Fix direct imports in --target web

Currently the import object constructed for the `--target web` output
only ever includes the current module as an one of the modules included.
With `wasm-bindgen`'s optimization to import directly from modules,
however, it's possible to have more modules imported from in the
generated wasm file. This commit ensures that the imports are hooked up
in the `--target web` es6 emulation mode, ensuring there aren't
extraneous errors about import objects.

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

@@ -13,7 +13,7 @@ use crate::{
 };
 use failure::{bail, Error, ResultExt};
 use std::{
-    collections::{BTreeMap, HashMap, HashSet},
+    collections::{BTreeMap, HashMap, HashSet, BTreeSet},
     env, fs,
 };
 use walrus::{MemoryId, Module};
@@ -918,13 +918,41 @@ impl<'a> Context<'a> {
         } else {
             ""
         };
-
         let ts = Self::ts_for_init_fn(mem.import.is_some());
+
+        // Generate extra initialization for the `imports` object if necessary
+        // based on the values in `direct_imports` we find. These functions are
+        // intended to be imported directly to the wasm module and we need to
+        // ensure that the modules are actually imported from and inserted into
+        // the object correctly.
+        let mut map = BTreeMap::new();
+        for &(module, name) in self.direct_imports.values() {
+            map.entry(module).or_insert(BTreeSet::new()).insert(name);
+        }
+        let mut imports_init = String::new();
+        for (module, names) in map {
+            imports_init.push_str("imports['");
+            imports_init.push_str(module);
+            imports_init.push_str("'] = { ");
+            for (i, name) in names.into_iter().enumerate() {
+                if i != 0 {
+                    imports_init.push_str(", ");
+                }
+                let import = Import::Module { module, name, field: None };
+                let identifier = self.import_identifier(import);
+                imports_init.push_str(name);
+                imports_init.push_str(": ");
+                imports_init.push_str(&identifier);
+            }
+            imports_init.push_str(" };\n");
+        }
+
         let js = format!(
             "\
                 function init(module{init_memory_arg}) {{
                     let result;
                     const imports = {{ './{module}': __exports }};
+                    {imports_init}
                     if (module instanceof URL || typeof module === 'string' || module instanceof Request) {{
                         {init_memory2}
                         const response = fetch(module);
@@ -973,6 +1001,7 @@ impl<'a> Context<'a> {
             } else {
                 ""
             },
+            imports_init = imports_init,
         );
 
         (js, ts)

tests/headless/main.rs

@@ -39,3 +39,4 @@ fn can_log_html_strings() {
 }
 
 pub mod snippets;
+pub mod modules;

tests/headless/modules.js

@@ -0,0 +1,3 @@
+export function get_five() {
+  return 5;
+}

tests/headless/modules.rs

@@ -0,0 +1,12 @@
+use wasm_bindgen::prelude::*;
+use wasm_bindgen_test::*;
+
+#[wasm_bindgen(raw_module = "./tests/headless/modules.js")]
+extern "C" {
+    fn get_five() -> u32;
+}
+
+#[wasm_bindgen_test]
+fn test_get_five() {
+    assert_eq!(get_five(), 5);
+}