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Clarify output when printing nested exception traces
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Since v10.2.0, if an exception has a nested cause exception, the cause is also
displayed in the trace output.[1]

For heavily-nested exceptions, this output can be quite lengthy - for example,
Rails migrations nest DB errors twice over, resulting in an error message and
backtrace repeated three times.

To break up this output and make it clearer what each individual backtrace
relates to, this adds whitespace and a "Caused by:" label to each nested
exception being displayed.

To prevent "Caused by:" labels occurring on their own, I've moved the
exception loop shortcut return into the `#display_cause_details` method. This
doesn't alter the behaviour of the shortcut, as only the first exception will
be unconditionally printed (which was already the case, as the first exception
can't be already seen).

[1] fbb22e7
[2] 57c932c
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Simon Coffey committed Oct 19, 2017
1 parent 99f48f2 commit f7774e8
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Showing 2 changed files with 14 additions and 4 deletions.
17 changes: 13 additions & 4 deletions lib/rake/application.rb
Original file line number Diff line number Diff line change
Expand Up @@ -207,13 +207,22 @@ def display_error_message(ex) # :nodoc:
end

def display_exception_details(ex) # :nodoc:
seen = Thread.current[:rake_display_exception_details_seen] ||= []
return if seen.include? ex
seen << ex
display_exception_details_seen << ex

display_exception_message_details(ex)
display_exception_backtrace(ex)
display_exception_details(ex.cause) if has_cause?(ex)
display_cause_details(ex.cause) if has_cause?(ex)
end

def display_cause_details(ex) # :nodoc:
return if display_exception_details_seen.include? ex

trace "\nCaused by:"
display_exception_details(ex)
end

def display_exception_details_seen # :nodoc:
Thread.current[:rake_display_exception_details_seen] ||= []
end

def has_cause?(ex) # :nodoc:
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1 change: 1 addition & 0 deletions test/test_rake_application.rb
Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,7 @@ def test_display_exception_details_cause

assert_empty out

assert_match "Caused by:", err
assert_match "cause a", err
assert_match "cause b", err
end
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