libnixf: parse pipe operator

Implements: NixOS/rfcs#148
Closes: #554

Author: inclyc

libnixf/include/nixf/Basic/TokenKinds.inc

@@ -93,4 +93,8 @@ TOK_BIN_OP(mul)    // *
 TOK_BIN_OP(div)    // /
 TOK_BIN_OP(concat) // ++
 
+// [RFC 0418 Pipe operator](https://github.com/NixOS/rfcs/pull/148)
+TOK_BIN_OP(pipe_into) // |>
+TOK_BIN_OP(pipe_from) // <|
+
 #endif // TOK_BIN_OP

libnixf/src/Parse/Lexer.cpp

@@ -526,6 +526,8 @@ Token Lexer::lex() {
   case '|':
     if (consumePrefix("||"))
       Tok = tok_op_or;
+    if (consumePrefix("|>"))
+      Tok = tok_op_pipe_into;
     break;
   case '!':
     if (consumePrefix("!=")) {
@@ -538,6 +540,8 @@ Token Lexer::lex() {
   case '<':
     if (consumePrefix("<=")) {
       Tok = tok_op_le;
+    } else if (consumePrefix("<|")) {
+      Tok = tok_op_pipe_from;
     } else {
       consume();
       Tok = tok_op_lt;

libnixf/src/Parse/ParseOp.cpp

@@ -16,6 +16,7 @@ namespace {
 
 /// Binary operators:
 ///
+/// %left |> | %right <|
 /// %right ->
 /// %left ||
 /// %left &&
@@ -30,31 +31,35 @@ namespace {
 /// %nonassoc NEGATE
 std::pair<unsigned, unsigned> getBP(TokenKind Kind) {
   switch (Kind) {
+  case tok_op_pipe_from:
+    return {0, 1};
+  case tok_op_pipe_into:
+    return {1, 0};
   case tok_op_impl: // %right ->
-    return {2, 1};
+    return {3, 2};
   case tok_op_or: // %left ||
-    return {3, 4};
+    return {4, 5};
   case tok_op_and: // %left &&
-    return {5, 6};
+    return {6, 7};
   case tok_op_eq: // %nonassoc == !=
   case tok_op_neq:
-    return {7, 7};
+    return {8, 8};
   case tok_op_lt: // %nonassoc < > <= >=
   case tok_op_le:
   case tok_op_ge:
   case tok_op_gt:
-    return {8, 8};
+    return {9, 9};
   case tok_op_update: // %right //
-    return {10, 9};
-    // %left NOT - 11
+    return {11, 10};
+    // %left NOT - 12
   case tok_op_add: // %left + -
   case tok_op_negate:
-    return {12, 13};
+    return {13, 14};
   case tok_op_mul: // %left * /
-    return {14, 15};
+    return {15, 16};
   case tok_op_div:
   case tok_op_concat: // %right ++
-    return {17, 16};
+    return {18, 17};
   // % op_negate
   default:
     __builtin_unreachable();

libnixf/test/Parse/ParseOp.cpp

@@ -71,4 +71,63 @@ TEST(Parser, OpHasAttr_empty) {
   ASSERT_EQ(Diags.size(), 0);
 }
 
+TEST(Parser, Op_PipeOperator_Forward) {
+  auto Src = R"(a |> b)"sv;
+
+  std::vector<Diagnostic> Diags;
+  Parser P(Src, Diags);
+  auto AST = P.parseExpr();
+
+  ASSERT_TRUE(AST);
+
+  ASSERT_EQ(AST->kind(), Node::NK_ExprBinOp);
+  ASSERT_EQ(Diags.size(), 0);
+}
+
+TEST(Parser, Op_PipeOperator_Forward_LeftAssosiative) {
+  auto Src = R"(a |> b |> c)"sv;
+
+  std::vector<Diagnostic> Diags;
+  Parser P(Src, Diags);
+  auto AST = P.parseExpr();
+
+  ASSERT_TRUE(AST);
+
+  ASSERT_EQ(AST->kind(), Node::NK_ExprBinOp);
+
+  const auto &BinOp = static_cast<const ExprBinOp &>(*AST);
+  ASSERT_EQ(BinOp.lhs()->kind(), Node::NK_ExprVar);
+  ASSERT_EQ(Diags.size(), 0);
+}
+
+TEST(Parser, Op_PipeOperator_Backward) {
+  auto Src = R"(a <| b)"sv;
+
+  std::vector<Diagnostic> Diags;
+  Parser P(Src, Diags);
+  auto AST = P.parseExpr();
+
+  ASSERT_TRUE(AST);
+
+  ASSERT_EQ(AST->kind(), Node::NK_ExprBinOp);
+  ASSERT_EQ(Diags.size(), 0);
+}
+
+TEST(Parser, Op_PipeOperator_Forward_RightAssosiative) {
+  auto Src = R"(a <| b <| c)"sv;
+
+  std::vector<Diagnostic> Diags;
+  Parser P(Src, Diags);
+  auto AST = P.parseExpr();
+
+  ASSERT_TRUE(AST);
+
+  ASSERT_EQ(AST->kind(), Node::NK_ExprBinOp);
+
+  const auto &BinOp = static_cast<const ExprBinOp &>(*AST);
+  ASSERT_EQ(BinOp.lhs()->kind(), Node::NK_ExprBinOp);
+  ASSERT_EQ(BinOp.rhs()->kind(), Node::NK_ExprVar);
+  ASSERT_EQ(Diags.size(), 0);
+}
+
 } // namespace