outdated: document and test last-one-wins behaviour of new-freeze flags

Cabal/doc/developing-packages.rst

@@ -1336,10 +1336,12 @@ The following flags are supported by the ``outdated`` command:
 ``--new-freeze-file``
     Read dependency version bounds from the new-style freeze file
     (``cabal.project.freeze``) instead of the package description file.
+    This is equivalent to ``--project-file cabal.project``.
 ``--project-file`` *PROJECTFILE*
     Read dependendency version bounds from the new-style freeze file
     related to the named project file (i.e., ``$PROJECTFILE.freeze``)
-    instead of the package desctription file.
+    instead of the package desctription file. If multiple ``--project-file``
+    flags are provided, only the final one is considered.
 ``--simple-output``
     Print only the names of outdated dependencies, one per line.
 ``--exit-code``

cabal-testsuite/PackageTests/Outdated/outdated-project-file.out

@@ -3,3 +3,13 @@ Downloading the latest package list from test-local-repo
 # cabal outdated
 Outdated dependencies:
 base ==3.0.3.2 (latest: 4.0.0.0)
+# cabal outdated
+Outdated dependencies:
+base ==3.0.3.2 (latest: 4.0.0.0)
+# cabal outdated
+Outdated dependencies:
+base ==3.0.3.2 (latest: 4.0.0.0)
+# cabal outdated
+Outdated dependencies:
+base ==3.0.3.2 (latest: 4.0.0.0)
+template-haskell ==2.3.0.0 (latest: 2.4.0.0)

cabal-testsuite/PackageTests/Outdated/outdated-project-file.test.hs

@@ -4,3 +4,15 @@ main = cabalTest $ withRepo "repo" $ do
   assertOutputContains "base" res
   assertOutputDoesNotContain "template-haskell" res
 
+  -- Test last-one-wins behaviour.
+  res <- cabal' "outdated" ["--project-file", "cabal.project", "--project-file", "variant.project"]
+  assertOutputContains "base" res
+  assertOutputDoesNotContain "template-haskell" res
+
+  res <- cabal' "outdated" ["--new-freeze-file", "--project-file", "variant.project"]
+  assertOutputContains "base" res
+  assertOutputDoesNotContain "template-haskell" res
+
+  res <- cabal' "outdated" ["--project-file", "variant.project", "--new-freeze-file"]
+  assertOutputContains "base" res
+  assertOutputContains "template-haskell" res