Add relation name to the exception in case of archive failure

Fixes dbt-labs#1066

dbt/exceptions.py

@@ -380,9 +380,10 @@ def missing_config(model, name):
 
 
 def missing_relation(relation, model=None):
-    raise_compiler_error(
-        "Relation {} not found!".format(relation),
-        model)
+    base_msg = ('The relation`{relation}` was not found!\n'
+                'Check that the relation exists, and that your user'
+                ' has permissions to select from this relation.')
+    raise_compiler_error(base_msg.format(relation=relation), model)
 
 
 def relation_wrong_type(relation, expected_type, model=None):

dbt/include/global_project/macros/materializations/archive/archive.sql

@@ -174,7 +174,8 @@
       identifier=target_table) -%}
 
   {%- if source_relation is none -%}
-    {{ exceptions.missing_relation(source_relation) }}
+    {%- set source_relation_name = [source_schema, source_table]|join(".") -%}
+    {{ exceptions.missing_relation(source_relation_name)}}
   {%- endif -%}
 
   {%- if target_relation is none -%}