[new] Infer extension requirements

src/builder/dataflow.rs

@@ -96,8 +96,9 @@ impl DFGBuilder<Hugr> {
 }
 
 impl HugrBuilder for DFGBuilder<Hugr> {
-    fn finish_hugr(self) -> Result<Hugr, ValidationError> {
-        self.base.validate()?;
+    fn finish_hugr(mut self) -> Result<Hugr, ValidationError> {
+        let closure = self.base.infer_extensions()?;
+        self.base.validate_with_extension_closure(closure)?;
         Ok(self.base)
     }
 }

src/extension.rs

@@ -17,6 +17,9 @@ use crate::types::type_param::{check_type_arg, TypeArgError};
 use crate::types::type_param::{TypeArg, TypeParam};
 use crate::types::CustomType;
 
+mod infer;
+pub use infer::{infer_extensions, ExtensionSolution, InferExtensionError};
+
 mod op_def;
 pub use op_def::{CustomSignatureFunc, OpDef};
 mod type_def;