util/error: Document addTrace params

... and rename e -> pos. That was weird.

Author: roberth

src/libutil/include/nix/util/error.hh

@@ -192,13 +192,23 @@ public:
         err.traces.push_front(trace);
     }
 
+    /**
+     * @param pos Nullable `shared_ptr<Pos>`
+     * @param fs Format string, see `HintFmt`
+     * @param args... Format string arguments.
+     */
     template<typename... Args>
-    void addTrace(std::shared_ptr<const Pos> && e, std::string_view fs, const Args &... args)
+    void addTrace(std::shared_ptr<const Pos> && pos, std::string_view fs, const Args &... args)
     {
-        addTrace(std::move(e), HintFmt(std::string(fs), args...));
+        addTrace(std::move(pos), HintFmt(std::string(fs), args...));
     }
 
-    void addTrace(std::shared_ptr<const Pos> && e, HintFmt hint, TracePrint print = TracePrint::Default);
+    /**
+     * @param pos Nullable `shared_ptr<Pos>`
+     * @param hint Formatted error message
+     * @param print Optional, whether to always print (e.g. `addErrorContext`)
+     */
+    void addTrace(std::shared_ptr<const Pos> && pos, HintFmt hint, TracePrint print = TracePrint::Default);
 
     bool hasTrace() const
     {