feat(exec): support absolute paths for dune exec

bin/exec.ml

@@ -136,18 +136,19 @@ let get_path common sctx ~prog =
      | true -> Memo.return path
      | false -> not_found_with_suggestions ~dir ~prog)
   | Absolute ->
-    (match
-       let prog = Path.of_string prog in
-       if Path.exists prog
-       then Some prog
-       else if not Sys.win32
-       then None
-       else (
-         let prog = Path.extend_basename prog ~suffix:Bin.exe in
-         Option.some_if (Path.exists prog) prog)
-     with
-     | Some prog -> Memo.return prog
-     | None -> not_found_with_suggestions ~dir ~prog)
+    let path =
+      Path.of_string prog
+      |> Path.Expert.try_localize_external
+      |> Path.to_string
+      |> Path.relative_to_source_in_build_or_external ~dir
+    in
+    if Path.equal (Path.external_ Path.External.root) path
+    then not_found ~hints:[] ~prog
+    else
+      Build_system.file_exists path
+      >>= (function
+       | true -> Memo.return path
+       | false -> not_found_with_suggestions ~dir ~prog)
 ;;
 
 let get_path_and_build_if_necessary common sctx ~no_rebuild ~prog =

doc/changes/12094.md

@@ -0,0 +1,2 @@
+- `dune exec` now accepts absolute paths inside the workspace. (#12094,
+  @Alizter)

test/blackbox-tests/test-cases/exec/exec-abs.t

@@ -0,0 +1,38 @@
+Testing interaction of dune exec and absolute directories.
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.20)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (executable
+  >  (name foo))
+  > EOF
+
+  $ cat > foo.ml <<EOF
+  > let () = print_endline "hi" ;;
+  > EOF
+
+  $ dune exec ./foo.exe
+  hi
+
+Dune exec is able to handle absolute executable paths.
+
+  $ dune exec $PWD/foo.exe
+  hi
+
+Lets check some validation:
+
+  $ dune exec ..
+  Error: Program '..' not found!
+  [1]
+  $ dune exec .
+  Error: Program '.' not found!
+  [1]
+  $ dune exec /.
+  Error: Program '/.' not found!
+  [1]
+  $ dune exec /
+  Error: Program '/' not found!
+  [1]
+