From 24d3db8687397f9a6d135386b73a3f2c1f3c9f8e Mon Sep 17 00:00:00 2001
From: Guanghui Hu <120L052208@stu.hit.edu.cn>
Date: Thu, 21 Sep 2023 22:07:45 +0800
Subject: [PATCH] nixd/Sema: lowering some operators (binary + unary)

Co-authored-by: Yingchi Long <i@lyc.dev>
---
 nixd/include/nixd/Sema/EvalContext.h       |   2 +
 nixd/include/nixd/Sema/Lowering.h          |  59 ++++++++++++
 nixd/lib/Sema/Lowering.cpp                 | 106 +++++++++++++++++++++
 nixd/tools/nixd-lint/test/lowering-ops.nix |  58 +++++++++++
 4 files changed, 225 insertions(+)
 create mode 100644 nixd/tools/nixd-lint/test/lowering-ops.nix

diff --git a/nixd/include/nixd/Sema/EvalContext.h b/nixd/include/nixd/Sema/EvalContext.h
index 146a26320..12260a6e5 100644
--- a/nixd/include/nixd/Sema/EvalContext.h
+++ b/nixd/include/nixd/Sema/EvalContext.h
@@ -7,8 +7,10 @@
 namespace nixd {
 
 struct EvalContext {
+  using ES = std::vector<std::pair<nix::PosIdx, nix::Expr *>>;
   GCPool<nix::Expr> Pool;
   GCPool<nix::Formals> FormalsPool;
+  GCPool<ES> ESPool;
 };
 
 } // namespace nixd
diff --git a/nixd/include/nixd/Sema/Lowering.h b/nixd/include/nixd/Sema/Lowering.h
index f6d20ff7a..d792be59f 100644
--- a/nixd/include/nixd/Sema/Lowering.h
+++ b/nixd/include/nixd/Sema/Lowering.h
@@ -60,6 +60,65 @@ struct Lowering {
   nix::ExprLambda *lowerFunction(const syntax::Function *Fn);
   nix::Formal lowerFormal(const syntax::Formal &Formal);
   nix::AttrPath lowerAttrPath(const syntax::AttrPath &Path);
+  nix::Expr *lowerOp(const syntax::Node *Op);
+
+private:
+  constexpr static std::string_view LessThan = "__lessThan";
+  constexpr static std::string_view Sub = "__sub";
+  constexpr static std::string_view Mul = "__mul";
+  constexpr static std::string_view Div = "__div";
+
+  nix::ExprVar *mkVar(std::string_view Sym) {
+    return mkVar(STable.create(Sym));
+  }
+
+  nix::ExprVar *mkVar(nix::Symbol Sym) {
+    auto *Var = new nix::ExprVar(Sym);
+    Ctx.Pool.record(Var);
+    return Var;
+  };
+
+  nix::ExprOpNot *mkNot(nix::Expr *Body) {
+    auto *OpNot = new nix::ExprOpNot(Body);
+    Ctx.Pool.record(OpNot);
+    return OpNot;
+  }
+
+  nix::ExprCall *mkCall(std::string_view FnName, nix::PosIdx P,
+                        std::vector<nix::Expr *> Args) {
+    nix::ExprVar *Fn = mkVar(FnName);
+    auto *Nix = new nix::ExprCall(P, Fn, std::move(Args));
+    return Ctx.Pool.record(Nix);
+  }
+
+  template <class SyntaxTy>
+  nix::Expr *lowerCallOp(std::string_view FnName, const syntax::Node *Op,
+                         bool SwapOperands = false, bool Not = false) {
+    auto *SOP = dynamic_cast<const SyntaxTy *>(Op);
+    assert(SOP && "types are not matching between op pointer & syntax type!");
+    nix::Expr *LHS = lower(SOP->LHS);
+    nix::Expr *RHS = lower(SOP->RHS);
+    if (SwapOperands)
+      std::swap(LHS, RHS);
+    nix::PosIdx P = SOP->OpRange.Begin;
+    nix::ExprCall *Call = mkCall(FnName, P, {LHS, RHS});
+    if (Not)
+      return mkNot(Call);
+    return Call;
+  }
+
+  /// The bin-op expression is actually legal in the nix evaluator
+  /// OpImpl -> nix::ExprOpImpl
+  template <class NixTy, class SyntaxTy>
+  NixTy *lowerLegalOp(const syntax::Node *Op) {
+    auto *SOP = dynamic_cast<const SyntaxTy *>(Op);
+    assert(SOP && "types are not matching between op pointer & syntax type!");
+    nix::Expr *LHS = lower(SOP->LHS);
+    nix::Expr *RHS = lower(SOP->RHS);
+    nix::PosIdx P = SOP->OpRange.Begin;
+    auto *Nix = new NixTy(P, LHS, RHS);
+    return Ctx.Pool.record(Nix);
+  }
 };
 
 } // namespace nixd
diff --git a/nixd/lib/Sema/Lowering.cpp b/nixd/lib/Sema/Lowering.cpp
index 9bf6724a5..97fa2ab86 100644
--- a/nixd/lib/Sema/Lowering.cpp
+++ b/nixd/lib/Sema/Lowering.cpp
@@ -6,6 +6,7 @@
 
 #include <nix/nixexpr.hh>
 
+#include <llvm/Support/ErrorHandling.h>
 #include <llvm/Support/FormatVariadic.h>
 
 #include <memory>
@@ -381,6 +382,101 @@ void ExprAttrsBuilder::addInherited(const syntax::InheritedAttribute &IA) {
   }
 }
 
+nix::Expr *Lowering::lowerOp(const syntax::Node *Op) {
+  if (!Op)
+    return nullptr;
+
+  switch (Op->getKind()) {
+  case Node::NK_OpNot: {
+    const auto *OpNot = dynamic_cast<const syntax::OpNot *>(Op);
+    return mkNot(lower(OpNot->Body));
+  }
+
+  // arithmetic
+  case Node::NK_OpAdd: {
+    // A + B
+    // ->
+    // ExprConcatStrings:
+    //   - pos: "+"
+    //   - forceString: false
+    //   - es: {{A.pos, A}, {B.pos, B}}
+    const auto *OpAdd = dynamic_cast<const syntax::OpAdd *>(Op);
+    nix::Expr *A = lower(OpAdd->LHS);
+    nix::Expr *B = lower(OpAdd->RHS);
+    nix::PosIdx APos = OpAdd->LHS->Range.Begin;
+    nix::PosIdx BPos = OpAdd->RHS->Range.Begin;
+    nix::PosIdx Pos = OpAdd->OpRange.Begin;
+    auto *ES = Ctx.ESPool.record(new EvalContext::ES{{APos, A}, {BPos, B}});
+    auto ECS = new nix::ExprConcatStrings(Pos, /*forceString=*/false, ES);
+    return Ctx.Pool.record(ECS);
+  }
+  case Node::NK_OpSub:
+    return lowerCallOp<syntax::OpSub>(Sub, Op);
+  case Node::NK_OpMul:
+    return lowerCallOp<syntax::OpMul>(Mul, Op);
+  case Node::NK_OpDiv:
+    return lowerCallOp<syntax::OpDiv>(Div, Op);
+
+  // comparison
+  case Node::NK_OpNegate: {
+    // -X
+    // ->
+    // (__sub 0 X)
+    const auto *OpNegate = dynamic_cast<const syntax::OpNegate *>(Op);
+    nix::Expr *I0 = Ctx.Pool.record(new nix::ExprInt(0));
+    nix::Expr *X = lower(OpNegate->Body);
+    nix::PosIdx P = OpNegate->OpRange.Begin;
+    return mkCall(Sub, P, {I0, X});
+  }
+  case Node::NK_OpLe: {
+    // A < B
+    // ->
+    // (__lessThan A B)
+    return lowerCallOp<syntax::OpLe>(LessThan, Op);
+  }
+  case Node::NK_OpLeq: {
+    // A <= B
+    // ->
+    // (! (__lessThan B A))
+    return lowerCallOp<syntax::OpLeq>(LessThan, Op, /*SwapOperands=*/true,
+                                      /*Not=*/true);
+  }
+  case Node::NK_OpGe: {
+    // A > B
+    // ->
+    // (__lessThan B A)
+    return lowerCallOp<syntax::OpGe>(LessThan, Op, /*SwapOperands=*/true);
+  }
+  case Node::NK_OpGeq: {
+    // A >= B
+    // ->
+    // ! (__lessThan A B)
+    return lowerCallOp<syntax::OpGeq>(LessThan, Op, /*SwapOperands=*/false,
+                                      /*Not=*/true);
+  }
+
+  // legal nodes, the list here has the same order with official parser.
+  // src/libexpr/nixexpr.hh, `MakeBinOp`
+  case Node::NK_OpEq:
+    return lowerLegalOp<nix::ExprOpEq, syntax::OpEq>(Op);
+  case Node::NK_OpNEq:
+    return lowerLegalOp<nix::ExprOpNEq, syntax::OpNEq>(Op);
+  case Node::NK_OpAnd:
+    return lowerLegalOp<nix::ExprOpAnd, syntax::OpAnd>(Op);
+  case Node::NK_OpOr:
+    return lowerLegalOp<nix::ExprOpOr, syntax::OpOr>(Op);
+  case Node::NK_OpImpl:
+    return lowerLegalOp<nix::ExprOpImpl, syntax::OpImpl>(Op);
+  case Node::NK_OpUpdate:
+    return lowerLegalOp<nix::ExprOpUpdate, syntax::OpUpdate>(Op);
+  case Node::NK_OpConcatLists:
+    return lowerLegalOp<nix::ExprOpConcatLists, syntax::OpConcatLists>(Op);
+  default:
+    llvm_unreachable("do not know how to lower this op!");
+  }
+  return nullptr;
+}
+
 nix::Expr *Lowering::lower(const syntax::Node *Root) {
   if (!Root)
     return nullptr;
@@ -445,6 +541,16 @@ nix::Expr *Lowering::lower(const syntax::Node *Root) {
         Ctx.Pool.record(new nix::ExprIf(If->Range.Begin, Cond, Then, Else));
     return NixIf;
   }
+
+  // operators
+  case Node::NK_OpNot:
+  case Node::NK_OpNegate:
+#define BIN_OP(NAME, _) case Node::NK_##NAME:
+#include "nixd/Syntax/BinaryOps.inc"
+#undef BIN_OP
+  {
+    return lowerOp(Root);
+  }
   }
 
   return nullptr;
diff --git a/nixd/tools/nixd-lint/test/lowering-ops.nix b/nixd/tools/nixd-lint/test/lowering-ops.nix
new file mode 100644
index 000000000..34f1f2935
--- /dev/null
+++ b/nixd/tools/nixd-lint/test/lowering-ops.nix
@@ -0,0 +1,58 @@
+# RUN: nixd-lint -dump-nix-ast %s | FileCheck %s
+# RUN: nixd-lint -dump-nix-ast -show-position %s | FileCheck --check-prefix=POSITION %s
+
+{
+  # POSITION: ExprCall: (__sub 0 1) 6:14
+  Position = -1;
+
+  # CHECK: ExprOpNot: (! 1)
+  Not = !1;
+
+  # CHECK: ExprCall: (__sub 0 1)
+  Negate = -1;
+
+  # CHECK: ExprOpEq: (1 == 1)
+  Eq = 1 == 1;
+
+  # CHECK: ExprOpNEq: (1 != 1)
+  NEq = 1 != 1;
+
+  # CHECK: ExprCall: (__lessThan 2 1)
+  Ge = 1 > 2;
+
+  # CHECK: ExprCall: (__lessThan 1 2)
+  Le = 1 < 2;
+
+  # CHECK: (! (__lessThan 2 1))
+  Leq = 1 <= 2;
+
+  # CHECK: ExprOpNot: (! (__lessThan 1 2))
+  Geq = 1 >= 2;
+
+  # CHECK:  ExprOpAnd: (1 && 2)
+  And = 1 && 2;
+
+  # CHECK: ExprOpOr: (1 || 2)
+  Or = 1 || 2;
+
+  # CHECK: ExprOpImpl: (1 -> 2)
+  Impl = 1 -> 2;
+
+  # CHECK: ExprOpUpdate: (1 // 2)
+  Update = 1 // 2;
+
+  # CHECK: ExprConcatStrings: (1 + 2)
+  Add = 1 + 2;
+
+  # CHECK: ExprCall: (__sub 1 2)
+  Sub = 1 - 2;
+
+  # CHECK: ExprCall: (__mul 1 2)
+  Mul = 1 * 2;
+
+  # CHECK: ExprCall: (__div 1 2)
+  Div = 1 / 2;
+
+  # CHECK: ExprOpConcatLists: (1 ++ 2)
+  Concat = 1 ++ 2;
+}