Complete flake inputs for all given flakes

Allow `nix build flake1 flake2 --update-input <Tab>` to complete the
inputs of both flakes.

Also do tilde expansion so that `nix build ~/flake --update-input <Tab>`
works.

src/libcmd/command.hh

@@ -79,8 +79,10 @@ struct MixFlakeOptions : virtual Args, EvalCommand
 
     MixFlakeOptions();
 
-    virtual std::optional<FlakeRef> getFlakeRefForCompletion()
+    virtual std::vector<std::string> getFlakesForCompletion()
     { return {}; }
+
+    void completeFlakeInput(std::string_view prefix);
 };
 
 struct SourceExprCommand : virtual Args, MixFlakeOptions
@@ -119,7 +121,7 @@ struct InstallablesCommand : virtual Args, SourceExprCommand
 
     virtual bool useDefaultInstallables() { return true; }
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override;
+    std::vector<std::string> getFlakesForCompletion() override;
 
 private:
 
@@ -135,9 +137,9 @@ struct InstallableCommand : virtual Args, SourceExprCommand
 
     void prepare() override;
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override
+    std::vector<std::string> getFlakesForCompletion() override
     {
-        return parseFlakeRefWithFragment(_installable, absPath(".")).first;
+        return {_installable};
     }
 
 private:

src/libcmd/installables.cc

@@ -23,15 +23,16 @@
 
 namespace nix {
 
-void completeFlakeInputPath(
-    ref<EvalState> evalState,
-    const FlakeRef & flakeRef,
-    std::string_view prefix)
+void MixFlakeOptions::completeFlakeInput(std::string_view prefix)
 {
+    auto evalState = getEvalState();
+    for (auto & flakeRefS : getFlakesForCompletion()) {
+        auto flakeRef = parseFlakeRefWithFragment(expandTilde(flakeRefS), absPath(".")).first;
         auto flake = flake::getFlake(*evalState, flakeRef, true);
         for (auto & input : flake.inputs)
             if (hasPrefix(input.first, prefix))
                 completions->add(input.first);
+    }
 }
 
 MixFlakeOptions::MixFlakeOptions()
@@ -86,8 +87,7 @@ MixFlakeOptions::MixFlakeOptions()
             lockFlags.inputUpdates.insert(flake::parseInputPath(s));
         }},
         .completer = {[&](size_t, std::string_view prefix) {
-            if (auto flakeRef = getFlakeRefForCompletion())
-                completeFlakeInputPath(getEvalState(), *flakeRef, prefix);
+            completeFlakeInput(prefix);
         }}
     });
 
@@ -103,12 +103,10 @@ MixFlakeOptions::MixFlakeOptions()
                 parseFlakeRef(flakeRef, absPath("."), true));
         }},
         .completer = {[&](size_t n, std::string_view prefix) {
-            if (n == 0) {
-                if (auto flakeRef = getFlakeRefForCompletion())
-                    completeFlakeInputPath(getEvalState(), *flakeRef, prefix);
-            } else if (n == 1) {
+            if (n == 0)
+                completeFlakeInput(prefix);
+            else if (n == 1)
                 completeFlakeRef(getEvalState()->store, prefix);
-            }
         }}
     });
 
@@ -1043,14 +1041,14 @@ void InstallablesCommand::prepare()
     installables = parseInstallables(getStore(), _installables);
 }
 
-std::optional<FlakeRef> InstallablesCommand::getFlakeRefForCompletion()
+std::vector<std::string> InstallablesCommand::getFlakesForCompletion()
 {
     if (_installables.empty()) {
         if (useDefaultInstallables())
-            return parseFlakeRefWithFragment(".", absPath(".")).first;
+            return {"."};
         return {};
     }
-    return parseFlakeRefWithFragment(_installables.front(), absPath(".")).first;
+    return _installables;
 }
 
 InstallableCommand::InstallableCommand(bool supportReadOnlyMode)

src/nix/flake.cc

@@ -50,9 +50,9 @@ public:
         return flake::lockFlake(*getEvalState(), getFlakeRef(), lockFlags);
     }
 
-    std::optional<FlakeRef> getFlakeRefForCompletion() override
+    std::vector<std::string> getFlakesForCompletion() override
     {
-        return getFlakeRef();
+        return {flakeUrl};
     }
 };