_variables: Fix reporting of missing variable

When the missing variable was not defined, we would get an exception
as a string doesn't contain provenance information.

- Add a test to prevent regression

3 files changed, 8 insertions, 3 deletions

diff --git a/src/buildstream/_variables.pyx b/src/buildstream/_variables.pyx
index 470feddc9..8f91c9ced 100644
--- a/src/buildstream/_variables.pyx
+++ b/src/buildstream/_variables.pyx
@@ -139,7 +139,7 @@ cdef class Variables:
             for var in expstr[1::2]:
                 if var not in self._expstr_map:
                     line = "  unresolved variable '{unmatched}' in declaration of '{variable}' at: {provenance}"
-                    provenance = expstr.get_provenance()
+                    provenance = self.original.get_scalar(key).get_provenance()
                     summary.append(line.format(unmatched=var, variable=key, provenance=provenance))
         if summary:
             raise LoadError(LoadErrorReason.UNRESOLVED_VARIABLE,
diff --git a/tests/format/variables.py b/tests/format/variables.py
index 93814279a..4610e039f 100644
--- a/tests/format/variables.py
+++ b/tests/format/variables.py
@@ -78,11 +78,12 @@ def test_overrides(cli, datafiles, target, varname, expected):
     assert result_vars.get_str(varname) == expected
 
 
+@pytest.mark.parametrize("element", ["manual.bst", "manual2.bst"])
 @pytest.mark.datafiles(os.path.join(DATA_DIR, 'missing_variables'))
-def test_missing_variable(cli, datafiles):
+def test_missing_variable(cli, datafiles, element):
     project = str(datafiles)
     result = cli.run(project=project, silent=True, args=[
-        'show', '--deps', 'none', '--format', '%{config}', 'manual.bst'
+        'show', '--deps', 'none', '--format', '%{config}', element
     ])
     result.assert_main_error(ErrorDomain.LOAD,
                              LoadErrorReason.UNRESOLVED_VARIABLE)
diff --git a/tests/format/variables/missing_variables/manual2.bst b/tests/format/variables/missing_variables/manual2.bst
new file mode 100644
index 000000000..bd8e2baf7
--- /dev/null
+++ b/tests/format/variables/missing_variables/manual2.bst
@@ -0,0 +1,4 @@
+kind: manual
+
+variables:
+  test: hello %{missing}