nixd: lib + pkgs completion with "select", e.g. lib.gen|, pkgs.stdenv.mkDerivat|

nixd/include/nixd/Protocol/AttrSet.h

@@ -26,7 +26,13 @@ constexpr inline std::string_view Exit = "exit";
 using EvalExprParams = std::string;
 using EvalExprResponse = std::optional<std::string>;
 
-using AttrPathInfoParams = std::vector<std::string>;
+/// \brief A list of strings that "select"s into a attribute set.
+using Selector = std::vector<std::string>;
+
+using PackageInfoParams = Selector;
+using OptionInfoParams = Selector;
+
+using AttrPathInfoParams = Selector;
 
 struct PackageDescription {
   std::optional<std::string> Name;
@@ -45,7 +51,7 @@ bool fromJSON(const llvm::json::Value &Params, PackageDescription &R,
               llvm::json::Path P);
 
 struct AttrPathCompleteParams {
-  std::vector<std::string> Scope;
+  Selector Scope;
   /// \brief Search for packages prefixed with this "prefix"
   std::string Prefix;
 };

nixd/lib/Controller/AST.cpp

@@ -124,12 +124,31 @@ bool nixd::havePackageScope(const Node &N, const VariableLookupAnalysis &VLA,
       continue;
 
     // Hardcoded "pkgs", even more stupid.
-    if (static_cast<const ExprVar &>(*WithBody).id().name() == "pkgs")
+    if (static_cast<const ExprVar &>(*WithBody).id().name() == idioms::Pkgs)
       return true;
   }
   return false;
 }
 
+nixd::Selector nixd::mkSelector(const nixf::AttrPath &AP,
+                                Selector BaseSelector) {
+  const auto &Names = AP.names();
+  for (const auto &Name : Names) {
+    if (!Name->isStatic())
+      throw DynamicNameException();
+    BaseSelector.emplace_back(Name->staticName());
+  }
+  return BaseSelector;
+}
+
+nixd::Selector nixd::mkSelector(const nixf::ExprSelect &Select,
+                                nixd::Selector BaseSelector) {
+  if (Select.path())
+    return nixd::mkSelector(*static_cast<const nixf::AttrPath *>(Select.path()),
+                            std::move(BaseSelector));
+  return BaseSelector;
+}
+
 std::pair<std::vector<std::string>, std::string>
 nixd::getScopeAndPrefix(const Node &N, const ParentMapAnalysis &PM) {
   if (N.kind() != Node::NK_Identifer)

nixd/lib/Controller/AST.h

@@ -1,11 +1,29 @@
 /// \file
 /// \brief This file declares some common analysis (tree walk) on the AST.
 
+#include "nixd/Protocol/AttrSet.h"
+
 #include <nixf/Sema/ParentMap.h>
 #include <nixf/Sema/VariableLookup.h>
 
 namespace nixd {
 
+namespace idioms {
+
+/// \brief Hardcoded name for "pkgs.xxx", or "with pkgs;"
+///
+/// Assume that the value of this variable have the same structure with `import
+/// nixpkgs {}
+constexpr inline std::string_view Pkgs = "pkgs";
+
+/// \brief Hardcoded name for nixpkgs "lib"
+///
+/// Assume that the value of this variable is "nixpkgs lib".
+/// e.g. lib.genAttrs.
+constexpr inline std::string_view Lib = "lib";
+
+} // namespace idioms
+
 /// \brief Search up until there are some node associated with "EnvNode".
 [[nodiscard]] const nixf::EnvNode *
 upEnv(const nixf::Node &Desc, const nixf::VariableLookupAnalysis &VLA,
@@ -29,6 +47,16 @@ upEnv(const nixf::Node &Desc, const nixf::VariableLookupAnalysis &VLA,
 std::pair<std::vector<std::string>, std::string>
 getScopeAndPrefix(const nixf::Node &N, const nixf::ParentMapAnalysis &PM);
 
+/// \brief The attrpath has a dynamic name, thus it cannot be trivially
+/// transformed to "static" selector.
+struct DynamicNameException : std::exception {};
+
+/// \brief Construct a nixd::Selector from \p AP.
+Selector mkSelector(const nixf::AttrPath &AP, Selector BaseSelector);
+
+/// \brief Construct a nixd::Selector from \p Select.
+Selector mkSelector(const nixf::ExprSelect &Select, Selector BaseSelector);
+
 enum class FindAttrPathResult {
   OK,
   Inherit,

nixd/lib/Controller/Completion.cpp

@@ -14,6 +14,7 @@
 
 #include <semaphore>
 #include <set>
+#include <unordered_set>
 #include <utility>
 
 using namespace nixd;
@@ -123,7 +124,7 @@ class NixpkgsCompletionProvider {
   }
 
   /// \brief Ask nixpkgs provider, give us a list of names. (thunks)
-  void completePackages(std::vector<std::string> Scope, std::string Prefix,
+  void completePackages(const AttrPathCompleteParams &Params,
                         std::vector<CompletionItem> &Items) {
     std::binary_semaphore Ready(0);
     std::vector<std::string> Names;
@@ -138,12 +139,11 @@ class NixpkgsCompletionProvider {
       Ready.release();
     };
     // Send request.
-    AttrPathCompleteParams Params{std::move(Scope), std::move(Prefix)};
     NixpkgsClient.attrpathComplete(Params, std::move(OnReply));
     Ready.acquire();
     // Now we have "Names", use these to fill "Items".
     for (const auto &Name : Names) {
-      if (Name.starts_with(Prefix)) {
+      if (Name.starts_with(Params.Prefix)) {
         addItem(Items, CompletionItem{
                            .label = Name,
                            .kind = CompletionItemKind::Field,
@@ -265,6 +265,98 @@ void completeAttrName(const std::vector<std::string> &Scope,
   }
 }
 
+void completeAttrPath(const Node &N, const ParentMapAnalysis &PM,
+                      std::mutex &OptionsLock, Controller::OptionMapTy &Options,
+                      bool Snippets,
+                      std::vector<lspserver::CompletionItem> &Items) {
+  std::vector<std::string> Scope;
+  using PathResult = FindAttrPathResult;
+  auto R = findAttrPath(N, PM, Scope);
+  if (R == PathResult::OK) {
+    // Construct request.
+    std::string Prefix = Scope.back();
+    Scope.pop_back();
+    {
+      std::lock_guard _(OptionsLock);
+      completeAttrName(Scope, Prefix, Options, Snippets, Items);
+    }
+  }
+}
+
+void completeVarName(const VariableLookupAnalysis &VLA,
+                     const ParentMapAnalysis &PM, const nixf::Node &N,
+                     AttrSetClient &Client, std::vector<CompletionItem> &List) {
+  VLACompletionProvider VLAP(VLA);
+  VLAP.complete(N, List, PM);
+  if (havePackageScope(N, VLA, PM)) {
+    // Append it with nixpkgs completion
+    // FIXME: handle null nixpkgsClient()
+    NixpkgsCompletionProvider NCP(Client);
+    auto [Scope, Prefix] = getScopeAndPrefix(N, PM);
+    NCP.completePackages({Scope, Prefix}, List);
+  }
+}
+
+AttrPathCompleteParams mkParams(nixd::Selector Sel, bool IsComplete) {
+  if (IsComplete) {
+    return {
+        .Scope = std::move(Sel),
+        .Prefix = "",
+    };
+  }
+  std::string Back = std::move(Sel.back());
+  Sel.pop_back();
+  return {
+      .Scope = Sel,
+      .Prefix = std::move(Back),
+  };
+}
+
+/// \brief Complete a "select" expression.
+/// \param IsComplete Whether or not the last element of the selector is
+/// effectively incomplete.
+/// e.g.
+///      - incomplete: `lib.gen|`
+///      - complete:   `lib.attrset.|`
+void completeSelect(const nixf::ExprSelect &Select, AttrSetClient &Client,
+                    bool IsComplete, std::vector<CompletionItem> &List) {
+  // The base expr for selecting.
+  const nixf::Expr &BaseExpr = Select.expr();
+
+  // Determine that the name is one of special names interesting
+  // for nix language. If it is not a simple variable, skip this
+  // case.
+  if (BaseExpr.kind() != Node::NK_ExprVar) {
+    return;
+  }
+
+  const auto &Var = static_cast<const nixf::ExprVar &>(BaseExpr);
+
+  // See if the variable matches some idioms name we alreay know.
+  std::unordered_set<std::string_view> S{idioms::Pkgs, idioms::Lib};
+  auto It = S.find(Var.id().name());
+
+  // Unknown name, cannot deal with it.
+  if (It == S.end())
+    return;
+
+  // Ask nixpkgs provider to get idioms completion.
+  NixpkgsCompletionProvider NCP(Client);
+
+  // Construct the scope & prefix suitable for this "select".
+  Selector BaseSelector = It == S.find(idioms::Lib)
+                              ? Selector{std::string(idioms::Lib)}
+                              : Selector{};
+  try {
+    Selector Sel = mkSelector(Select, std::move(BaseSelector));
+    NCP.completePackages(mkParams(Sel, IsComplete), List);
+  } catch (DynamicNameException &DE) {
+    lspserver::log(
+        "completion/select: skip because attribute path contains dynamic attr");
+    return;
+  }
+}
+
 } // namespace
 
 void Controller::onCompletion(const CompletionParams &Params,
@@ -283,38 +375,53 @@ void Controller::onCompletion(const CompletionParams &Params,
           Reply(CompletionList{});
           return;
         }
-        CompletionList List;
-        try {
-          const ParentMapAnalysis &PM = *TU->parentMap();
-          std::vector<std::string> Scope;
-          using PathResult = FindAttrPathResult;
-          auto R = findAttrPath(*Desc, PM, Scope);
-          if (R == PathResult::OK) {
-            // Construct request.
-            std::string Prefix = Scope.back();
-            Scope.pop_back();
-            {
-              std::lock_guard _(OptionsLock);
-              completeAttrName(Scope, Prefix, Options,
+        const nixf::Node &N = *Desc;
+        const ParentMapAnalysis &PM = *TU->parentMap();
+        const Node *MaybeUpExpr = PM.upExpr(N);
+        if (!MaybeUpExpr) {
+          // If there is no concrete expression containing the cursor
+          // Reply an empty list.
+          Reply(CompletionList{});
+          return;
+        }
+        // Otherwise, construct the completion list from a set of providers.
+        const Node &UpExpr = *MaybeUpExpr;
+        Reply([&]() -> CompletionList {
+          CompletionList List;
+          try {
+            switch (UpExpr.kind()) {
+            // In these cases, assume the cursor have "variable" scoping.
+            case Node::NK_ExprWith:
+            case Node::NK_ExprList:
+            case Node::NK_ExprVar: {
+              const VariableLookupAnalysis &VLA = *TU->variableLookup();
+              completeVarName(VLA, PM, N, *nixpkgsClient(), List.items);
+              break;
+            }
+            // A "select" expression. e.g.
+            // foo.a|
+            // foo.|
+            // foo.a.bar|
+            case Node::NK_ExprSelect: {
+              const auto &Select =
+                  static_cast<const nixf::ExprSelect &>(UpExpr);
+              completeSelect(Select, *nixpkgsClient(), N.kind() == Node::NK_Dot,
+                             List.items);
+              break;
+            }
+            case Node::NK_ExprAttrs: {
+              completeAttrPath(N, PM, OptionsLock, Options,
                                ClientCaps.CompletionSnippets, List.items);
+              break;
             }
-          } else {
-            const VariableLookupAnalysis &VLA = *TU->variableLookup();
-            VLACompletionProvider VLAP(VLA);
-            VLAP.complete(*Desc, List.items, PM);
-            if (havePackageScope(*Desc, VLA, PM)) {
-              // Append it with nixpkgs completion
-              // FIXME: handle null nixpkgsClient()
-              NixpkgsCompletionProvider NCP(*nixpkgsClient());
-              auto [Scope, Prefix] = getScopeAndPrefix(*Desc, PM);
-              NCP.completePackages(Scope, Prefix, List.items);
+            default:
+              break;
             }
+          } catch (ExceedSizeError &Err) {
+            List.isIncomplete = true;
           }
-          // Next, add nixpkgs provided names.
-        } catch (ExceedSizeError &Err) {
-          List.isIncomplete = true;
-        }
-        Reply(std::move(List));
+          return List;
+        }());
       }
     }
   };

nixd/tools/nixd/test/completion-select-lib.md

@@ -0,0 +1,77 @@
+# RUN: nixd --lit-test \
+# RUN: --nixpkgs-expr="{ lib.hello.meta.description = \"Very Nice\";  }" \
+# RUN: < %s | FileCheck %s
+
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "method":"textDocument/didOpen",
+   "params":{
+      "textDocument":{
+         "uri":"file:///completion.nix",
+         "languageId":"nix",
+         "version":1,
+         "text":"lib.hel"
+      }
+   }
+}
+```
+
+```json
+{
+    "jsonrpc": "2.0",
+    "id": 1,
+    "method": "textDocument/completion",
+    "params": {
+        "textDocument": {
+            "uri": "file:///completion.nix"
+        },
+        "position": {
+            "line": 0,
+            "character": 6
+        },
+        "context": {
+            "triggerKind": 1
+        }
+    }
+}
+```
+
+```
+     CHECK:    "isIncomplete": false,
+CHECK-NEXT:    "items": [
+CHECK-NEXT:      {
+CHECK-NEXT:        "data": "{\"Prefix\":\"hel\",\"Scope\":[\"lib\"]}",
+CHECK-NEXT:        "kind": 5,
+CHECK-NEXT:        "label": "hello",
+CHECK-NEXT:        "score": 0
+CHECK-NEXT:      }
+CHECK-NEXT:    ]
+```
+
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```