fix(wasmtime): Fix borrowchecker errors in Wasmtime list lowering (#188)

theduke · web-flow · commit e165c0226ad0 · 2022-04-04T15:19:20.000-05:00
Fixes code generation for Wasmtime list lowering. List lowering happens in a for loop and thus opens a new scope, which invalidates previous caller_memory bindings. This previously was not ensured, resulting in borrow checker errors in the generated code if the items in a list required allocation. The `lists.wit` tests is modified to contain previously problematic definitions. Fixes #187
diff --git a/crates/gen-wasmtime/src/lib.rs b/crates/gen-wasmtime/src/lib.rs
@@ -1998,7 +1998,10 @@ impl Bindgen for FunctionBindgen<'_> {
                 }
             }
 
-            Instruction::IterElem { .. } => results.push("e".to_string()),
+            Instruction::IterElem { .. } => {
+                self.caller_memory_available = false; // invalidated by for loop
+                results.push("e".to_string())
+            }
 
             Instruction::IterBasePointer => results.push("base".to_string()),
 
diff --git a/tests/codegen/lists.wit b/tests/codegen/lists.wit
@@ -29,6 +29,7 @@ string-list: function(x: list<string>) -> list<string>
 record some-record {
   x: string,
   y: other-record,
+  z: list<other-record>,
   c1: u32,
   c2: u64,
   c3: s32,
@@ -43,6 +44,7 @@ record other-record {
   c: list<u8>,
 }
 record-list: function(x: list<some-record>) -> list<other-record>
+record-list-reverse: function(x: list<other-record>) -> list<some-record>
 
 variant some-variant {
   a(string),

Original file line number	Diff line number	Diff line change
`@@ -1998,7 +1998,10 @@ impl Bindgen for FunctionBindgen<'_> {`
`1998`	`1998`	`}`
`1999`	`1999`	`}`
`2000`	`2000`
`2001`		`- Instruction::IterElem { .. } => results.push("e".to_string()),`
	`2001`	`+ Instruction::IterElem { .. } => {`
	`2002`	`+ self.caller_memory_available = false; // invalidated by for loop`
	`2003`	`+ results.push("e".to_string())`
	`2004`	`+ }`
`2002`	`2005`
`2003`	`2006`	`Instruction::IterBasePointer => results.push("base".to_string()),`
`2004`	`2007`