rename SymbolIdx -> Symbol, Symbol -> SymbolStr

after #6218 `Symbol` no longer confers a uniqueness invariant on the
string it wraps, it is now possible to create multiple symbols that
compare equal but whose string contents have different addresses. this
guarantee is now only provided by `SymbolIdx`, leaving `Symbol` only as
a string wrapper that knows about the intricacies of how symbols need to
be formatted for output.

this change renames `SymbolIdx` to `Symbol` to restore the previous
semantics of `Symbol` to that name. we also keep the wrapper type and
rename it to `SymbolStr` instead of returning plain strings from lookups
into the symbol table because symbols are formatted for output in many
places. theoretically we do not need `SymbolStr`, only a function that
formats a string for output as a symbol, but having to wrap every symbol
that appears in a message into eg `formatSymbol()` is error-prone and
inconvient.

1 files changed, 8 insertions, 11 deletions

diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 9fee3cb58..c529fdc89 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -24,8 +24,10 @@ static void showString(std::ostream & str, std::string_view s)
     str << '"';
 }
 
-static void showId(std::ostream & str, std::string_view s)
+std::ostream & operator <<(std::ostream & str, const SymbolStr & symbol)
 {
+    std::string_view s = symbol;
+
     if (s.empty())
         str << "\"\"";
     else if (s == "if") // FIXME: handle other keywords
@@ -34,7 +36,7 @@ static void showId(std::ostream & str, std::string_view s)
         char c = s[0];
         if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_')) {
             showString(str, s);
-            return;
+            return str;
         }
         for (auto c : s)
             if (!((c >= 'a' && c <= 'z') ||
@@ -42,15 +44,10 @@ static void showId(std::ostream & str, std::string_view s)
                   (c >= '0' && c <= '9') ||
                   c == '_' || c == '\'' || c == '-')) {
                 showString(str, s);
-                return;
+                return str;
             }
         str << s;
     }
-}
-
-std::ostream & operator << (std::ostream & str, const Symbol & sym)
-{
-    showId(str, sym.s);
     return str;
 }
 
@@ -499,12 +496,12 @@ void ExprPos::bindVars(const EvalState & es, const StaticEnv & env)
 
 /* Storing function names. */
 
-void Expr::setName(SymbolIdx name)
+void Expr::setName(Symbol name)
 {
 }
 
 
-void ExprLambda::setName(SymbolIdx name)
+void ExprLambda::setName(Symbol name)
 {
     this->name = name;
     body->setName(name);
@@ -526,7 +523,7 @@ std::string ExprLambda::showNamePos(const EvalState & state) const
 size_t SymbolTable::totalSize() const
 {
     size_t n = 0;
-    dump([&] (const Symbol & s) { n += std::string_view(s).size(); });
+    dump([&] (const std::string & s) { n += s.size(); });
     return n;
 }