Propagate optional import names to the wasmtime/C API

With the module linking proposal the field name on imports is now
optional, and only the module is required to be specified. This commit
propagates this API change to the boundary of wasmtime's API, ensuring
consumers are aware of what's optional with module linking and what
isn't. Note that it's expected that all existing users will either
update accordingly or unwrap the result since module linking is
presumably disabled.

cranelift/wasm/src/environ/dummy.rs

@@ -581,7 +581,7 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         &mut self,
         index: TypeIndex,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         assert_eq!(
             self.info.functions.len(),
@@ -591,7 +591,7 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         self.info.functions.push(Exportable::new(index));
         self.info
             .imported_funcs
-            .push((String::from(module), String::from(field)));
+            .push((String::from(module), String::from(field.unwrap())));
         Ok(())
     }
 
@@ -609,12 +609,12 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         &mut self,
         global: Global,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         self.info.globals.push(Exportable::new(global));
         self.info
             .imported_globals
-            .push((String::from(module), String::from(field)));
+            .push((String::from(module), String::from(field.unwrap())));
         Ok(())
     }
 
@@ -627,12 +627,12 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         &mut self,
         table: Table,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         self.info.tables.push(Exportable::new(table));
         self.info
             .imported_tables
-            .push((String::from(module), String::from(field)));
+            .push((String::from(module), String::from(field.unwrap())));
         Ok(())
     }
 
@@ -672,12 +672,12 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         &mut self,
         memory: Memory,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         self.info.memories.push(Exportable::new(memory));
         self.info
             .imported_memories
-            .push((String::from(module), String::from(field)));
+            .push((String::from(module), String::from(field.unwrap())));
         Ok(())
     }
 

cranelift/wasm/src/environ/spec.rs

@@ -674,7 +674,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         index: TypeIndex,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()>;
 
     /// Declares a table import to the environment.
@@ -682,7 +682,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         table: Table,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()>;
 
     /// Declares a memory import to the environment.
@@ -690,7 +690,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         memory: Memory,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()>;
 
     /// Declares an event import to the environment.
@@ -698,7 +698,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         event: Event,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         drop((event, module, field));
         Err(WasmError::Unsupported("wasm events".to_string()))
@@ -709,7 +709,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         global: Global,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()>;
 
     /// Declares a module import to the environment.
@@ -717,7 +717,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         ty_index: TypeIndex,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         drop((ty_index, module, field));
         Err(WasmError::Unsupported("module linking".to_string()))
@@ -728,7 +728,7 @@ pub trait ModuleEnvironment<'data>: TargetEnvironment {
         &mut self,
         ty_index: TypeIndex,
         module: &'data str,
-        field: &'data str,
+        field: Option<&'data str>,
     ) -> WasmResult<()> {
         drop((ty_index, module, field));
         Err(WasmError::Unsupported("module linking".to_string()))