I have tried to make this as minimally invasive as possible and hopefully the naming is within project style.

Please take a look.

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Commit Messages

• Most changes should be accompanied by tests.
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Add AST node IDs to types.Err for errorable expressions

Currently, it is not possible to obtain the source location of a runtime
error making it difficult sometimes to identify the cause of an issue.
If an AST node ID is available, the source location can be obtained, so
add this information to runtime errors.

ref.Val values returned by the following types are examined for error
state and if an error and no AST node has been set, the node ID of the
Interpretable is added to the error.

* evalAnd
* evalAttr
* evalBinary
* evalExhaustiveConditional
* evalList
* evalMap
* evalMap
* evalObj
* evalOr
* evalTestOnly
* evalUnary
* evalVarArgs
* evalWatchAttrQual
* evalWatchConstQual
* evalWatchQual
* evalZeroArity

Reviews

• Perform a self-review. ✔️
• Make sure the Travis CI build passes. ✔️
• Assign a reviewer once both the above have been completed.

Merging

• If a CEL maintaner approves the change, it may be merged by the author if
  they have write access. Otherwise, the change will be merged by a maintainer.
• Multiple commits should be squashed before merging.
• Please append the line closes #<issue-num>: description in the merge message,
  if applicable.