Store ~p warning file relative to cwd

lib/phoenix/verified_routes.ex

@@ -321,9 +321,12 @@ defmodule Phoenix.VerifiedRoutes do
       test_path = split_test_path(route.test_path)
 
       unless route.router.verified_route?([], test_path) do
+        # The file is stored relative to the project, so expand it against the
+        # current directory here, where the warning is emitted. Mix persists
+        # warnings by their absolute source path and drops relative ones.
         IO.warn(
           "no route path for #{inspect(route.router)} matches #{route.inspected_route}",
-          route.warn_location
+          Keyword.update!(route.warn_location, :file, &Path.expand/1)
         )
       end
     end)
@@ -984,6 +987,10 @@ defmodule Phoenix.VerifiedRoutes do
 
   defp warn_location(meta, %{line: line, file: file, function: function, module: module}) do
     column = if column = meta[:column], do: column + 2
+    # Relative to the project, so copies of the project (git worktrees,
+    # copy-on-write clones) that reuse the build point to their own files.
+    # It is expanded again when the warning is emitted, see __verify__/1.
+    file = Path.relative_to_cwd(file)
     [line: line, function: function, module: module, file: file, column: column]
   end
 

test/phoenix/verified_routes_test.exs

@@ -734,6 +734,35 @@ defmodule Phoenix.VerifiedRoutesTest do
       :code.delete(__MODULE__.Unmatched)
     end
 
+    test "~p warning location resolves to the current directory" do
+      {_, diagnostics} =
+        Code.with_diagnostics(fn ->
+          defmodule WarnLocation do
+            use Phoenix.VerifiedRoutes, endpoint: unquote(@endpoint), router: unquote(@router)
+
+            def test, do: ~p"/unknown"
+          end
+        end)
+
+      assert [%{file: file} = diagnostic] = diagnostics
+
+      assert diagnostic.message =~
+               ~s|no route path for Phoenix.VerifiedRoutesTest.Router matches "/unknown"|
+
+      # the file is stored relative to the project and expanded when the
+      # warning is emitted, which Mix needs to persist the warning
+      assert Path.expand(file) == __ENV__.file
+
+      # Elixir 1.15 always reports IO.warn locations relative to the current directory
+      if Version.match?(System.version(), ">= 1.16.0") do
+        assert Path.type(file) == :absolute
+        assert diagnostic.source == file
+      end
+    after
+      :code.purge(__MODULE__.WarnLocation)
+      :code.delete(__MODULE__.WarnLocation)
+    end
+
     test "~p warns on warn_on_verify: true route" do
       warnings =
         ExUnit.CaptureIO.capture_io(:stderr, fn ->