libnixf: add parent map (#391)

libnixf/include/nixf/Sema/ParentMap.h

@@ -0,0 +1,35 @@
+/// \file
+/// \brief ParentMap analysis.
+///
+/// This is used to construct upward edges. For each node, record it's direct
+/// parent. (Abstract Syntax TREE only have one parent for each node).
+
+#pragma once
+
+#include "nixf/Basic/Nodes/Basic.h"
+
+#include <map>
+
+namespace nixf {
+
+class ParentMapAnalysis {
+  std::map<const Node *, const Node *> ParentMap;
+
+  void dfs(const Node *N, const Node *Parent);
+
+public:
+  void runOnAST(const Node &Root);
+
+  const Node *query(const Node &N);
+
+  static bool isRoot(const Node *Up, const Node &N);
+
+  /// \brief Search up until the node becomes a concrete expression.
+  /// a
+  /// ^<-----   ID -> ExprVar
+  const Node *upExpr(const Node &N);
+
+  bool isRoot(const Node &N);
+};
+
+} // namespace nixf

libnixf/meson.build

@@ -15,6 +15,7 @@ libnixf = library(
     'src/Parse/ParseSimple.cpp',
     'src/Parse/ParseStrings.cpp',
     'src/Parse/ParseSupport.cpp',
+    'src/Sema/ParentMap.cpp',
     'src/Sema/SemaActions.cpp',
     'src/Sema/VariableLookup.cpp',
     include_directories: libnixf_inc,
@@ -68,6 +69,7 @@ test('unit/libnixf/Sema',
     executable('unit-libnixf-sema',
         'test/Sema/SemaActions.cpp',
         'test/Sema/VariableLookup.cpp',
+        'test/Sema/ParentMap.cpp',
         dependencies: [ nixf, gtest_main ],
         include_directories: [ 'src/Sema' ] # Private headers
     )

libnixf/src/Sema/ParentMap.cpp

@@ -0,0 +1,38 @@
+#include "nixf/Sema/ParentMap.h"
+
+using namespace nixf;
+
+void ParentMapAnalysis::dfs(const Node *N, const Node *Parent) {
+  if (!N)
+    return;
+  ParentMap.insert({N, Parent});
+  for (const Node *Ch : N->children())
+    dfs(Ch, N);
+}
+
+const Node *ParentMapAnalysis::query(const Node &N) {
+  return ParentMap.contains(&N) ? ParentMap.at(&N) : nullptr;
+}
+
+const Node *ParentMapAnalysis::upExpr(const Node &N) {
+
+  if (Expr::isExpr(N.kind()))
+    return &N;
+  const Node *Up = query(N);
+  if (isRoot(Up, N) || !Up)
+    return nullptr;
+  return upExpr(*Up);
+}
+
+void ParentMapAnalysis::runOnAST(const Node &Root) {
+  // Special case. Root node has itself as "parent".
+  dfs(&Root, &Root);
+}
+
+bool nixf::ParentMapAnalysis::isRoot(const Node *Up, const Node &N) {
+  return Up == &N;
+}
+
+bool nixf::ParentMapAnalysis::isRoot(const Node &N) {
+  return isRoot(query(N), N);
+}

libnixf/test/Sema/ParentMap.cpp

@@ -0,0 +1,29 @@
+#include <gtest/gtest.h>
+
+#include "nixf/Basic/Diagnostic.h"
+#include "nixf/Parse/Parser.h"
+#include "nixf/Sema/ParentMap.h"
+
+using namespace nixf;
+
+namespace {
+
+struct ParentMapTest : testing::Test {
+  std::vector<Diagnostic> Diags;
+
+  ParentMapAnalysis PMA;
+};
+
+TEST_F(ParentMapTest, Basic) {
+  auto AST = nixf::parse(R"(a)", Diags);
+  PMA.runOnAST(*AST);
+
+  const Node *ID = AST->descend({{0, 0}, {0, 1}});
+  ASSERT_EQ(ID->kind(), Node::NK_Identifer);
+
+  const Node *Var = PMA.upExpr(*ID);
+
+  ASSERT_EQ(Var->kind(), Node::NK_ExprVar);
+}
+
+} // namespace