Support directory as input to linter

[julioz]

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Is your feature request related to a problem? Please describe.
The linter receives one or more proto files as input for execution. In our setup, we group all our proto files under a directory tree. The development experience would be better if we could pass the root directory name and the linter finds all proto files under its tree.

proto/
  - dir1/
    - api1.proto
    - api2.proto
  - dir2/
    - api3.proto
  - root.proto

As of now, passing proto/ as input to the linter, errors with:

2025/02/25 13:12:12 read proto: is a directory

Describe the solution you'd like
The linter walks through the file system, finds the proto files and executes the linting logic on all of them.

Describe alternatives you've considered
As of now we have to use a shell combination by piping the output of find into the linter executable.

[noahdietz]

Hey @julioz that's a cool idea and probably pretty easy to implement as you suggest. My guess as to why it wasn't implemented as such before is as you say, use find to script it, but also using a file descriptor set would be adequate as well.

If you are interested, feel free to open a PR. A function for walking a directory and collecting all of the .proto file paths as you say, followed by a check on the input paths to see execute this if one is a directory. I think we'd also want to dedupe all of the paths as well, to ensure a duplicate entry isn't accidentally provided e.g. api-linter proto/root.proto proto.