Do not leak "private" fields into export

Fields starting with underscore, `_`, are considered "private" and
should not be exported.

This is a "dirty" workaround to fix #1729, a proper fix would probably
turn the table around, and instead of hiding some fields it would export
only fields marked for export. That should be implemented later for #1688.

Fixes #1729.

tests/plan/export/data/plan.fmf

@@ -25,3 +25,9 @@ execute:
       - merge-pull-request
       - add-build-to-update
       - add-build-to-compose
+
+/remote:
+    plan:
+        import:
+            url: https://github.com/teemtee/tmt
+            name: /plans/features/basic

tests/plan/export/test.sh

@@ -16,6 +16,7 @@ rlJournalStart
         rlAssertGrep "- name: /plan/gate" $rlRun_LOG
         rlAssertGrep "discover:" $rlRun_LOG
         rlAssertGrep "execute:" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "tmt plan export /plan/basic"
@@ -24,6 +25,7 @@ rlJournalStart
         rlAssertGrep "summary: Just basic keys." $rlRun_LOG
         rlAssertGrep "discover:" $rlRun_LOG
         rlAssertGrep "execute:" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "tmt plan export /plan/context"
@@ -34,6 +36,7 @@ rlJournalStart
         rlAssertGrep "execute:" $rlRun_LOG
         rlAssertGrep "context:" $rlRun_LOG
         rlAssertGrep "component: dash" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "tmt plan export /plan/environment"
@@ -44,6 +47,7 @@ rlJournalStart
         rlAssertGrep "execute:" $rlRun_LOG
         rlAssertGrep "environment:" $rlRun_LOG
         rlAssertGrep "RELEASE: f35" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "tmt plan export /plan/gate"
@@ -56,6 +60,7 @@ rlJournalStart
         rlAssertGrep "- merge-pull-request" $rlRun_LOG
         rlAssertGrep "- add-build-to-update" $rlRun_LOG
         rlAssertGrep "- add-build-to-compose" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "Invalid format"

tests/story/export/test.sh

@@ -11,6 +11,7 @@ rlJournalStart
         rlAssertGrep "name: /mini" $rlRun_LOG
         rlAssertGrep "order: 50" $rlRun_LOG
         rlAssertGrep "story: As a user I want this and that" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
     rlPhaseEnd
 
     rlPhaseStartTest "Export to yaml (full story)"
@@ -25,6 +26,7 @@ rlJournalStart
         rlAssertGrep "story: As a user I want this and that" $rlRun_LOG
         rlAssertGrep "title: A Concise Title" $rlRun_LOG
         rlAssertGrep "priority: must have" $rlRun_LOG
+        rlAssertNotGrep " _" $rlRun_LOG
         rlRun "grep -A1 ^link: $rlRun_LOG | grep -- ' - implemented-by: /some/code.py'"
         rlRun "grep -A1 ^tag: $rlRun_LOG | grep -- '- foo'"
         rlRun "grep -A1 ^example: $rlRun_LOG | grep -- '- An inspiring example'"

tests/test/export/test.sh

@@ -26,12 +26,14 @@ rlJournalStart
         rlPhaseStartTest "$cmd"
             rlRun -s "$cmd" 0 "Export test"
             rlAssertGrep "'name': '$tname'" $rlRun_LOG
+            rlAssertNotGrep "'_" $rlRun_LOG
         rlPhaseEnd
 
         cmd="tmt tests export --format yaml $tname"
         rlPhaseStartTest "$cmd"
             rlRun -s "$cmd" 0 "Export test"
             rlAssertGrep "name: $tname" $rlRun_LOG
+            rlAssertNotGrep " _" $rlRun_LOG
         rlPhaseEnd
     done
 
@@ -61,12 +63,14 @@ rlJournalStart
         rlPhaseStartTest "$cmd"
             rlRun -s "$cmd" 0 "Export test"
             rlAssertGrep "'name': '$tname'" $rlRun_LOG
+            rlAssertNotGrep "'_" $rlRun_LOG
         rlPhaseEnd
 
         cmd="tmt tests export --format yaml --fmf-id $tname"
         rlPhaseStartTest "$cmd"
             rlRun -s "$cmd" 0 "Export test"
             rlAssertGrep "name: $tname" $rlRun_LOG
+            rlAssertNotGrep " _" $rlRun_LOG
         rlPhaseEnd
     done
 

tmt/base.py

@@ -539,6 +539,12 @@ def export(self, *, format_: ExportFormat = ExportFormat.YAML,
         # Always include node name, add requested keys, ignore adjust
         data: Dict[str, Any] = dict(name=self.name)
         for key in keys:
+            # TODO: provide more mature solution for https://github.com/teemtee/tmt/issues/1688
+            # Untile that, do not export fields that start with an underscore, to avoid leaking
+            # "private" object members.
+            if key.startswith('_'):
+                continue
+
             if key == 'adjust':
                 continue