Main branch does not compile for some versions of locally-installed flatc

[stephanemagnenat]

Fetching a fresh main branch:
git clone git@github.com:planus-org/planus.git

And compiling it:
cd planus && cargo build

Leads to the following errors:

   Compiling rust-test v0.4.0 (/home/steph/test/planus/test/rust)
error[E0405]: cannot find trait `SafeSliceAccess` in crate `flatbuffers`
  --> /home/steph/test/planus/target/debug/build/rust-test-c32ec9e90a91632a/out/planus_test/alignment_generated.rs:29:19
   |
29 | impl flatbuffers::SafeSliceAccess for NoAlign {}
   |                   ^^^^^^^^^^^^^^^ not found in `flatbuffers`

error[E0405]: cannot find trait `SafeSliceAccess` in crate `flatbuffers`
   --> /home/steph/test/planus/target/debug/build/rust-test-c32ec9e90a91632a/out/planus_test/alignment_generated.rs:129:19
    |
129 | impl flatbuffers::SafeSliceAccess for Align4 {}
    |                   ^^^^^^^^^^^^^^^ not found in `flatbuffers`

error[E0405]: cannot find trait `SafeSliceAccess` in crate `flatbuffers`
   --> /home/steph/test/planus/target/debug/build/rust-test-c32ec9e90a91632a/out/planus_test/alignment_generated.rs:229:19
    |
229 | impl flatbuffers::SafeSliceAccess for Align16 {}
    |                   ^^^^^^^^^^^^^^^ not found in `flatbuffers`

error[E0405]: cannot find trait `SafeSliceAccess` in crate `flatbuffers`
   --> /home/steph/test/planus/target/debug/build/rust-test-c32ec9e90a91632a/out/planus_test/alignment_generated.rs:332:19
    |
332 | impl flatbuffers::SafeSliceAccess for AlignmentStruct {}
    |                   ^^^^^^^^^^^^^^^ not found in `flatbuffers`

For more information about this error, try `rustc --explain E0405`.
error: could not compile `rust-test` (lib) due to 4 previous errors

I assume that this is due to some changes on the google flatbuffers library side.

[TethysSvensson]

This happens because we use flatbuffers in our testing, to make sure that we are compatible. We will use the locally installed flatc, which might or might not be compatible with the flatbuffers crate we depend on.

Perhaps we should add some debugging to our test to make it more clear when this happens?

Can you tell me the output of flatc --version? On my machine this says flatc version 22.11.23, and cargo build does work as expected.

[stephanemagnenat]

Thanks for the answer! I am indeed using an old version of flatc (2.0.6) for legacy reasons on our side. I'm happy to close the issue then.

Yet, maybe it would be helpful to add a check of flatc for compatibility? As far as I know, it is uncommon in the Rust world that successfully building a project depends on the version of a locally-installed third-party tool.

[TethysSvensson]

I think you have a point, and perhaps we should fix that as well.

The reason why we haven't currently done it like that, is that we only use the third-party tool for testing, and writing the code to get it installed through build.rs is surprisingly difficult. We would at least require a locally installed cmake, and I am not sure I see the benefit to doing that.

For now what you can do is run cargo build -p planus-cli to avoid compiling the tests.