fix(pkg): compare compiler packages semantically

bin/lock_dev_tool.ml

@@ -197,28 +197,46 @@ let lockdir_status dev_tool =
            with
            | false -> Memo.return (`Lockdir_ok_with_tool_pkg pkg)
            | true ->
-             let open Memo.O in
-             let* compiler = compiler_package () in
+             let+ compiler = compiler_package () in
              (match Package_name.Map.find packages compiler.info.name with
-              | None -> Memo.return `No_compiler_lockfile_in_lockdir
-              | Some pkg ->
-                let+ ocaml_compiler = compiler_package () in
-                (match Lock_dir.Pkg.equal pkg ocaml_compiler with
-                 | true -> `Lockdir_ok_with_tool_pkg pkg
-                 | false ->
-                   `Dev_tool_needs_to_be_relocked_because_project_compiler_version_changed
-                     (User_message.make
-                        [ Pp.textf
-                            "The version of the compiler package (%S) in this project's \
-                             lockdir has changed to %s (formerly the compiler version \
-                             was %s). The dev-tool %S will be re-locked and rebuilt with \
-                             this version of the compiler."
-                            (Package_name.to_string compiler.info.name)
-                            (Package_version.to_string ocaml_compiler.info.version)
-                            (Package_version.to_string pkg.info.version)
-                            (Dune_pkg.Dev_tool.package_name dev_tool
-                             |> Package_name.to_string)
-                        ]))))))
+              | None -> `No_compiler_lockfile_in_lockdir
+              | Some locked_compiler ->
+                let same_compiler_package =
+                  Lock_dir.Pkg.equal_on_platform locked_compiler compiler ~platform
+                in
+                if same_compiler_package
+                then `Lockdir_ok_with_tool_pkg pkg
+                else (
+                  let compiler_name = Package_name.to_string compiler.info.name in
+                  let dev_tool_name =
+                    Dune_pkg.Dev_tool.package_name dev_tool |> Package_name.to_string
+                  in
+                  let message =
+                    if
+                      Package_version.equal
+                        compiler.info.version
+                        locked_compiler.info.version
+                    then
+                      Pp.textf
+                        "The compiler package (%S) in this project's lockdir has changed \
+                         without changing its version (%s). The dev-tool %S will be \
+                         re-locked and rebuilt with the updated compiler package."
+                        compiler_name
+                        (Package_version.to_string compiler.info.version)
+                        dev_tool_name
+                    else
+                      Pp.textf
+                        "The version of the compiler package (%S) in this project's \
+                         lockdir has changed to %s (formerly the compiler version was \
+                         %s). The dev-tool %S will be re-locked and rebuilt with this \
+                         version of the compiler."
+                        compiler_name
+                        (Package_version.to_string compiler.info.version)
+                        (Package_version.to_string locked_compiler.info.version)
+                        dev_tool_name
+                  in
+                  `Dev_tool_needs_to_be_relocked_because_project_compiler_changed
+                    (User_message.make [ message ]))))))
 ;;
 
 (* [lock_dev_tool_at_version dev_tool version] generates the lockdir for the
@@ -261,7 +279,7 @@ let lock_dev_tool_at_version dev_tool version =
             "ocaml"
         ];
       true
-    | `Dev_tool_needs_to_be_relocked_because_project_compiler_version_changed message ->
+    | `Dev_tool_needs_to_be_relocked_because_project_compiler_changed message ->
       Console.print_user_message message;
       true
     | `Lockdir_missing_entry_for_tool message ->

doc/changes/fixed/16173.md

@@ -0,0 +1,3 @@
+- Avoid unnecessarily relocking and rebuilding dev tools when the project's
+  compiler package is unchanged, while still relocking after same-version
+  compiler recipe changes. (#16173, @Alizter)

src/dune_pkg/lock_dir.ml

@@ -966,6 +966,28 @@ module Pkg = struct
     List.is_empty t.enabled_on_platforms
     || Solver_env_disjunction.matches_platform t.enabled_on_platforms ~platform
   ;;
+
+  let equal_on_platform a b ~platform =
+    match is_enabled_on_platform a ~platform, is_enabled_on_platform b ~platform with
+    | false, false -> true
+    | true, false | false, true -> false
+    | true, true ->
+      let choose choice =
+        match Conditional_choice.choose_for_platform choice ~platform with
+        | None -> Conditional_choice.empty
+        | Some value -> Conditional_choice.singleton Solver_env.empty value
+      in
+      let normalize pkg =
+        { pkg with
+          build_command = choose pkg.build_command
+        ; install_command = choose pkg.install_command
+        ; depends = choose pkg.depends
+        ; enabled_on_platforms = [ Solver_env.empty ]
+        }
+        |> remove_locs
+      in
+      equal (normalize a) (normalize b)
+  ;;
 end
 
 module Repositories = struct

src/dune_pkg/lock_dir.mli

@@ -73,6 +73,12 @@ module Pkg : sig
 
   val remove_locs : t -> t
   val equal : t -> t -> bool
+
+  (** Compare package behavior on a platform, ignoring source locations, choices
+      for other platforms, and availability on other platforms. Packages disabled
+      on the platform compare equal if both are disabled. *)
+  val equal_on_platform : t -> t -> platform:Solver_env.t -> bool
+
   val hash : t -> int
   val digest_feed : t Dune_digest.Feed.t
   val to_dyn : t -> Dyn.t

test/blackbox-tests/test-cases/pkg/merlin/dev-tool-merlin-relock-on-ocaml-package-change.t

@@ -23,7 +23,7 @@ Use an extra file to distinguish reuse from an identical regenerated lockdir.
   > else
   >   echo 'unchanged dev-tool lock regenerated'
   > fi
-  unchanged dev-tool lock regenerated
+  unchanged dev-tool lock reused
   $ rm -f "${dev_tool_lock_dir}"/relock-sentinel
 
 Change the compiler package's build recipe without changing its version, then
@@ -42,10 +42,9 @@ Executing Merlin must notice the changed compiler package and regenerate its
 lock directory from the updated recipe.
 
   $ dune tools exec ocamlmerlin
-  The version of the compiler package ("ocaml-base-compiler") in this project's
-  lockdir has changed to 5.2.0 (formerly the compiler version was 5.2.0). The
-  dev-tool "merlin" will be re-locked and rebuilt with this version of the
-  compiler.
+  The compiler package ("ocaml-base-compiler") in this project's lockdir has
+  changed without changing its version (5.2.0). The dev-tool "merlin" will be
+  re-locked and rebuilt with the updated compiler package.
   Solution for _build/.dev-tools.locks/merlin:
   - merlin.0.0.1
   - ocaml-base-compiler.5.2.0

test/blackbox-tests/test-cases/pkg/merlin/dev-tool-merlin-relock-on-ocaml-version-change.t

@@ -29,14 +29,6 @@ Initially merlin will depend on ocaml-base-compiler.5.2.0 to match the project.
 
 We can re-run "dune tools exec ocamlmerlin" without relocking or rebuilding.
   $ dune tools exec ocamlmerlin
-  The version of the compiler package ("ocaml-base-compiler") in this project's
-  lockdir has changed to 5.2.0 (formerly the compiler version was 5.2.0). The
-  dev-tool "merlin" will be re-locked and rebuilt with this version of the
-  compiler.
-  Solution for _build/.dev-tools.locks/merlin:
-  - merlin.0.0.1
-  - ocaml-base-compiler.5.2.0
-  - ocaml-compiler.5.2.0
        Running 'ocamlmerlin'
   hello from fake ocamlmerlin
 

test/blackbox-tests/test-cases/pkg/ocamllsp/dev-tool-ocamllsp-pinned-compiler.t

@@ -56,12 +56,5 @@ rather than "ocaml-base-compiler.5.2.0" from opam-repository.
   - ocaml-lsp-server.0.0.1
 
   $ dune tools exec ocamllsp
-  The version of the compiler package ("ocaml-base-compiler") in this project's
-  lockdir has changed to dev (formerly the compiler version was dev). The
-  dev-tool "ocaml-lsp-server" will be re-locked and rebuilt with this version
-  of the compiler.
-  Solution for _build/.dev-tools.locks/ocaml-lsp-server:
-  - ocaml-base-compiler.dev
-  - ocaml-lsp-server.0.0.1
        Running 'ocamllsp'
   hello from fake ocamllsp

test/blackbox-tests/test-cases/pkg/ocamllsp/dev-tool-ocamllsp-relock-on-ocaml-version-change.t

@@ -29,14 +29,6 @@ Initially ocamllsp will depend on ocaml-base-compiler.5.2.0 to match the project
 
 We can re-run "dune tools exec ocamllsp" without relocking or rebuilding.
   $ dune tools exec ocamllsp
-  The version of the compiler package ("ocaml-base-compiler") in this project's
-  lockdir has changed to 5.2.0 (formerly the compiler version was 5.2.0). The
-  dev-tool "ocaml-lsp-server" will be re-locked and rebuilt with this version
-  of the compiler.
-  Solution for _build/.dev-tools.locks/ocaml-lsp-server:
-  - ocaml-base-compiler.5.2.0
-  - ocaml-compiler.5.2.0
-  - ocaml-lsp-server.0.0.1
        Running 'ocamllsp'
   hello from fake ocamllsp
 

test/blackbox-tests/test-cases/pkg/odoc/dev-tool-odoc-relock-on-ocaml-version-change.t

@@ -34,14 +34,6 @@ Initially odoc will depend on ocaml-base-compiler.5.2.0 to match the project.
 
 We can re-run "dune ocaml doc" without relocking or rebuilding.
   $ DUNE_CONFIG__LOCK_DEV_TOOL=enabled dune ocaml doc
-  The version of the compiler package ("ocaml-base-compiler") in this project's
-  lockdir has changed to 5.2.0 (formerly the compiler version was 5.2.0). The
-  dev-tool "odoc" will be re-locked and rebuilt with this version of the
-  compiler.
-  Solution for _build/.dev-tools.locks/odoc:
-  - ocaml-base-compiler.5.2.0
-  - ocaml-compiler.5.2.0
-  - odoc.0.0.1
   hello from fake odoc
   hello from fake odoc
   File "_doc/_html/_unknown_", line 1, characters 0-0: