elog-gen: allow inherits from errors without meta

Previously, elog-gen only support inherits from errors that have meta,
and if we inherit from an error without meta, e.g.
Common.InternalFailure, we get build error like:

    KeyError: 'xyz.openbmc_project.Common.InternalFailure'

This commit makes elog-gen to allow such case, so it is possible to
allow a base error without meta, and inheriting error with additional
error, e.g.

    # In Common:
    - name: NotAllowed  ## No meta

    # In Time:
    - name: NotAllowed
      inherits:
        - xyz.openbmc_project.Common.NotAllowed
      meta:
        - str: "OWNER=%s"
          type: string
        - str: "SYNC_METHOD=%s"
          type: string

Note: the "inherit" here does not mean the the error inherits from
base errors in c++ class, it just makes error "logically" inherits base
errors. And in future commits we could make it "really" inherits base
errors in c++ level.

Tested: Verify phosphor-logging builds correctly with above example
        error interfaces, and service is able to use such errors with
        elog.

Change-Id: I8dccd7112881e3eb77a8f6ec62a532062348d2ef
Signed-off-by: Lei YU <mine260309@gmail.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/tools/phosphor-logging/templates/elog-gen-template.mako.hpp b/tools/phosphor-logging/templates/elog-gen-template.mako.hpp
index 23d8c08..0d156ad 100644
--- a/tools/phosphor-logging/templates/elog-gen-template.mako.hpp
+++ b/tools/phosphor-logging/templates/elog-gen-template.mako.hpp
@@ -103,10 +103,13 @@ struct ${b}
         parent_meta += [parent_namespace + "::" + parent_name + "::" +
                         p for p in meta[parent]]
         parent_meta_short = ', '.join(meta[parent])
-        if(meta_string):
-            meta_string = meta_string + ", " + parent_meta_short
-        else:
-            meta_string = parent_meta_short
+        # The parent may have empty meta,
+        # so only add parent meta when it exists
+        if (parent_meta_short):
+            if(meta_string):
+                meta_string = meta_string + ", " + parent_meta_short
+            else:
+                meta_string = parent_meta_short
         parent = parents[parent]
 
     if example_yaml: