 @@ end = struct
       let+ () = Toplevel.Stanza.setup ~sctx ~dir ~toplevel in
       empty_none
     | Library.T lib ->
-      let* enabled_if = Lib.DB.available (Scope.libs scope) (Library.best_name lib) in
+      let* enabled_if =
+        Lib.DB.available_by_lib_id
+          (Scope.libs scope)
+          (Local (Library.to_lib_id ~src_dir lib))
+      in
       if_available_buildable
         ~loc:lib.buildable.loc
         (fun () -> Lib_rules.rules lib ~sctx ~dir ~scope ~dir_contents ~expander)

src/dune_rules/install_rules.ml

@@ -88,7 +88,10 @@ end = struct
   let lib_files ~dir_contents ~dir ~lib_config lib =
     let+ modules =
       let+ ml_sources = Dir_contents.ocaml dir_contents in
-      Some (Ml_sources.modules ml_sources ~for_:(Library (Lib_info.name lib)))
+      Some
+        (Ml_sources.modules
+           ml_sources
+           ~for_:(Library (Lib_info.lib_id lib |> Lib_id.to_local_exn)))
     and+ foreign_archives =
       match Lib_info.virtual_ lib with
       | None -> Memo.return (Mode.Map.Multi.to_flat_list @@ Lib_info.foreign_archives lib)
@@ -181,7 +184,9 @@ end = struct
     let lib_name = Library.best_name lib in
     let* installable_modules =
       let+ modules =
-        Dir_contents.ocaml dir_contents >>| Ml_sources.modules ~for_:(Library lib_name)
+        Dir_contents.ocaml dir_contents
+        >>| Ml_sources.modules
+              ~for_:(Library (Lib_info.lib_id info |> Lib_id.to_local_exn))
       and+ impl = Virtual_rules.impl sctx ~lib ~scope in
       Vimpl.impl_modules impl modules |> Modules.split_by_lib
     in
@@ -338,7 +343,15 @@ end = struct
         if enabled_if
         then
           if lib.optional
-          then Lib.DB.available (Scope.libs scope) (Library.best_name lib)
+          then (
+            let src_dir =
+              Expander.dir expander
+              |> Path.build
+              |> Path.drop_optional_build_context_src_exn
+            in
+            Lib.DB.available_by_lib_id
+              (Scope.libs scope)
+              (Local (Library.to_lib_id ~src_dir lib)))
           else Memo.return true
         else Memo.return false
       | Documentation.T _ -> Memo.return true
@@ -652,7 +665,9 @@ end = struct
             |> Foreign.Sources.object_files ~dir ~ext_obj
             |> List.map ~f:Path.build
           and* modules =
-            Dir_contents.ocaml dir_contents >>| Ml_sources.modules ~for_:(Library name)
+            Dir_contents.ocaml dir_contents
+            >>| Ml_sources.modules
+                  ~for_:(Library (Lib_info.lib_id info |> Lib_id.to_local_exn))
           and* melange_runtime_deps = file_deps (Lib_info.melange_runtime_deps info)
           and* public_headers = file_deps (Lib_info.public_headers info) in
           let+ dune_lib =