When dbt encounters two sources with the same name, it crashes with an exception

[beckjake]

Describe the bug

When dbt hits a duplicate source, it crashes with a bad error about 'UnpatchedSourceDefinition' object has no attribute 'source_name'.

Steps To Reproduce

1. Define a source and a table
2. Define the table a second time (either in a new source with the same name or a second table in the original source)
3. dbt compile.

version: 2
sources:
 - name: my_source
   tables:
    - name: foo
    - name: foo

Expected behavior

I should get this error:

  dbt found two resources with the name "my_source_foo". Since these resources have the same name,
  dbt will be unable to find the correct resource when source("my_source", "foo") is used. To fix this,
  change the name of one of these resources:
  - source.minimal.my_source.foo (models/schema.yml)
  - source.minimal.my_source.foo (models/schema.yml)

This happens on any db, any python, dbt 0.17.0rc1

[beckjake]

Fixed in #2464