tamer: asg::graph: Revert removal of AsgRelMut::pre_add_edge commit callback

I changed my mind from the previous commit---I do in fact want to inhibit
edge additions in some cases, to override what is added (e.g. to wrap a
template application in an Expr workspace).

The approach that I was trying to take was to override `from_oi` and return
it to the caller, but with all the dynamic edges, that ended up being a lot
more code than I feel was worth it; it was too complex.  This is a much
simpler (and more flexible) approach---we simply carry out whatever graph
operations we want in `pre_add_edge` using the provided `asg` reference, and
then after we're done, simply omit `commit` on the original.

DEV-13163

tamer/src/asg/graph.rs

@@ -211,8 +211,8 @@ impl Asg {
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
     ) -> Result<(), AsgError> {
-        from_oi.pre_add_edge(self, to_oi, ctx_span).map(|()| {
+        from_oi.pre_add_edge(self, to_oi, ctx_span, |asg| {
-            self.graph.add_edge(
+            asg.graph.add_edge(
                 from_oi.widen().into(),
                 to_oi.into(),
                 (from_oi.src_rel_ty(), OB::rel_ty(), ctx_span),
@@ -512,6 +512,7 @@ pub trait AsgRelMut<OB: ObjectRelatable>: ObjectRelatable {
     fn pre_add_edge(
         asg: &mut Asg,
         rel: ProposedRel<Self, OB>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError>;
 }
 
@@ -528,11 +529,12 @@ impl<OA: ObjectRelatable, OB: ObjectRelatable> AsgRelMut<OB> for OA {
     ///     overridden for a particular edge for a particular object
     ///       (see [`object::tpl`] as an example).
     default fn pre_add_edge(
-        _asg: &mut Asg,
+        asg: &mut Asg,
         _rel: ProposedRel<Self, OB>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         let _ = _rel.ctx_span; // TODO: remove when used (dead_code)
-        Ok(())
+        Ok(commit(asg))
     }
 }
 

tamer/src/asg/graph/object/rel.rs

@@ -864,6 +864,7 @@ pub trait ObjectIndexRelTo<OB: ObjectRelatable>: Sized + Clone + Copy {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError>;
 
     /// Check whether an edge exists from `self` to `to_oi`.
@@ -947,6 +948,7 @@ where
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         O::pre_add_edge(
             asg,
@@ -955,6 +957,7 @@ where
                 to_oi,
                 ctx_span,
             },
+            commit,
         )
     }
 }
@@ -975,6 +978,7 @@ impl<OB: ObjectRelatable> ObjectIndexRelTo<OB> for ObjectIndexTo<OB> {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         macro_rules! pre_add_edge {
             ($ty:ident) => {
@@ -985,6 +989,7 @@ impl<OB: ObjectRelatable> ObjectIndexRelTo<OB> for ObjectIndexTo<OB> {
                         to_oi,
                         ctx_span,
                     },
+                    commit,
                 )
             };
         }
@@ -1019,9 +1024,10 @@ impl<OB: ObjectRelatable> ObjectIndexRelTo<OB> for ObjectIndexToTree<OB> {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
+        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         match self {
-            Self(oito) => oito.pre_add_edge(asg, to_oi, ctx_span),
+            Self(oito) => oito.pre_add_edge(asg, to_oi, ctx_span, commit),
         }
     }
 }

tamer/src/asg/graph/object/tpl.rs

@@ -221,6 +221,7 @@ object_rel! {
             fn pre_add_edge(
                 asg: &mut Asg,
                 rel: ProposedRel<Self, Expr>,
+                commit: impl FnOnce(&mut Asg),
             ) -> Result<(), AsgError> {
                 let tpl_name = rel.from_oi.name(asg);
                 let span = rel.to_oi.resolve(asg).span();
@@ -228,7 +229,9 @@ object_rel! {
                 rel.from_oi.try_map_obj_inner(
                     asg,
                     try_adapt_to(TplShape::Expr(span), tpl_name),
-                ).map(|_| ())
+                )?;
+
+                Ok(commit(asg))
             }
         },
 
@@ -241,6 +244,7 @@ object_rel! {
             fn pre_add_edge(
                 asg: &mut Asg,
                 rel: ProposedRel<Self, Tpl>,
+                commit: impl FnOnce(&mut Asg),
             ) -> Result<(), AsgError> {
                 let tpl_name = rel.from_oi.name(asg);
                 let apply = rel.to_oi.resolve(asg);
@@ -251,7 +255,9 @@ object_rel! {
                 rel.from_oi.try_map_obj_inner(
                     asg,
                     try_adapt_to(apply_shape, tpl_name),
-                ).map(|_| ())
+                )?;
+
+                Ok(commit(asg))
             }
         },