libexpr: Make positionToDocComment thread-safe

xokdvium · xokdvium · commit ff022d829216 · 2026-03-14T15:09:12.000+03:00
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
@@ -303,6 +303,7 @@ EvalState::EvalState(
     , srcToStore(make_ref<decltype(srcToStore)::element_type>())
     , importResolutionCache(make_ref<decltype(importResolutionCache)::element_type>())
     , fileEvalCache(make_ref<decltype(fileEvalCache)::element_type>())
+    , positionToDocComment(make_ref<decltype(positionToDocComment)::element_type>())
     , regexCache(makeRegexCache())
 #if NIX_USE_BOEHMGC
     , baseEnvP(std::allocate_shared<Env *>(traceable_allocator<Env *>(), &mem.allocEnv(BASE_ENV_SIZE)))
@@ -3345,19 +3346,21 @@ Expr * EvalState::parse(
     const SourcePath & basePath,
     const std::shared_ptr<StaticEnv> & staticEnv)
 {
-    DocCommentMap tmpDocComments; // Only used when not origin is not a SourcePath
-    DocCommentMap * docComments = &tmpDocComments;
+    auto tmpDocComments = make_ref<DocCommentMap>();
 
-    if (auto sourcePath = std::get_if<SourcePath>(&origin)) {
-        auto [it, _] = positionToDocComment.try_emplace(*sourcePath);
-        docComments = &it->second;
-    }
-
-    auto result =
-        parseExprFromBuf(text, length, origin, basePath, mem.exprs, symbols, settings, positions, *docComments, rootFS);
+    auto result = parseExprFromBuf(
+        text, length, origin, basePath, mem.exprs, symbols, settings, positions, *tmpDocComments, rootFS);
 
     result->bindVars(*this, staticEnv);
 
+    if (auto sourcePath = std::get_if<SourcePath>(&origin))
+        /* A single file might appear multiple times in PosTable if it's
+           parsed by scopedImport. If we are the first then emplace into the map, otherwise
+           copy our positions into the existing map. */
+        positionToDocComment->emplace_or_visit(*sourcePath, tmpDocComments, [&tmpDocComments](auto & kv) {
+            kv.second->insert(tmpDocComments->begin(), tmpDocComments->end());
+        });
+
     return result;
 }
 
@@ -3368,20 +3371,22 @@ ExprAttrs * EvalState::parseReplBindings(
     const SourcePath & basePath,
     const std::shared_ptr<StaticEnv> & staticEnv)
 {
-    DocCommentMap tmpDocComments;
-    DocCommentMap * docComments = &tmpDocComments;
-
-    if (auto sourcePath = std::get_if<SourcePath>(&origin)) {
-        auto [it, _] = positionToDocComment.try_emplace(*sourcePath);
-        docComments = &it->second;
-    }
+    auto tmpDocComments = make_ref<DocCommentMap>();
 
     auto bindings = parseReplBindingsFromBuf(
-        text, length, origin, basePath, mem.exprs, symbols, settings, positions, *docComments, rootFS);
+        text, length, origin, basePath, mem.exprs, symbols, settings, positions, *tmpDocComments, rootFS);
     assert(bindings);
 
     bindings->bindVars(*this, staticEnv);
 
+    if (auto sourcePath = std::get_if<SourcePath>(&origin))
+        /* A single file might appear multiple times in PosTable if it's
+           parsed by scopedImport. If we are the first then emplace into the map, otherwise
+           copy our positions into the existing map. */
+        positionToDocComment->emplace_or_visit(*sourcePath, tmpDocComments, [&tmpDocComments](auto & kv) {
+            kv.second->insert(tmpDocComments->begin(), tmpDocComments->end());
+        });
+
     return bindings;
 }
 
@@ -3392,14 +3397,12 @@ DocComment EvalState::getDocCommentForPos(PosIdx pos)
     if (!path)
         return {};
 
-    auto table = positionToDocComment.find(*path);
-    if (table == positionToDocComment.end())
-        return {};
-
-    auto it = table->second.find(pos);
-    if (it == table->second.end())
-        return {};
-    return it->second;
+    DocComment result;
+    positionToDocComment->visit(*path, [&](const auto & kv) {
+        if (auto it = kv.second->find(pos); it != kv.second->end())
+            result = it->second;
+    });
+    return result;
 }
 
 std::string ExternalValueBase::coerceToString(
diff --git a/src/libexpr/include/nix/expr/eval.hh b/src/libexpr/include/nix/expr/eval.hh
@@ -484,7 +484,7 @@ private:
      * Associate source positions of certain AST nodes with their preceding doc comment, if they have one.
      * Grouped by file.
      */
-    boost::unordered_flat_map<SourcePath, DocCommentMap> positionToDocComment;
+    const ref<boost::concurrent_flat_map<SourcePath, ref<DocCommentMap>>> positionToDocComment;
 
     LookupPath lookupPath;
 
