test: simplify the metacov flow a bit

- default COVERAGE_METAFILE=.metacov for convenience

- don't make json and xml reports, if we need them we'll do it
  explicitly.

Author: nedbat

.github/workflows/coverage.yml

@@ -123,7 +123,6 @@ jobs:
         id: combine
         env:
           COVERAGE_RCFILE: "metacov.ini"
-          COVERAGE_METAFILE: ".metacov"
           COVERAGE_CONTEXT: "yes"
         run: |
           set -xe

igor.py

@@ -210,18 +210,15 @@ def run_tests_with_coverage(tracer, *runner_args):
 
 
 def do_combine_html():
-    """Combine data from a meta-coverage run, and make the HTML and XML reports."""
+    """Combine data from a meta-coverage run, and make the HTML report."""
     import coverage
     os.environ['COVERAGE_HOME'] = os.getcwd()
-    os.environ['COVERAGE_METAFILE'] = os.path.abspath(".metacov")
     cov = coverage.Coverage(config_file="metacov.ini")
     cov.load()
     cov.combine()
     cov.save()
     show_contexts = bool(os.environ.get('COVERAGE_DYNCTX') or os.environ.get('COVERAGE_CONTEXT'))
     cov.html_report(show_contexts=show_contexts)
-    cov.xml_report()
-    cov.json_report(pretty_print=True)
 
 
 def do_test_with_tracer(tracer, *runner_args):

metacov.ini

@@ -8,7 +8,7 @@
 
 [run]
 branch = true
-data_file = ${COVERAGE_METAFILE?}
+data_file = ${COVERAGE_METAFILE-.metacov}
 parallel = true
 relative_files = true
 source =
@@ -20,7 +20,7 @@ dynamic_context = ${COVERAGE_DYNCTX-none}
 context = ${COVERAGE_CONTEXT-none}
 
 [report]
-# We set a different pragmas so our code won't be confused with test code, and
+# We set different pragmas so our code won't be confused with test code, and
 # we use different pragmas for different reasons that the lines won't be
 # measured.
 exclude_lines =