nixd: add hover support

lib/nixd/include/nixd/CallbackExpr.h

@@ -19,6 +19,7 @@ using ExprCallback =
     static Callback##EXPR *create(ASTContext &Cxt, const nix::EXPR &E,         \
                                   ExprCallback ECB);                           \
     void eval(nix::EvalState &State, nix::Env &Env, nix::Value &V) override;   \
+    std::string getName();                                                     \
   };
 #include "NixASTNodes.inc"
 #undef NIX_EXPR

lib/nixd/include/nixd/Expr.h

@@ -66,4 +66,14 @@ template <class Derived> struct RecursiveASTVisitor {
 #undef DEF_TRAVERSE_TYPE
 #undef TRY_TO_TRAVERSE
 #undef TRY_TO
+
+inline const char *getExprName(nix::Expr *E) {
+#define NIX_EXPR(EXPR)                                                         \
+  if (dynamic_cast<const nix::EXPR *>(E)) {                                    \
+    return #EXPR;                                                              \
+  }
+#include "NixASTNodes.inc"
+#undef NIX_EXPR
+}
+
 } // namespace nixd

lib/nixd/include/nixd/Server.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "nixd/EvalDraftStore.h"
+
 #include "lspserver/Connection.h"
 #include "lspserver/DraftStore.h"
 #include "lspserver/Function.h"
@@ -33,7 +35,8 @@ bool fromJSON(const llvm::json::Value &Params, InstallableConfigurationItem &R,
 /// The server instance, nix-related language features goes here
 class Server : public lspserver::LSPServer {
 
-  lspserver::DraftStore DraftMgr;
+  EvalDraftStore DraftMgr;
+  boost::asio::thread_pool Pool;
 
   lspserver::ClientCapabilities ClientCaps;
 
@@ -64,6 +67,7 @@ class Server : public lspserver::LSPServer {
          std::unique_ptr<lspserver::OutboundPort> Out)
       : LSPServer(std::move(In), std::move(Out)) {
     Registry.addMethod("initialize", this, &Server::onInitialize);
+    Registry.addMethod("textDocument/hover", this, &Server::onHover);
     Registry.addNotification("initialized", this, &Server::onInitialized);
 
     // Text Document Synchronization
@@ -82,6 +86,8 @@ class Server : public lspserver::LSPServer {
             "workspace/configuration");
   }
 
+  ~Server() override { Pool.join(); }
+
   void fetchConfig();
 
   void onInitialize(const lspserver::InitializeParams &,
@@ -104,6 +110,8 @@ class Server : public lspserver::LSPServer {
       const lspserver::DidChangeConfigurationParams &) {
     fetchConfig();
   }
+  void onHover(const lspserver::TextDocumentPositionParams &,
+               lspserver::Callback<llvm::json::Value>);
 };
 
 }; // namespace nixd

lib/nixd/src/EvalDraftStore.cpp

@@ -57,8 +57,8 @@ void EvalDraftStore::withEvaluation(
           Forest.insert({ActiveFile, nix::make_ref<EvalAST>(FileAST)});
           Forest.at(ActiveFile)->preparePositionLookup(*State);
           Forest.at(ActiveFile)->injectAST(*State, ActiveFile);
-        } catch (const nix::ParseError &) {
-          // Ignore parsing errors, because workspace file might be incomplete.
+        } catch (const nix::Error &) {
+          // Ignore caching errors, because workspace file might be incomplete.
         }
       }
 

lib/nixd/src/Server.cpp

@@ -1,6 +1,8 @@
 #include "nixd/Server.h"
 #include "nixd/Diagnostic.h"
+#include "nixd/Expr.h"
 
+#include "lspserver/Logger.h"
 #include "lspserver/Path.h"
 #include "lspserver/Protocol.h"
 
@@ -11,8 +13,16 @@
 
 #include <nix/eval.hh>
 #include <nix/store-api.hh>
+#include <nix/util.hh>
 
+#include <exception>
 #include <filesystem>
+#include <optional>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <variant>
+
 namespace fs = std::filesystem;
 namespace nixd {
 
@@ -50,6 +60,7 @@ void Server::onInitialize(const lspserver::InitializeParams &InitializeParams,
            {"change", (int)lspserver::TextDocumentSyncKind::Incremental},
            {"save", true},
        }},
+      {"hoverProvider", true},
   };
 
   llvm::json::Object Result{
@@ -128,8 +139,8 @@ void Server::publishStandaloneDiagnostic(lspserver::URIForFile Uri,
   auto NixState = std::make_unique<nix::EvalState>(nix::Strings{}, NixStore);
   try {
     fs::path Path = Uri.file().str();
-    auto *E =
-        NixState->parseExprFromString(std::move(Content), Path.remove_filename());
+    auto *E = NixState->parseExprFromString(std::move(Content),
+                                            Path.remove_filename());
     nix::Value V;
     NixState->eval(E, V);
   } catch (const nix::Error &PE) {
@@ -143,4 +154,73 @@ void Server::publishStandaloneDiagnostic(lspserver::URIForFile Uri,
       .uri = Uri, .diagnostics = {}, .version = LSPVersion});
 }
 
+void Server::onHover(const lspserver::TextDocumentPositionParams &Paras,
+                     lspserver::Callback<llvm::json::Value> Reply) {
+  std::string HoverFile = Paras.textDocument.uri.file().str();
+
+  // Helper lambda that retrieve installable cmdline
+  auto GetInstallableFromConfig = [&]() {
+    if (auto Installable = Config.installable) {
+      auto ConfigArgs = Installable->args;
+      lspserver::log("using client specified installable: [{0}] {1}",
+                     llvm::iterator_range(ConfigArgs.begin(), ConfigArgs.end()),
+                     Installable->installable);
+      return std::tuple{nix::Strings(ConfigArgs.begin(), ConfigArgs.end()),
+                        Installable->installable};
+    }
+    // Fallback to current file otherwise.
+    return std::tuple{nix::Strings{"--file", HoverFile}, std::string{""}};
+  };
+
+  auto [CommandLine, Installable] = GetInstallableFromConfig();
+
+  DraftMgr.withEvaluation(
+      Pool, CommandLine, Installable,
+      [=, Reply = std::move(Reply)](
+          std::variant<std::exception *,
+                       nix::ref<EvalDraftStore::EvaluationResult>>
+              EvalResult) mutable {
+        auto ActionOnResult =
+            [&](const nix::ref<EvalDraftStore::EvaluationResult> &Result) {
+              auto Forest = Result->EvalASTForest;
+              try {
+                auto AST = Forest.at(HoverFile);
+                auto *Node = AST->lookupPosition(Paras.position);
+                const auto *ExprName = getExprName(Node);
+                std::string HoverText;
+                try {
+                  auto Value = AST->getValue(Node);
+                  std::stringstream Res{};
+                  Value.print(Result->State->symbols, Res);
+                  HoverText = llvm::formatv("## {0} \n Value: `{1}`", ExprName,
+                                            Res.str());
+                } catch (const std::out_of_range &) {
+                  // No such value, just reply dummy item
+                  std::stringstream NodeOut;
+                  Node->show(Result->State->symbols, NodeOut);
+                  lspserver::vlog("no associated value on node {0}!",
+                                  NodeOut.str());
+                  HoverText = llvm::formatv("`{0}`", ExprName);
+                }
+                Reply(lspserver::Hover{{
+                                           lspserver::MarkupKind::Markdown,
+                                           HoverText,
+                                       },
+                                       std::nullopt});
+              } catch (const std::out_of_range &) {
+                // Probably out of range in Forest.at
+                // Ignore this expression, and reply dummy value.
+                Reply(lspserver::Hover{{}, std::nullopt});
+              }
+            };
+        auto ActionOnExcept = [&](std::exception *Except) {
+          // TODO: publish evaluation diagnostic
+          lspserver::log("evaluation error: {0}", Except->what());
+          Reply(lspserver::Hover{{}, std::nullopt});
+        };
+
+        std::visit(nix::overloaded{ActionOnResult, ActionOnExcept}, EvalResult);
+      });
+}
+
 } // namespace nixd

tools/nixd/test/hover-eval-error.md

@@ -0,0 +1,101 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+File #1:
+
+```nix
+let
+  pkgs = {
+    a = 1;
+  };
+in
+with pkgs;
+
+a
+```
+
+```json
+{
+   "jsonrpc":"2.0",
+   "method":"textDocument/didOpen",
+   "params":{
+      "textDocument":{
+         "uri":"file:///with.nix",
+         "languageId":"nix",
+         "version":1,
+         "text":"let\n  pkgs = {\n    a = 1;\n  };\nin\nwith pkgs;\n\na\n\n"
+      }
+   }
+}
+```
+
+File #2:
+
+
+```json
+{
+   "jsonrpc":"2.0",
+   "method":"textDocument/didOpen",
+   "params":{
+      "textDocument":{
+         "uri":"file:///parse-error.nix",
+         "languageId":"nix",
+         "version":1,
+         "text":"let x = 1; in y"
+      }
+   }
+}
+```
+
+<-- textDocument/hover
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/hover",
+   "params":{
+      "textDocument":{
+         "uri":"file:///with.nix"
+      },
+      "position":{
+         "line":1,
+         "character":2
+      }
+   }
+}
+```
+
+```
+     CHECK:  "id": 2,
+CHECK-NEXT:  "jsonrpc": "2.0",
+CHECK-NEXT:  "result": {
+CHECK-NEXT:    "contents": {
+CHECK-NEXT:      "kind": "markdown",
+CHECK-NEXT:      "value": "`ExprAttrs`"
+CHECK-NEXT:    }
+CHECK-NEXT:  }
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```

tools/nixd/test/hover-no-value.md

@@ -0,0 +1,84 @@
+# RUN: nixd --lit-test < %s | FileCheck %s
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+
+<-- textDocument/didOpen
+
+Testing this nix file:
+
+```nix
+let
+  pkgs = {
+    a = 1;
+  };
+in
+with pkgs;
+
+a
+```
+
+```json
+{
+   "jsonrpc":"2.0",
+   "method":"textDocument/didOpen",
+   "params":{
+      "textDocument":{
+         "uri":"file:///with.nix",
+         "languageId":"nix",
+         "version":1,
+         "text":"let\n  pkgs = {\n    a = 1;\n  };\nin\nwith pkgs;\n\na\n\n"
+      }
+   }
+}
+```
+
+
+<-- textDocument/hover
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":2,
+   "method":"textDocument/hover",
+   "params":{
+      "textDocument":{
+         "uri":"file:///with.nix"
+      },
+      "position":{
+         "line":1,
+         "character":2
+      }
+   }
+}
+```
+
+```
+     CHECK:  "id": 2,
+CHECK-NEXT:  "jsonrpc": "2.0",
+CHECK-NEXT:  "result": {
+CHECK-NEXT:    "contents": {
+CHECK-NEXT:      "kind": "markdown",
+CHECK-NEXT:      "value": "`ExprAttrs`"
+CHECK-NEXT:    }
+CHECK-NEXT:  }
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```