Add method to eliminate precondition stack variables

Author: Hendrik van Antwerpen

stack-graphs/src/partial.rs

@@ -2302,6 +2302,45 @@ impl PartialPath {
             .with_offset(scope_variable_offset);
     }
 
+    /// Replaces stack variables in the precondition with empty stacks.
+    pub fn eliminate_precondition_stack_variables(&mut self, partials: &mut PartialPaths) {
+        let mut symbol_bindings = PartialSymbolStackBindings::new();
+        let mut scope_bindings = PartialScopeStackBindings::new();
+        if let Some(symbol_variable) = self.symbol_stack_precondition.variable() {
+            symbol_bindings
+                .add(
+                    partials,
+                    symbol_variable,
+                    PartialSymbolStack::empty(),
+                    &mut scope_bindings,
+                )
+                .unwrap();
+        }
+        if let Some(scope_variable) = self.scope_stack_precondition.variable() {
+            scope_bindings
+                .add(partials, scope_variable, PartialScopeStack::empty())
+                .unwrap();
+        }
+
+        self.symbol_stack_precondition = self
+            .symbol_stack_precondition
+            .apply_partial_bindings(partials, &symbol_bindings, &scope_bindings)
+            .unwrap();
+        self.scope_stack_precondition = self
+            .scope_stack_precondition
+            .apply_partial_bindings(partials, &scope_bindings)
+            .unwrap();
+
+        self.symbol_stack_postcondition = self
+            .symbol_stack_postcondition
+            .apply_partial_bindings(partials, &symbol_bindings, &scope_bindings)
+            .unwrap();
+        self.scope_stack_postcondition = self
+            .scope_stack_postcondition
+            .apply_partial_bindings(partials, &scope_bindings)
+            .unwrap();
+    }
+
     /// Attempts to append an edge to the end of a partial path.  If the edge is not a valid
     /// extension of this partial path, we return an error describing why.
     pub fn append(

stack-graphs/tests/it/partial.rs

@@ -675,5 +675,23 @@ fn can_append_partial_paths() -> Result<(), PathResolutionError> {
         "<%1> ($1) [test(7) push scoped baz test(6)] -> [jump to scope] <baz/([test(6)],$1),%1> ($1)",
     );
 
+    // verify that without stack variables in the precondition, the precondition cannot grow because of concatenation
+    {
+        let left = &[scope0];
+        let right = &[scope0, bar_def];
+
+        let mut g = StackGraph::new();
+        g.add_from_graph(&graph).expect("");
+
+        let mut ps = PartialPaths::new();
+        let mut l = create_partial_path_and_edges(&mut g, &mut ps, left).expect("");
+        l.eliminate_precondition_stack_variables(&mut ps);
+        let mut r = create_partial_path_and_edges(&mut g, &mut ps, right).expect("");
+
+        r.ensure_no_overlapping_variables(&mut ps, &l);
+        let result = l.concatenate(&g, &mut ps, &r);
+        result.expect_err("");
+    }
+
     Ok(())
 }