Merge pull request #13310 from xokdvium/cleanup-position

libutil: Use `std::shared_ptr<const Pos>` and simplify `Pos` class constructors

src/libutil/error.cc

@@ -13,7 +13,7 @@
 
 namespace nix {
 
-void BaseError::addTrace(std::shared_ptr<Pos> && e, HintFmt hint, TracePrint print)
+void BaseError::addTrace(std::shared_ptr<const Pos> && e, HintFmt hint, TracePrint print)
 {
     err.traces.push_front(Trace { .pos = std::move(e), .hint = hint, .print = print });
 }
@@ -146,7 +146,7 @@ static bool printUnknownLocations = getEnv("_NIX_EVAL_SHOW_UNKNOWN_LOCATIONS").h
  *
  * @return true if a position was printed.
  */
-static bool printPosMaybe(std::ostream & oss, std::string_view indent, const std::shared_ptr<Pos> & pos) {
+static bool printPosMaybe(std::ostream & oss, std::string_view indent, const std::shared_ptr<const Pos> & pos) {
     bool hasPos = pos && *pos;
     if (hasPos) {
         oss << indent << ANSI_BLUE << "at " ANSI_WARNING << *pos << ANSI_NORMAL << ":";

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

@@ -78,7 +78,7 @@ enum struct TracePrint {
 };
 
 struct Trace {
-    std::shared_ptr<Pos> pos;
+    std::shared_ptr<const Pos> pos;
     HintFmt hint;
     TracePrint print = TracePrint::Default;
 };
@@ -88,7 +88,7 @@ inline std::strong_ordering operator<=>(const Trace& lhs, const Trace& rhs);
 struct ErrorInfo {
     Verbosity level;
     HintFmt msg;
-    std::shared_ptr<Pos> pos;
+    std::shared_ptr<const Pos> pos;
     std::list<Trace> traces;
     /**
      * Some messages are generated directly by expressions; notably `builtins.warn`, `abort`, `throw`.
@@ -172,7 +172,7 @@ public:
         err.status = status;
     }
 
-    void atPos(std::shared_ptr<Pos> pos) {
+    void atPos(std::shared_ptr<const Pos> pos) {
         err.pos = pos;
     }
 
@@ -182,12 +182,12 @@ public:
     }
 
     template<typename... Args>
-    void addTrace(std::shared_ptr<Pos> && e, std::string_view fs, const Args & ... args)
+    void addTrace(std::shared_ptr<const Pos> && e, std::string_view fs, const Args & ... args)
     {
         addTrace(std::move(e), HintFmt(std::string(fs), args...));
     }
 
-    void addTrace(std::shared_ptr<Pos> && e, HintFmt hint, TracePrint print = TracePrint::Default);
+    void addTrace(std::shared_ptr<const Pos> && e, HintFmt hint, TracePrint print = TracePrint::Default);
 
     bool hasTrace() const { return !err.traces.empty(); }
 

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

@@ -43,15 +43,10 @@ struct Pos
     Pos() { }
     Pos(uint32_t line, uint32_t column, Origin origin)
         : line(line), column(column), origin(origin) { }
-    Pos(Pos & other) = default;
-    Pos(const Pos & other) = default;
-    Pos(Pos && other) = default;
-    Pos(const Pos * other);
 
     explicit operator bool() const { return line > 0; }
 
-    /* TODO: Why std::shared_ptr<Pos> and not std::shared_ptr<const Pos>? */
+    operator std::shared_ptr<const Pos>() const;
-    operator std::shared_ptr<Pos>() const;
 
     /**
      * Return the contents of the source file.

src/libutil/logging.cc

@@ -166,7 +166,7 @@ Activity::Activity(Logger & logger, Verbosity lvl, ActivityType type,
     logger.startActivity(id, lvl, type, s, fields, parent);
 }
 
-void to_json(nlohmann::json & json, std::shared_ptr<Pos> pos)
+void to_json(nlohmann::json & json, std::shared_ptr<const Pos> pos)
 {
     if (pos) {
         json["line"] = pos->line;

src/libutil/position.cc

@@ -2,19 +2,9 @@
 
 namespace nix {
 
-Pos::Pos(const Pos * other)
+Pos::operator std::shared_ptr<const Pos>() const
 {
-    if (!other) {
+    return std::make_shared<const Pos>(*this);
-        return;
-    }
-    line = other->line;
-    column = other->column;
-    origin = other->origin;
-}
-
-Pos::operator std::shared_ptr<Pos>() const
-{
-    return std::make_shared<Pos>(&*this);
 }
 
 std::optional<LinesOfCode> Pos::getCodeLines() const