File size increase in 6.4.3 when using dynamic_context

[davidszotten]

Describe the bug
Hi. I suspect this is related to #1538, hence the similar name, but this is a different aspect. My symptom is a huge increase in coverage data file size (~4 -> 200Mb)

To Reproduce
I made a test project with 3 pytest files ,each with a single empty test, and added dynamic_context = test_function to a coveragerc

running pytest under coverage and then reading the line_bits table, i get
(coverage run -m pytest tests/ ; sqlite3 .coverage 'select path, context from line_bits join file on file_id = file.id join context on context_id = context.id')

on 6.4.2

tests/test_1.py|
tests/test_1.py|test_1.test1
tests/test_2.py|
tests/test_2.py|test_2.test2
tests/test_3.py|
tests/test_3.py|test_3.test3

on 6.4.3

tests/test_1.py|
tests/test_1.py|test_1.test1
tests/test_1.py|test_2.test2
tests/test_1.py|test_3.test3
tests/test_2.py|
tests/test_2.py|test_1.test1
tests/test_2.py|test_2.test2
tests/test_2.py|test_3.test3
tests/test_3.py|
tests/test_3.py|test_1.test1
tests/test_3.py|test_2.test2
tests/test_3.py|test_3.test3

It looks like there is now a line for every file for every context.

Is this expected? Avoidable? The fix for #1538 seems to focus on queries. does that mean we can't avoid storing the extra data in the first place?

[nedbat]

Can you share the code for your test project?

[davidszotten]

sure. https://github.com/davidszotten/coverage-file-size

[davidszotten]

i might be missing a bunch of context/knowledge, but from what i can tell, while f54428f fixes the issue on top of 6.4.2 through 7.0.5, as of 7.10.0, at least the example from cython still passes after reverting f54428f

[davidszotten]

was 4cc32922685c6#diff-e5185ca855df54af4f94c983f99b52cfad9ddc17386353d09acdfa994dd72a33L574-L579 an alternative (and better) fix for the cython issue than adding lots of empty file-context entries?

[andersk]

@davidszotten My testing agrees, so we can revert f54428f:

• Revert "Map also empty dictionaries to file" #1629