From 36e841d1d60eea10745f0d4db11f5d41646c4844 Mon Sep 17 00:00:00 2001
From: Yingchi Long <i@lyc.dev>
Date: Wed, 18 Sep 2024 11:30:48 +0800
Subject: [PATCH] libnixf: parse pipe operator

Implements: https://github.com/NixOS/rfcs/pull/148
Closes: https://github.com/nix-community/nixd/issues/554
---
 libnixf/include/nixf/Basic/TokenKinds.inc |  4 ++
 libnixf/src/Parse/Lexer.cpp               |  4 ++
 libnixf/src/Parse/ParseOp.cpp             | 25 +++++---
 libnixf/test/Parse/ParseOp.cpp            | 74 +++++++++++++++++++++++
 4 files changed, 97 insertions(+), 10 deletions(-)

diff --git a/libnixf/include/nixf/Basic/TokenKinds.inc b/libnixf/include/nixf/Basic/TokenKinds.inc
index 035cc2c64..b04fc57d6 100644
--- a/libnixf/include/nixf/Basic/TokenKinds.inc
+++ b/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
diff --git a/libnixf/src/Parse/Lexer.cpp b/libnixf/src/Parse/Lexer.cpp
index 9042c440b..971377bbd 100644
--- a/libnixf/src/Parse/Lexer.cpp
+++ b/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;
diff --git a/libnixf/src/Parse/ParseOp.cpp b/libnixf/src/Parse/ParseOp.cpp
index 0e842bb32..772a6cf7e 100644
--- a/libnixf/src/Parse/ParseOp.cpp
+++ b/libnixf/src/Parse/ParseOp.cpp
@@ -17,6 +17,7 @@ namespace {
 
 /// Binary operators:
 ///
+/// %left |> | %right <|
 /// %right ->
 /// %left ||
 /// %left &&
@@ -31,31 +32,35 @@ namespace {
 /// %nonassoc NEGATE
 std::pair<unsigned, unsigned> getBP(TokenKind Kind) {
   switch (Kind) {
-  case tok_op_impl: // %right ->
+  case tok_op_pipe_from:
+    return {1, 2};
+  case tok_op_pipe_into:
     return {2, 1};
+  case tok_op_impl: // %right ->
+    return {4, 3};
   case tok_op_or: // %left ||
-    return {3, 4};
-  case tok_op_and: // %left &&
     return {5, 6};
+  case tok_op_and: // %left &&
+    return {7, 8};
   case tok_op_eq: // %nonassoc == !=
   case tok_op_neq:
-    return {7, 7};
+    return {9, 9};
   case tok_op_lt: // %nonassoc < > <= >=
   case tok_op_le:
   case tok_op_ge:
   case tok_op_gt:
-    return {8, 8};
+    return {10, 10};
   case tok_op_update: // %right //
-    return {10, 9};
-    // %left NOT - 11
+    return {12, 11};
+    // %left NOT - 13
   case tok_op_add: // %left + -
   case tok_op_negate:
-    return {12, 13};
-  case tok_op_mul: // %left * /
     return {14, 15};
+  case tok_op_mul: // %left * /
+    return {16, 17};
   case tok_op_div:
   case tok_op_concat: // %right ++
-    return {17, 16};
+    return {19, 18};
   // % op_negate
   default:
     __builtin_unreachable();
diff --git a/libnixf/test/Parse/ParseOp.cpp b/libnixf/test/Parse/ParseOp.cpp
index 444b37643..fec2826de 100644
--- a/libnixf/test/Parse/ParseOp.cpp
+++ b/libnixf/test/Parse/ParseOp.cpp
@@ -84,4 +84,78 @@ TEST(Parser, Op_NonAssociative) {
   ASSERT_EQ(Diags[0].kind(), Diagnostic::DK_OperatorNotAssociative);
 }
 
+TEST(Parser, Op_PipeOperator_Forward) {
+  auto Src = R"(a |> b)"sv;
+
+  std::vector<Diagnostic> Diags;
+  Parser P(Src, Diags);
+  auto AST = P.parseExpr();
+
+
+  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);
+}
+
+TEST(Parser, Op_PipeOperator_NonAssociative) {
+  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);
+
+  ASSERT_EQ(Diags.size(), 1);
+  ASSERT_EQ(Diags[0].kind(), nixf::Diagnostic::DK_OperatorNotAssociative);
+}
+
 } // namespace