Fail tests when schema has changes

Author: chinedufn

crates/cli-support/src/wit/mod.rs

@@ -1459,11 +1459,11 @@ fn extract_programs<'a>(
 it looks like the Rust project used to create this wasm file was linked against
 version of wasm-bindgen that uses a different bindgen format than this binary:
 
-  rust wasm file: {}
-     this binary: {}
+  rust wasm file schema version: {}
+     this binary schema version: {}
 
 Currently the bindgen format is unstable enough that these two schema versions
-must exactly match. You can accomplish ths by either updating the wasm-bindgen
+must exactly match. You can accomplish this by either updating the wasm-bindgen
 dependency or this binary.
 
 You should be able to update the wasm-bindgen dependency with:

crates/shared/build.rs

@@ -27,5 +27,5 @@ fn set_schema_version_env_var() {
     let mut hasher = DefaultHasher::new();
     hasher.write(&schema_file);
 
-    println!("cargo:rustc-env=SCHEMA_VERSION={}", hasher.finish());
+    println!("cargo:rustc-env=SCHEMA_FILE_HASH={}", hasher.finish());
 }

crates/shared/src/lib.rs

@@ -1,8 +1,9 @@
 #![doc(html_root_url = "https://docs.rs/wasm-bindgen-shared/0.2")]
 
-// The schema is so unstable right now we just force it to change whenever this
-// file changes.
-pub const SCHEMA_VERSION: &str = env!("SCHEMA_VERSION");
+// This gets changed whenever our schema changes.
+// At this time versions of wasm-bindgen and wasm-bindgen-cli are required to have the exact same
+// SCHEMA_VERSION in order to work together.
+pub const SCHEMA_VERSION: &str = "0.2.74";
 
 #[macro_export]
 macro_rules! shared_api {
@@ -191,3 +192,25 @@ pub fn version() -> String {
     }
     return v;
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Whenever this file changes, the SCHEMA_FILE_HASH environment variable will change and the
+    // schema_version test below will fail.
+    // Proceed as follows:
+    //
+    // If the schema in this library has changed then:
+    //  1. Change this APPROVED_SCHEMA_FILE_HASH to the new hash.
+    //
+    // If the schema in this library has changed then:
+    //  1. Bump the version in `crates/shared/Cargo.toml`
+    //  2. Change the `SCHEMA_VERSION` in this library to this new Cargo.toml version
+    const APPROVED_SCHEMA_FILE_HASH: &'static str = "12345";
+
+    #[test]
+    fn schema_version() {
+        assert_eq!(env!("SCHEMA_FILE_HASH"), APPROVED_SCHEMA_FILE_HASH)
+    }
+}