Include line info for steps that raise exceptions

[philomates]

An attempt to help address #74

Given a flow that raises an exception, like:

(ns state-flow.scratch
  (:require [state-flow.core :as state-flow]
            [state-flow.cljtest :refer [match?]]
            [state-flow.state :as state]))

(defn inc-a [s]
  (update s :a inc))

(defn change-state-buggy []
  (state/modify inc-a))

(state-flow/run!
  (state-flow/flow "buggy flow"
                   (change-state-buggy)
                   (match? "never run" 1 2)))

the result used to be like the following, which doesn't help pinpoint that (change-state-buggy) is the offending step:

                state-flow.state/reify/fn       state.clj:   63
                 state-flow.scratch/inc-a     scratch.clj:    7
                      clojure.core/update        core.clj: 6196
                         clojure.core/inc        core.clj:  927
                                      ...
java.lang.NullPointerException:

Syntax error (ExceptionInfo) compiling at (state_flow/scratch.clj:12:1).
Flow "buggy flow (scratch.clj:13)" failed with exception

With the changes in this PR:

                state-flow.state/reify/fn       state.clj:   63
                 state-flow.scratch/inc-a     scratch.clj:    7
                      clojure.core/update        core.clj: 6196
                         clojure.core/inc        core.clj:  927
                                      ...
java.lang.NullPointerException:

Syntax error (ExceptionInfo) compiling at (state_flow/scratch.clj:12:1).
Flow "buggy flow (scratch.clj:13) -> (change-state-buggy) (line 14)" failed with exception

Note:

we don't have line metadata info for variable references, so

(state-flow/run!
  (state-flow/flow "buggy flow"
                   change-state-buggy))

results in

Syntax error (ExceptionInfo) compiling at (state_flow/scratch.clj:12:1).
Flow "buggy flow (scratch.clj:13) -> change-state-buggy" failed with exception

[philomates]

adding both the outer flow desc and the actual call sight info can be very useful. For example

(state-flow/run!
  (state-flow/flow "buggy flow"




                   (change-state-buggy)))

correctly shows

Syntax error (ExceptionInfo) compiling at (state_flow/scratch.clj:12:1).
Flow "buggy flow (line 13) -> `(change-stat...)` (line 18)" failed with exception

[sovelten]

You can also do (flow "my-buggy-flow" (change-state-buggy)) whenever you need for debugging purposes and you would get correct line numbering then.

It seems like a better trade off than a complicated solution just to provide line number tracking for primitive steps.

[caioaao]

This is a more contrived issue. I came across an interesting article about it, though, and might be a good direction to follow: https://pepeiborra.wordpress.com/2009/11/01/monadic-stack-traces-that-make-a-lot-of-sense/

I've only skimmed through the article, but the proposed solution is basically implementing an error monad that carries the stack trace

[philomates]

I've cleaned the implementation and it should be ready to review again

[sovelten]

Suggested change

	(defn annote-with-line-meta [flows]
	(defn annotate-with-line-meta [flows]

[gabrielgiussi]

If I run this I get

=> "level 1 (core_test.clj:2) -> (state-flow/current-description) (line 4)"

Where line 4 is coming from?

[gabrielgiussi]

I couldn't find any test when a flow is throwing an exception and the line is included. I guess we are testing current-description instead and probably we use current-description when an exception is caught but then are not relaying on internal impl details? 🤔

Shouldn't we have a test covering the case where an exception is raised and we have line information?

[philomates]

Thanks for the suggestion @gabrielgiussi, updated with a test