feat(xatu): add lexical scope graph

src/xatu/scope_graph_test.rs

@@ -0,0 +1,76 @@
+use googletest::matchers::eq;
+use googletest::{expect_that, gtest};
+use xatu::{PathStep, Resolution, ResolutionPath, ScopeGraph};
+
+#[gtest]
+fn resolves_a_local_declaration() {
+    let mut graph = ScopeGraph::new();
+    let scope = graph.root_scope();
+    let declaration = graph.add_declaration(scope, "value");
+    let reference = graph.add_reference(scope, "value");
+
+    let expected = vec![resolution(declaration, vec![PathStep::Declaration(declaration)])];
+    expect_that!(graph.resolve(reference), eq(&expected));
+}
+
+#[gtest]
+fn resolves_a_parent_declaration() {
+    let mut graph = ScopeGraph::new();
+    let parent = graph.root_scope();
+    let declaration = graph.add_declaration(parent, "value");
+    let child = graph.add_scope(parent);
+    let reference = graph.add_reference(child, "value");
+
+    let expected = vec![resolution(
+        declaration,
+        vec![PathStep::Parent, PathStep::Declaration(declaration)],
+    )];
+    expect_that!(graph.resolve(reference), eq(&expected));
+}
+
+#[gtest]
+fn local_declarations_shadow_parent_declarations() {
+    let mut graph = ScopeGraph::new();
+    let parent = graph.root_scope();
+    graph.add_declaration(parent, "value");
+    let child = graph.add_scope(parent);
+    let declaration = graph.add_declaration(child, "value");
+    let reference = graph.add_reference(child, "value");
+
+    let expected = vec![resolution(declaration, vec![PathStep::Declaration(declaration)])];
+    expect_that!(graph.resolve(reference), eq(&expected));
+}
+
+#[gtest]
+fn preserves_ambiguous_local_declarations() {
+    let mut graph = ScopeGraph::new();
+    let scope = graph.root_scope();
+    let first = graph.add_declaration(scope, "value");
+    let second = graph.add_declaration(scope, "value");
+    let reference = graph.add_reference(scope, "value");
+
+    let expected = vec![
+        resolution(first, vec![PathStep::Declaration(first)]),
+        resolution(second, vec![PathStep::Declaration(second)]),
+    ];
+    expect_that!(graph.resolve(reference), eq(&expected));
+}
+
+#[gtest]
+fn leaves_unresolved_references_without_resolutions() {
+    let mut graph = ScopeGraph::new();
+    let reference = graph.add_reference(graph.root_scope(), "value");
+
+    let expected = Vec::<Resolution>::new();
+    expect_that!(graph.resolve(reference), eq(&expected));
+}
+
+fn resolution(
+    declaration: xatu::DeclarationId,
+    steps: Vec<PathStep>,
+) -> Resolution {
+    Resolution {
+        declaration,
+        path: ResolutionPath { steps },
+    }
+}