commit: only call a variable updated when its value changed

The summaries generated from the sourced bash env intersected the names on
the removed and added sides of the diff, without checking the value. Any
change to a watched variable's declare line counted, gaining the export
attribute or being requoted, so the summary announced an update to something
the commit never touched. Compare the values instead.

Resolves: #115
Signed-off-by: Arthur Zamarin <arthurzam@gentoo.org>

Author: arthurzam

NEWS.rst

@@ -33,6 +33,10 @@ pkgdev 0.2.18 (unreleased)
 - commit: the mangler now adds the blank line after the ``EAPI=`` assignment
   (Arthur Zamarin, #127)
 
+- commit: the generated summary no longer claims a variable was updated when
+  only its ``declare`` line differs, as when it gains the export attribute
+  while its value stays put (Arthur Zamarin, #115)
+
 **pkgdev showkw:**
 
 - showkw: drop the vendored copy of tabulate in favor of a dependency on

src/pkgdev/scripts/pkgdev_commit.py

@@ -586,7 +586,9 @@ def modify(self):
                 }
                 targets = array_targets | string_targets
 
-                updated_vars = drop.keys() & add.keys()
+                updated_vars = {
+                    name for name in drop.keys() & add.keys() if drop[name] != add[name]
+                }
                 if updated := sorted(watch_vars & updated_vars):
                     summaries.add(f"update {', '.join(updated)}")
                 elif (target := targets & updated_vars) and len(target) == 1:

tests/scripts/test_pkgdev_commit.py

@@ -562,6 +562,16 @@ def test_generated_commit_summaries(self, capsys, repo, make_git_repo):
         )
         assert commit() == "cat/pkg: update DESCRIPTION, HOMEPAGE"
 
+        # a declare line differing only in its attributes is not an update:
+        # exporting the var leaves its value alone
+        repo.create_ebuild(
+            "cat/pkg-7",
+            description="another something",
+            homepage="https://gentoo.org",
+            data="export DESCRIPTION\n",
+        )
+        assert commit() == "cat/pkg: summary"
+
         # update string_targets (USE_RUBY)
         os.mkdir(pjoin(repo.location, "profiles", "desc"))
         with open(pjoin(repo.path, "profiles", "desc", "ruby_targets.desc"), "w") as file: