Also display suggestions for the commands using the eval cache

Make `nix build .#nix-armv8l-linux` work for example

2 files changed, 32 insertions, 11 deletions

diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 00d0749f9..188223957 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -406,6 +406,16 @@ Value & AttrCursor::forceValue()
     return v;
 }
 
+Suggestions AttrCursor::getSuggestionsForAttr(Symbol name)
+{
+    auto attrNames = getAttrs();
+    std::set<std::string> strAttrNames;
+    for (auto & name : attrNames)
+        strAttrNames.insert(std::string(name));
+
+    return Suggestions::bestMatches(strAttrNames, name);
+}
+
 std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErrors)
 {
     if (root->db) {
@@ -446,6 +456,11 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
         return nullptr;
         //throw TypeError("'%s' is not an attribute set", getAttrPathStr());
 
+    for (auto & attr : *v.attrs) {
+        if (root->db)
+            root->db->setPlaceholder({cachedValue->first, attr.name});
+    }
+
     auto attr = v.attrs->get(name);
 
     if (!attr) {
@@ -464,7 +479,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name, bool forceErro
         cachedValue2 = {root->db->setPlaceholder({cachedValue->first, name}), placeholder_t()};
     }
 
-    return std::make_shared<AttrCursor>(
+    return make_ref<AttrCursor>(
         root, std::make_pair(shared_from_this(), name), attr->value, std::move(cachedValue2));
 }
 
@@ -473,27 +488,31 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(std::string_view name)
     return maybeGetAttr(root->state.symbols.create(name));
 }
 
-std::shared_ptr<AttrCursor> AttrCursor::getAttr(Symbol name, bool forceErrors)
+ref<AttrCursor> AttrCursor::getAttr(Symbol name, bool forceErrors)
 {
     auto p = maybeGetAttr(name, forceErrors);
     if (!p)
         throw Error("attribute '%s' does not exist", getAttrPathStr(name));
-    return p;
+    return ref(p);
 }
 
-std::shared_ptr<AttrCursor> AttrCursor::getAttr(std::string_view name)
+ref<AttrCursor> AttrCursor::getAttr(std::string_view name)
 {
     return getAttr(root->state.symbols.create(name));
 }
 
-std::shared_ptr<AttrCursor> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force)
+OrSuggestions<ref<AttrCursor>> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force)
 {
     auto res = shared_from_this();
     for (auto & attr : attrPath) {
-        res = res->maybeGetAttr(attr, force);
-        if (!res) return {};
+        auto child = res->maybeGetAttr(attr, force);
+        if (!child) {
+            auto suggestions = res->getSuggestionsForAttr(attr);
+            return OrSuggestions<ref<AttrCursor>>::failed(suggestions);
+        }
+        res = child;
     }
-    return res;
+    return ref(res);
 }
 
 std::string AttrCursor::getString()
diff --git a/src/libexpr/eval-cache.hh b/src/libexpr/eval-cache.hh
index 43b34ebcb..40f1d4ffc 100644
--- a/src/libexpr/eval-cache.hh
+++ b/src/libexpr/eval-cache.hh
@@ -94,15 +94,17 @@ public:
 
     std::string getAttrPathStr(Symbol name) const;
 
+    Suggestions getSuggestionsForAttr(Symbol name);
+
     std::shared_ptr<AttrCursor> maybeGetAttr(Symbol name, bool forceErrors = false);
 
     std::shared_ptr<AttrCursor> maybeGetAttr(std::string_view name);
 
-    std::shared_ptr<AttrCursor> getAttr(Symbol name, bool forceErrors = false);
+    ref<AttrCursor> getAttr(Symbol name, bool forceErrors = false);
 
-    std::shared_ptr<AttrCursor> getAttr(std::string_view name);
+    ref<AttrCursor> getAttr(std::string_view name);
 
-    std::shared_ptr<AttrCursor> findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force = false);
+    OrSuggestions<ref<AttrCursor>> findAlongAttrPath(const std::vector<Symbol> & attrPath, bool force = false);
 
     std::string getString();