From 1a2ecccbebb7e0aab8b292874c75734c5d058728 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Tue, 7 Apr 2020 12:05:28 -0500
Subject: [PATCH] Make too many imports an instantiation error (#1478)

* Make too many imports an instantiation error

Previously we'd accidentally only take the head of the list when
instantiating, but instead this changes the API to require exactly the
right number of imports.
---
 crates/api/src/instance.rs   |  8 ++++++++
 crates/api/tests/instance.rs | 13 +++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 crates/api/tests/instance.rs

diff --git a/crates/api/src/instance.rs b/crates/api/src/instance.rs
index 391754c42b52..d60c3d17f90c 100644
--- a/crates/api/src/instance.rs
+++ b/crates/api/src/instance.rs
@@ -124,6 +124,14 @@ impl Instance {
             }
         }
 
+        if imports.len() != module.imports().len() {
+            bail!(
+                "wrong number of imports provided, {} != {}",
+                imports.len(),
+                module.imports().len()
+            );
+        }
+
         module.register_frame_info();
         let config = store.engine().config();
         let instance_handle = instantiate(
diff --git a/crates/api/tests/instance.rs b/crates/api/tests/instance.rs
new file mode 100644
index 000000000000..c0f3db86a296
--- /dev/null
+++ b/crates/api/tests/instance.rs
@@ -0,0 +1,13 @@
+use anyhow::Result;
+use wasmtime::*;
+
+#[test]
+fn wrong_import_numbers() -> Result<()> {
+    let store = Store::default();
+    let module = Module::new(&store, r#"(module (import "" "" (func)))"#)?;
+
+    assert!(Instance::new(&module, &[]).is_err());
+    let func = Func::wrap(&store, || {});
+    assert!(Instance::new(&module, &[func.clone().into(), func.into()]).is_err());
+    Ok(())
+}