Better error message when running wasm-pack in a non-crate directory

src/manifest.rs

@@ -68,6 +68,12 @@ struct Repository {
 
 fn read_cargo_toml(path: &Path) -> Result<CargoManifest, Error> {
     let manifest_path = path.join("Cargo.toml");
+    if !manifest_path.is_file() {
+        return Error::crate_config(&format!(
+            "Crate directory is missing a `Cargo.toml` file; is `{}` the wrong directory?",
+            path.display()
+        )).map(|_| unreachable!());
+    }
     let mut cargo_file = File::open(manifest_path)?;
     let mut cargo_contents = String::new();
     cargo_file.read_to_string(&mut cargo_contents)?;

tests/all/build.rs

@@ -11,8 +11,11 @@ fn build_in_non_crate_directory_doesnt_panic() {
         &fixture.path.display().to_string(),
     ]).unwrap();
     let logger = logger::new(&cli.cmd, cli.verbosity).unwrap();
+    let result = command::run_wasm_pack(cli.cmd, &logger);
     assert!(
-        command::run_wasm_pack(cli.cmd, &logger).is_err(),
+        result.is_err(),
         "running wasm-pack in a non-crate directory should fail, but it should not panic"
     );
+    let err_msg = result.unwrap_err().to_string();
+    assert!(err_msg.contains("missing a `Cargo.toml`"));
 }