From c2a1b07fe378f71a73f379aeeb9b84a35997c21e Mon Sep 17 00:00:00 2001
From: Yingchi Long <i@lyc.dev>
Date: Tue, 19 Sep 2023 22:23:28 +0800
Subject: [PATCH] nixd/Sema: lowering for inherited attrs

---
 nixd/include/nixd/Sema/Lowering.h |   2 +
 nixd/lib/Sema/Lowering.cpp        | 108 ++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)

diff --git a/nixd/include/nixd/Sema/Lowering.h b/nixd/include/nixd/Sema/Lowering.h
index 312c6f976..d69bf507e 100644
--- a/nixd/include/nixd/Sema/Lowering.h
+++ b/nixd/include/nixd/Sema/Lowering.h
@@ -18,6 +18,8 @@ struct Lowering {
   nix::Expr *lower(syntax::Node *Root);
   nix::ExprLambda *lowerFunction(syntax::Function *Fn);
   nix::Formal lowerFormal(const syntax::Formal &Formal);
+  nix::AttrPath lowerAttrPath(const syntax::AttrPath &Path);
+  nix::ExprAttrs *lowerBinds(const syntax::Binds &Binds);
 };
 
 } // namespace nixd
diff --git a/nixd/lib/Sema/Lowering.cpp b/nixd/lib/Sema/Lowering.cpp
index 39c07c9e5..0efa8fb0f 100644
--- a/nixd/lib/Sema/Lowering.cpp
+++ b/nixd/lib/Sema/Lowering.cpp
@@ -3,6 +3,10 @@
 #include "nixd/Syntax/Diagnostic.h"
 #include "nixd/Syntax/Nodes.h"
 
+#include <nix/nixexpr.hh>
+
+#include <llvm/Support/FormatVariadic.h>
+
 namespace nixd {
 
 nix::Formal Lowering::lowerFormal(const syntax::Formal &Formal) {
@@ -109,6 +113,107 @@ nix::ExprLambda *Lowering::lowerFunction(syntax::Function *Fn) {
   return NewLambda;
 }
 
+static syntax::Diagnostic mkDiagDup(std::string Name, RangeIdx Range,
+                                    RangeIdx Prev) {
+  syntax::Diagnostic Diag;
+  Diag.Kind = syntax::Diagnostic::Warning;
+  Diag.Msg = llvm::formatv("duplicated attr {0}", Name);
+  Diag.Range = Range;
+
+  syntax::Note Note;
+  Note.Msg = llvm::formatv("previously defined here");
+  Note.Range = Prev;
+  return Diag;
+}
+
+nix::ExprAttrs *Lowering::lowerBinds(const syntax::Binds &Binds) {
+  // The official parser does this work during the lowering process, via
+  // @addAttr in Parser.y
+
+  using syntax::Node;
+
+  auto *Result = new nix::ExprAttrs;
+  Ctx.Pool.record(Result);
+
+  // Use a map to detect duplicated fields
+  // Not using the map inside nix::ExprAttrs because we want to preserve the
+  // range
+  std::map<nix::Symbol, Node *> Fields;
+
+  for (auto *Attr : Binds.Attributes) {
+    switch (Attr->getKind()) {
+    case Node::NK_Attribute: {
+      auto *Attribute = dynamic_cast<syntax::Attribute *>(Attr);
+      nix::Expr *E = lower(Attribute->Body);
+      break;
+    }
+    case Node::NK_InheritedAttribute: {
+      auto *IA = dynamic_cast<syntax::InheritedAttribute *>(Attr);
+      if (IA->InheritedAttrs->Names.empty()) {
+        syntax::Diagnostic Diag;
+        Diag.Kind = syntax::Diagnostic::Warning;
+        Diag.Msg = "empty inherit expression";
+        Diag.Range = Attr->Range;
+        Diags.emplace_back(std::move(Diag));
+      }
+
+      // inherit (expr) attr1 attr2
+      // lowering `(expr)` to nix expression
+      nix::Expr *Subject = nullptr;
+
+      if (IA->E)
+        Subject = lower(IA->E);
+
+      for (Node *Name : IA->InheritedAttrs->Names) {
+
+        // Extract nix::Symbol, report error if we encountered dynamic fields
+        nix::Symbol Sym;
+        switch (Name->getKind()) {
+        case Node::NK_Identifier: {
+          Sym = dynamic_cast<syntax::Identifier *>(Name)->Symbol;
+          break;
+        }
+        case Node::NK_String: {
+          Sym = STable.create(dynamic_cast<syntax::String *>(Name)->S);
+          break;
+        }
+        default: {
+          syntax::Diagnostic Diag;
+          Diag.Kind = syntax::Diagnostic::Error;
+          Diag.Msg = "dynamic attributes are not allowed in inherit";
+          Diag.Range = Name->Range;
+          Diags.emplace_back(std::move(Diag));
+        }
+        }
+
+        // Check if it is duplicated
+        if (Fields.contains(Sym)) {
+          std::string SymStr = STable[Sym];
+          auto Diag = mkDiagDup(SymStr, Name->Range, Fields[Sym]->Range);
+          Diags.emplace_back(std::move(Diag));
+          continue;
+        }
+
+        // Insert an AttrDef to the result
+        nix::Expr *AttrBody;
+        if (Subject) {
+          // inherit (expr) attr1 attr2
+          AttrBody = new nix::ExprSelect(Name->Range.Begin, Subject, Sym);
+        } else {
+          // inherit attr1 attr2 ...
+          AttrBody = new nix::ExprVar(Name->Range.Begin, Sym);
+        }
+        Ctx.Pool.record(AttrBody);
+        nix::ExprAttrs::AttrDef Def(AttrBody, Name->Range.Begin, true);
+        Result->attrs.insert({Sym, Def});
+      }
+    }
+    }
+  }
+
+  return Result;
+}
+
 nix::Expr *Lowering::lower(nixd::syntax::Node *Root) {
   if (!Root)
     return nullptr;
@@ -136,6 +241,9 @@ nix::Expr *Lowering::lower(nixd::syntax::Node *Root) {
         Ctx.Pool.record(new nix::ExprWith(With->Range.Begin, Attrs, Body));
     return NixWith;
   }
+  case Node::NK_Binds: {
+    auto *Binds = dynamic_cast<syntax::Binds *>(Root);
+  }
   }
 
   return nullptr;