style(3p/nix): Enforce braces around loops and conditionals r/767

This change was generated with:

  fd -e cc -e hh | xargs -I{} clang-tidy {} -p ~/projects/nix-build/ \
    --checks='-*,readability-braces-around-statements' --fix \
    -fix-errors

Some manual fixes were applied because some convoluted unbraced
statements couldn't be untangled by clang-tidy.

This commit still includes invalid files, but I decided to clean them
up in a subsequent commit so that it becomes more obvious where
clang-tidy failed. Maybe this will allow for a bug-report to
clang-tidy.

1 files changed, 7 insertions, 3 deletions

diff --git a/third_party/nix/src/nix-instantiate/nix-instantiate.cc b/third_party/nix/src/nix-instantiate/nix-instantiate.cc
index 15b07a8545..df97f23ef9 100644
--- a/third_party/nix/src/nix-instantiate/nix-instantiate.cc
+++ b/third_party/nix/src/nix-instantiate/nix-instantiate.cc
@@ -147,7 +147,9 @@ static int _main(int argc, char** argv) {
 
     initPlugins();
 
-    if (evalOnly && !wantsReadWrite) settings.readOnlyMode = true;
+    if (evalOnly && !wantsReadWrite) {
+      settings.readOnlyMode = true;
+    }
 
     auto store = openStore();
 
@@ -171,8 +173,10 @@ static int _main(int argc, char** argv) {
       Expr* e = state->parseStdin();
       processExpr(*state, attrPaths, parseOnly, strict, autoArgs, evalOnly,
                   outputKind, xmlOutputSourceLocation, e);
-    } else if (files.empty() && !fromArgs)
-      files.push_back("./default.nix");
+    } else {
+      if
+    }
+    (files.empty() && !fromArgs) files.push_back("./default.nix");
 
     for (auto& i : files) {
       Expr* e = fromArgs