smithy4sWildcardArgument in generated-metadata.smithy causes conflicts

[zkerriga]

Problem

Compile / smithy4sWildcardArgument is a per-project build setting derived from scalaVersion and scalacOptions.
The sbt plugin hands it to codegen by writing a synthetic file generated-metadata.smithy.

Smithy rejects conflicting values of this metadata.
The result: two libraries that differ only in their own scalac options become incompatible for any downstream smithy4s consumer.

Reproduction

project/build.properties

sbt.version = 1.9.9

project/plugins.sbt

addSbtPlugin("com.disneystreaming.smithy4s" % "smithy4s-sbt-codegen" % "0.19.11")

build.sbt

ThisBuild / scalaVersion := "2.13.16"

// derives smithy4sWildcardArgument = "_"
lazy val libA = project
  .enablePlugins(Smithy4sCodegenPlugin)

// same plugin, same Scala version; derives "?"
lazy val libB = project
  .enablePlugins(Smithy4sCodegenPlugin)
  .settings(
    addCompilerPlugin("org.typelevel" %% "kind-projector" % "0.13.4" cross CrossVersion.full),
    scalacOptions += "-P:kind-projector:underscore-placeholders",
  )

lazy val app = project
  .enablePlugins(Smithy4sCodegenPlugin)
  .dependsOn(libA, libB)

then sbt compile fails with:

[error] (app / Compile / smithy4sCodegen) software.amazon.smithy.model.validation.ValidatedResultException:
Result contained ERROR severity validation events:
[ERROR] -: Metadata conflict for key `smithy4sWildcardArgument`. Defined in both
  `jar:file:///.../libB/target/scala-2.13/libb_2.13-0.1.0.jar!/META-INF/smithy/generated-metadata.smithy [2, 37]`
  and
  `jar:file:///.../libA/target/scala-2.13/liba_2.13-0.1.0.jar!/META-INF/smithy/generated-metadata.smithy [2, 37]`

which is unexpected, because without Smithy, such a module and options structure would compile and be ok.

I couldn't find an easy fix for that, and I see generated-metadata.smithy being mentioned in tests. Is there any important reason for such behavior?

[snevevo]

Also encountered this issue. It's worth mentioning that the generation would fail even if the modules have identical values of smithy4sWildcardArgument.

So even if you consume same-scala-version libraries you are in trouble