Currently a number of the subcommands of go tool covdata (textfmt, percent, ...) require users to pass the-i argument which specifies the input dirs to examine (comma separated) for coverage data. Only the files in the named directory/directories are examined, and no subdirectories are visited. This lack of subdirectory traversal leads to some (admittedly minor) inconveniences for users of this command.

Example 1: Multiple static locations, unchanging

/ coveragedata 
    / unittests
        <coverage files from the unit test suite go here>
    / integrationtests
        <coverage files from the integration test suite go here>

Users may want to examine the unit test coverage (go tool covdata func -i=coveragedata/unittests), the integration test coverage (go tool covdata func -i=coveragedata/integrationtests), or the combined coverage. Today, getting the combined coverage requires either manually specifying both directories as part of the func subcommand (go tool covdata func -i=coveragedata/unittests,coveragedata/integrationtests), or by manually specifying both directories as part of the merge subcommand (go tool covdata merge -i=coveragedata/unittests,coveragedata/integrationtests -o merged) and then later running the func command on the merged result (go tool covdata func -i=merged).

It would be easier to allow for -i to traverse the passed directories (including any subdirectories), such that users wishing to view coverage data for both could simply run go tool covdata func -i=coveragedata or go tool covdata merge -i=coveragedata -o merged && go tool covdata func -i=merged. However, for two static directory locations which don't change, this represents a very minor papercut and can easily be worked around with existing options.

Example 2: Multiple static locations, changing

/ coveragedata 
    / windows
    / macos
    / linux 
    ... 

The testing coverage docs specifically reference an example of:

For example, consider a program that runs on both macOS and on Windows. The author of this program might want to combine coverage profiles from separate runs on each operating system into a single profile corpus, so as to produce a cross-platform coverage summary.

In practice, this could become a bit unwieldily, as the every time a new platform is added for testing the call to the covdata command would have to be updated to manually pass in this new directory location. Updating the coverage command may be forgotten, silently missing being included in top level coverage. If directory traversal was included, this command could again be simplified to go tool covdata func -i=coveragedata eliminating the risk of new platforms being missed. Again, the current tools provide the necessary workaround (-i=coveragedata/windows,coveragedata/macos, ...), and the behavior still remains a minor papercut.

Example 3: Dynamic Locations

/ coveragedata 
    / us-windows-paypal
    / us-macos-stripe
    / ca-windows-paypal
    / ca-macos-stripe
    / es-windows-paypal
    / es-macos-stripe
    ... 

Consider a hypothetical company which handles user purchases which wants to run its integration test suite for a number of countries (EN / CA / ES / ...), platforms (windows, macos, ...), and payment vendors (paypal, stripe, ...) to measure overall coverage for all supported combinations of purchase flows. This generates a dynamic number of directory locations, which all need to be fed into the -i argument. This can certainly be accomplished with the current tooling, but would likely be much simpler (and less error-prone) if they could just specify go tool covdata func -i=coveragedata and avoid having to dynamically build a list of every possible directory location.

The proposed change would be to update this to instead call filepath.WalkDir , with no other changes to the parsing logic.