Using this guide to integrate try-runtime on my node i get the error about get random not building for wasm.

  error: the wasm32-unknown-unknown target is not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
     --> /home/simson/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.3/src/lib.rs:219:9
  219 | /         compile_error!("the wasm32-unknown-unknown target is not supported by \
  220 | |                         default, you may need to enable the \"js\" feature. \
  221 | |                         For more information see: \
  222 | |                         https://docs.rs/getrandom/#webassembly-support");
      | |________________________________________________________________________^

  error[E0433]: failed to resolve: use of undeclared crate or module `imp`
     --> /home/simson/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.3/src/lib.rs:246:5
  246 |     imp::getrandom_inner(dest)
      |     ^^^ use of undeclared crate or module `imp`

I get this error when I enable frame-try-runtime on the second line below (In [features] section of runtime/Cargo.toml)

try-runtime = [

I suspect the root cause of this is not related to wasm but rather that some dependency is leaking std code into the wasm build. What kind of miss-configuration should I be looking for to find this problem?

  • Did you make sure to make try-runtime optional and enable it with std? Can you share a diff of the changes you made to your node leading to this error?
    – Shawn Tabrizi
    Feb 9, 2022 at 7:41
  • I will try to boil it down to a minimal reproducible error, hold on
    – Simson
    Feb 10, 2022 at 0:58

1 Answer 1


It looks like the latest Rust nightly has broken our Wasm builds.

There have been other reports of this issue here:


And the fix is coming in here:


  • No it can't be the tool chain, I can build the same sha withou the changes but this: looks like the problem sudipghimire533 commented 10 days ago Usually this is due to missing some entry features section like [features] std = [ 'sp-std/std', # if some crate entry is missing here ] Or you might be missing default-features = false in some toml file Straight-forward way to resolve this would be compare the commit where everything was fine and carefully analyse the changes in all Cargo.toml file keeping in mind above-mentioned 2 things.
    – Simson
    Feb 11, 2022 at 1:15

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