Name conflict when a struct is called "Context"

[dbrgn]

As discussed in #1242: I'm getting the following error when a struct is called Context when calling wasm-pack test --headless --firefox:

  [3/6] Compiling tests to WASM...
     Compiling compose-area v0.1.0 (/home/danilo/Projects/compose-area)
  error: linking with `rust-lld` failed: exit code: 1
    |
    = note: "rust-lld" "-flavor" "wasm" "--no-threads" "-z" "stack-size=1048576" "--stack-first" "--allow-undefined" "--no-entry" "--fatal-warnings" "--export-dynamic" "--no-
    = note: rust-lld: error: duplicate symbol: __wbg_context_free
            >>> defined in /home/danilo/Projects/compose-area/target/wasm32-unknown-unknown/debug/deps/libcompose_area.rlib(compose_area.1zjlr9g8cstvtdrr.rcgu.o)
            >>> defined in /home/danilo/Projects/compose-area/target/wasm32-unknown-unknown/debug/deps/libwasm_bindgen_test-258015b5016fb118.rlib(wasm_bindgen_test-258015b501

Probably a name mangling issue.

[alexcrichton]

Thanks again for spinning this off!

This is actually somewhat difficult to support now that I think about it. Right now all the exports from Rust are generated into a flat namespace in JS, so this is actually a legitimate namespace conflict. I'm not sure we can really support duplicate-ly named types in separate crates being linked together because we wouldn't know what to call the names in JS!

What I do think, however, is that the test framework should be using less common names :)

[dbrgn]

Do we have access to the source crate of a symbol? Maybe that could be integrated into the name?

[alexcrichton]

We do! All that would end up with though is a better error message here, which is certainly an improvement! I'm nto sure we could actually allow this still

[alexcrichton]

I've posted a rename for our own Context in #1280

[dbrgn]

Thank you!

Feel free to close this issue, unless it should stay open to discuss further namespacing / name mangling.

[alexcrichton]

Ok I think in that case I'll go ahead and close

[dimitri-lenkov]

Thank you so much for this comment --- it got me unstuck.

I found this issue when looking up "wasm_bindgen duplicate symbol".

In my particular case, I have multiple crates in a cargo workspace that followed similar strut & method naming patterns, e.g. both workspace crates "foo" and "bar" had structs with names and methods like this:

impl Consume {
   //  . . .

   #[wasm_bindgen]
   pub fn start(/* ... */) {}
}

and the solution was to re-name the structs to be "crate specific", e.g. FooConsume and BarConsume respectively. By doing this, the generated symbol names would be *_foo_consume_start & *_bar_consume_start instead of the duplicate-ly generated name *_consume_start.

---

I'm not sure we can really support duplicate-ly named types in separate crates being linked together because we wouldn't know what to call the names in JS!

As a complete noob: Is it possible for #[wasm_bindgen] to automatically shove-in the current crate's name into the link_name to help "mangle" the name a bit more? wasm_bindgen is still sort of voo-doo magic for me lol.