[infra] Print additional information for build/coverage failures on GCB (#3104). (#3208)

* [infra] Explicily print failing build config in the GCB log (#3104).

* add trailing "false" command + add a message for misisng coprus backups in code coverage build

* improve the coverage message and behavior

* fix exit command

* use .format() for a single argument format string too

* fix typo

infra/gcb/build_and_run_coverage.py

@@ -176,7 +176,14 @@ def get_build_steps(project_dir):
           'args': [
               'bash',
               '-c',
-              'for f in /corpus/*.zip; do unzip -q $f -d ${f%%.*}; done && coverage',
+              ('for f in /corpus/*.zip; do unzip -q $f -d ${f%%.*} || '
+               'echo "Failed to unpack the corpus for $(basename ${f%%.*}). '
+               'This usually means that corpus backup for a particular fuzz '
+               'target does not exist. If a fuzz target was added in the last '
+               '24 hours, please wait one more day. Otherwise, something is '
+               'wrong with the fuzz target or the infrastructure, and corpus '
+               'pruning task does not finish successfully." && exit 1; '
+               'done && coverage')
           ],
           'volumes': [{'name': 'corpus', 'path': '/corpus'}],
       }

infra/gcb/build_project.py

@@ -236,6 +236,8 @@ def get_build_steps(project_dir):
         if not workdir:
           workdir = '/src'
 
+        failure_msg = ('FAILED IN THE FOLLOWING CONFIG: --sanitizer {0} '
+                       '--engine {1}').format(sanitizer, fuzzing_engine)
         build_steps.append(
             # compile
             {
@@ -251,8 +253,9 @@ def get_build_steps(project_dir):
                     # `cd /src && cd {workdir}` (where {workdir} is parsed from
                     # the Dockerfile). Container Builder overrides our workdir
                     # so we need to add this step to set it back.
-                    'rm -r /out && cd /src && cd {1} && mkdir -p {0} && compile'
-                    .format(out, workdir),
+                    ('rm -r /out && cd /src && cd {1} && mkdir -p {0} && '
+                     'compile || echo "build_fuzzers {2}" && false')
+                    .format(out, workdir, failure_msg),
                 ],
             })
 
@@ -276,7 +279,12 @@ def get_build_steps(project_dir):
               {
                   'name': 'gcr.io/oss-fuzz-base/base-runner',
                   'env': env,
-                  'args': ['bash', '-c', 'test_all'],
+                  'args': [
+                      'bash',
+                      '-c',
+                      'test_all || echo "check_build {0}" && false'.format(
+                          failure_msg)
+                  ],
               })
 
         if project_yaml['labels']: