Merge pull request #4402 from rjbou/opamfile-loc-var

New package variable: `opamfile`

doc/pages/Manual.md

@@ -506,6 +506,9 @@ the package being defined.
 - <a id="pkgvar-build-id">`build-id`</a>:
   a hash identifying the precise package version and metadata, and that of all
   its dependencies
+- <a id="pkgvar-opamfile">`opamfile`</a>:
+  if the package is installed, path of its opam file, from opam internals,
+  otherwise not defined
 
 Extra variables can be defined by any package at installation time, using a
 [`<pkgname>.config`](#lt-pkgname-gt-config) file with a

master_changes.md

@@ -37,7 +37,7 @@ New option/command/subcommand are prefixed with ◈.
   *
 
 ## Var
-  *
+  * Add `opamfile-loc` as a package variable, containing the location of installed package opam file [#4402 @rjbou]
 
 ## Option
 

src/state/opamPackageVar.ml

@@ -46,6 +46,7 @@ let package_variable_names = [
   "dev",       "True if this is a development package";
   "build-id",  "A hash identifying the precise package version with all its \
                 dependencies";
+  "opamfile", "Path of the curent opam file";
 ]
 
 let predefined_depends_variables =
@@ -305,6 +306,21 @@ let resolve st ?opam:opam_arg ?(local=OpamVariable.Map.empty) v =
        with Not_found -> Some (string ""))
     | "dev", Some opam -> Some (bool (is_dev_package st opam))
     | "build-id", Some opam -> OpamStd.Option.map string (build_id st opam)
+    | "opamfile", Some opam ->
+      (* Opamfile path is retrieved from overlay directory for pinned packages,
+         or from temporary repository in /tmp *)
+      let repos_roots reponame =
+        match Hashtbl.find st.switch_repos.repos_tmp reponame with
+        | lazy repo_root -> repo_root
+        | exception Not_found ->
+          OpamRepositoryPath.root st.switch_global.root reponame
+      in
+      OpamFile.OPAM.get_metadata_dir ~repos_roots opam
+      |> OpamStd.Option.map (fun d ->
+          OpamFilename.Op.(d//"opam")
+          |> OpamFilename.to_string
+          |> string
+        )
     | _, _ -> None
   in
   let make_package_local v =