Add dfg_builder_endo that was hinted by the docs removed

hugr-core/src/builder/build_traits.rs

@@ -18,7 +18,9 @@ use crate::{
     types::EdgeKind,
 };
 
-use crate::extension::{ExtensionRegistry, ExtensionSet, SignatureError, PRELUDE_REGISTRY};
+use crate::extension::{
+    ExtensionRegistry, ExtensionSet, SignatureError, PRELUDE_REGISTRY, TO_BE_INFERRED,
+};
 use crate::types::{FunctionType, PolyFuncType, Type, TypeArg, TypeRow};
 
 use itertools::Itertools;
@@ -285,6 +287,21 @@ pub trait Dataflow: Container {
         DFGBuilder::create_with_io(self.hugr_mut(), dfg_n, signature)
     }
 
+    /// Return a builder for a [`crate::ops::DFG`] node, i.e. a nested dataflow subgraph,
+    /// that is endomorphic (the output types are the same as the input types).
+    /// The `inputs` must be an iterable over pairs of the type of the input and
+    /// the corresponding wire.
+    fn dfg_builder_endo(
+        &mut self,
+        inputs: impl IntoIterator<Item = (Type, Wire)>,
+    ) -> Result<DFGBuilder<&mut Hugr>, BuildError> {
+        let (types, input_wires): (Vec<Type>, Vec<Wire>) = inputs.into_iter().unzip();
+        self.dfg_builder(
+            FunctionType::new_endo(types).with_extension_delta(TO_BE_INFERRED),
+            input_wires,
+        )
+    }
+
     /// Return a builder for a [`crate::ops::CFG`] node,
     /// i.e. a nested controlflow subgraph.
     /// The `inputs` must be an iterable over pairs of the type of the input and

hugr-core/src/hugr/rewrite/inline_dfg.rs

@@ -195,7 +195,7 @@ mod test {
         }
         let c1 = nonlocal.then(|| make_const(&mut outer));
         let inner = {
-            let mut inner = outer.dfg_builder(ft1(int_ty.clone()), [a])?;
+            let mut inner = outer.dfg_builder_endo([(int_ty.clone(), a)])?;
             let [a] = inner.input_wires_arr();
             let c1 = c1.unwrap_or_else(|| make_const(&mut inner))?;
             let a1 = inner.add_dataflow_op(IntOpDef::iadd.with_log_width(6), [a, c1])?;