Implement a directive for disabling inheritance

As the first step for the special `fmf` directives let's allow to
completely disable inheriting data from parent which is currently
the most desired use case.

Fix #14.

docs/features.rst

@@ -72,6 +72,13 @@ This nicely prevents unnecessary duplication. Redefining an
 attribute in a child object will by default overwrite value
 inherited from the parent.
 
+If inheriting data from parent is not desired in particular node
+of the tree it is possible to disable it using the following
+directive::
+
+    /:
+        inherit: false
+
 
 Merging
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

fmf/base.py

@@ -59,6 +59,9 @@ def __init__(self, data, name=None, parent=None):
         # (needed to prevent removing nodes with an empty dict).
         self._updated = False
 
+        # Special directives
+        self._directives = dict()
+
         # Store symlinks in while walking tree in grow() to detect
         # symlink loops
         if parent is None:
@@ -208,6 +211,33 @@ def _merge_special(self, data, source):
             else:
                 data[key] = value
 
+    def _process_directives(self, directives):
+        """ Check and process special fmf directives """
+
+        def check(value, type_, name=None):
+            """ Check for correct type """
+            if not isinstance(value, type_):
+                name = f" '{name}'" if name else ""
+                raise fmf.utils.FormatError(
+                    f"Invalid fmf directive{name} in '{self.name}': "
+                    f"Should be a '{type_.__name__}', "
+                    f"got a '{type(value).__name__}' instead.")
+
+        # Directives should be a directory
+        check(directives, dict)
+
+        # Check for proper values
+        for key, value in directives.items():
+            if key == "inherit":
+                check(value, bool, name="inherit")
+                continue
+            # No other directive supported
+            raise fmf.utils.FormatError(
+                f"Unknown fmf directive '{key}' in '{self.name}'.")
+
+        # Everything ok, store the directives
+        self._directives.update(directives)
+
     @staticmethod
     def init(path):
         """ Create metadata tree root under given path """
@@ -231,6 +261,9 @@ def merge(self, parent=None):
             parent = self.parent
         if parent is None:
             return
+        # Do not inherit when disabled
+        if self._directives.get("inherit") == False:
+            return
         self.sources = parent.sources + self.sources
         # Merge child data with parent data
         data = copy.deepcopy(parent.data)
@@ -257,6 +290,15 @@ def update(self, data):
         # Nothing to do if no data
         if data is None:
             return
+
+        # Handle fmf directives first
+        try:
+            directives = data.pop("/")
+            self._process_directives(directives)
+        except KeyError:
+            pass
+
+        # Process the metadata
         for key, value in sorted(data.items()):
             # Ensure there are no 'None' keys
             if key is None:

tests/core/inherit/data/.fmf/version

@@ -0,0 +1 @@
+1

tests/core/inherit/data/ci.fmf

@@ -0,0 +1,5 @@
+# Do not inherit common test metadata into CI configuration
+/:
+    inherit: false
+
+resultsdb-testcase: separate

tests/core/inherit/data/full/main.fmf

@@ -0,0 +1 @@
+summary: Full test

tests/core/inherit/data/main.fmf

@@ -0,0 +1,2 @@
+test: echo fine
+contact: somebody

tests/core/inherit/data/mini/main.fmf

@@ -0,0 +1 @@
+summary: Minimal test

tests/core/inherit/data/plans/features.fmf

@@ -0,0 +1,8 @@
+summary: This plan should inherit nothing
+
+provision:
+    how: local
+discover:
+    how: fmf
+execute:
+    how: tmt

tests/core/inherit/data/plans/main.fmf

@@ -0,0 +1,3 @@
+# Do not inherit common test metadata into plans
+/:
+    inherit: false

tests/core/inherit/invalid/.fmf/version

@@ -0,0 +1 @@
+1

tests/core/inherit/invalid/directive.fmf

@@ -0,0 +1 @@
+/: An invalid fmf directive

tests/core/inherit/main.fmf

@@ -0,0 +1,7 @@
+summary: Verify functionality of the `inherit` directive
+description:
+    Make sure that the inheritance from parent can be turned off
+    using the `inherit` directive both when defined in the same
+    file or separately. Test on a real-life scenario when plans
+    and the CI config are defined in the test namespace.
+require: [tmt]

tests/core/inherit/test.sh

@@ -0,0 +1,72 @@
+#!/bin/bash
+. /usr/share/beakerlib/beakerlib.sh || exit 1
+
+rlJournalStart
+    rlPhaseStartTest "Valid"
+        rlRun "pushd data"
+
+        # Check test
+        rlRun -s "fmf show --name /mini"
+        rlAssertGrep "Minimal test" $rlRun_LOG
+        rlAssertGrep "contact" $rlRun_LOG
+        rlAssertGrep "fine" $rlRun_LOG
+
+        # Check plan
+        rlRun -s "fmf show --name /plans/features"
+        rlAssertGrep "This plan should inherit nothing" $rlRun_LOG
+        rlAssertNotGrep "contact" $rlRun_LOG
+        rlAssertNotGrep "fine" $rlRun_LOG
+
+        # Check ci
+        rlRun -s "fmf show --name /ci"
+        rlAssertGrep "resultsdb-testcase: separate" $rlRun_LOG
+        rlAssertNotGrep "contact" $rlRun_LOG
+        rlAssertNotGrep "fine" $rlRun_LOG
+
+        rlRun "popd"
+    rlPhaseEnd
+
+    rlPhaseStartTest "Invalid"
+        rlRun "pushd $(mktemp -d)"
+        rlRun "fmf init"
+
+        # Directives should be dictionary
+        rlRun "echo '/: weird' > file.fmf"
+        rlRun -s "fmf show" 1
+        rlAssertGrep "Invalid fmf directive in '/file" $rlRun_LOG
+        rlAssertGrep "Should be a 'dict', got a 'str' instead." $rlRun_LOG
+
+        # Inherit should be a bool
+        rlRun "echo -e '/: \n    inherit: hmmm' > file.fmf"
+        rlRun -s "fmf show" 1
+        rlAssertGrep "Invalid fmf directive 'inherit'" $rlRun_LOG
+
+        # Unknown directive
+        rlRun "echo -e '/: \n    weird: hmmm' > file.fmf"
+        rlRun -s "fmf show" 1
+        rlAssertGrep "Unknown fmf directive 'weird' in '/file'" $rlRun_LOG
+
+        rlRun "popd"
+    rlPhaseEnd
+
+    rlPhaseStartTest "Integration with tmt"
+        rlRun "pushd data"
+
+        # Show tests
+        rlRun -s "tmt tests show"
+        rlAssertGrep "/mini" $rlRun_LOG
+        rlAssertGrep "Minimal test" $rlRun_LOG
+        rlAssertGrep "echo fine" $rlRun_LOG
+        rlAssertNotGrep "/plan" $rlRun_LOG
+        rlAssertNotGrep "/ci" $rlRun_LOG
+
+        # Check plan
+        rlRun -s "tmt plans show"
+        rlAssertGrep "/plan" $rlRun_LOG
+        rlAssertGrep "This plan should inherit nothing" $rlRun_LOG
+        rlAssertNotGrep "/test" $rlRun_LOG
+        rlAssertNotGrep "/ci" $rlRun_LOG
+
+        rlRun "popd"
+    rlPhaseEnd
+rlJournalEnd