fix: helpful error messages when runtime mismatch for build

Author: sriram-mv

aws_lambda_builders/exceptions.py

@@ -16,8 +16,11 @@ class UnsupportedManifestError(LambdaBuilderError):
 
 
 class MisMatchRuntimeError(LambdaBuilderError):
-    MESSAGE = "A runtime version mismatch was found for the given language " \
-              "'{language}', required runtime '{required_runtime}'"
+    MESSAGE = "{language} executable found in your path does not " \
+              "match runtime. " \
+              "\n Expected version: {required_runtime}, Found version: {found_runtime}. " \
+              "\n Consider moving {required_runtime} up path hierarchy." \
+              "\n Possibly related: https://github.com/awslabs/aws-lambda-builders/issues/30"
 
 
 class WorkflowNotFoundError(LambdaBuilderError):

aws_lambda_builders/validate.py

@@ -17,6 +17,7 @@ def validate_python_cmd(required_language, required_runtime_version):
         "python",
         "-c",
         "import sys; "
+        "sys.stdout.write('python' + str(sys.version_info.major) + '.' + str(sys.version_info.minor)); "
         "assert sys.version_info.major == {major} "
         "and sys.version_info.minor == {minor}".format(
             major=major,
@@ -63,10 +64,11 @@ def validate_runtime(cls, required_language, required_runtime):
             p = subprocess.Popen(cmd,
                                  cwd=os.getcwd(),
                                  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-            p.communicate()
+            found_runtime, _ = p.communicate()
             if p.returncode != 0:
                 raise MisMatchRuntimeError(language=required_language,
-                                           required_runtime=required_runtime)
+                                           required_runtime=required_runtime,
+                                           found_runtime=str(found_runtime.decode('utf-8')))
         else:
             LOG.warning("'%s' runtime has not "
                         "been validated!", required_language)

tests/unit/test_runtime.py

@@ -13,7 +13,7 @@ def __init__(self, returncode):
         self.returncode = returncode
 
     def communicate(self):
-        pass
+        return b'python3,6', None
 
 
 class TestRuntime(TestCase):
@@ -44,6 +44,7 @@ def test_runtime_validate_mismatch_version_runtime(self):
 
     def test_python_command(self):
         cmd = validate_python_cmd("python", "python2.7")
-        version_strings = ["sys.version_info.major == 2", "sys.version_info.minor == 7"]
+        version_strings = ["sys.stdout.write", "sys.version_info.major == 2",
+                           "sys.version_info.minor == 7"]
         for version_string in version_strings:
             self.assertTrue(any([part for part in cmd if version_string in part]))