add Expr::kind() -> string method, purely for debugging

src/libexpr/nixexpr.cc

@@ -581,6 +581,146 @@ std::string ExprLambda::showNamePos(const EvalState & state) const
 }
 
 
+std::string_view Expr::kind() const
+{
+    return "abstract";
+}
+
+std::string_view ExprInt::kind() const
+{
+    return "int";
+}
+
+std::string_view ExprFloat::kind() const
+{
+    return "float";
+}
+
+std::string_view ExprString::kind() const
+{
+    return "string";
+}
+
+std::string_view ExprPath::kind() const
+{
+    return "path";
+}
+
+std::string_view ExprVar::kind() const
+{
+    return "var";
+}
+
+std::string_view ExprInheritFrom::kind() const
+{
+    return "inherit from";
+}
+
+std::string_view ExprSelect::kind() const
+{
+    return "select";
+}
+
+std::string_view ExprOpHasAttr::kind() const
+{
+    return "hasattr operator";
+}
+
+std::string_view ExprAttrs::kind() const
+{
+    return "attrs";
+}
+
+std::string_view ExprList::kind() const
+{
+    return "list";
+}
+
+std::string_view ExprLambda::kind() const
+{
+    return "lambda";
+}
+
+std::string_view ExprCall::kind() const
+{
+    return "call";
+}
+
+std::string_view ExprLet::kind() const
+{
+    return "let";
+}
+
+std::string_view ExprWith::kind() const
+{
+    return "with";
+}
+
+std::string_view ExprIf::kind() const
+{
+    return "if";
+}
+
+std::string_view ExprAssert::kind() const
+{
+    return "assert";
+}
+
+std::string_view ExprOpNot::kind() const
+{
+    return "not operator";
+}
+
+std::string_view ExprOpEq::kind() const
+{
+    return "equality operator";
+}
+
+std::string_view ExprOpNEq::kind() const
+{
+    return "inequality operator";
+}
+
+std::string_view ExprOpAnd::kind() const
+{
+    return "logical AND operator";
+}
+
+std::string_view ExprOpOr::kind() const
+{
+    return "logical OR operator";
+}
+
+std::string_view ExprOpImpl::kind() const
+{
+    return "logical implication operator";
+}
+
+std::string_view ExprOpUpdate::kind() const
+{
+    return "update operator";
+}
+
+std::string_view ExprOpConcatLists::kind() const
+{
+    return "list concatenation operator";
+}
+
+std::string_view ExprConcatStrings::kind() const
+{
+    return "string concatenation";
+}
+
+std::string_view ExprPos::kind() const
+{
+    return "position";
+}
+
+std::string_view ExprBlackHole::kind() const
+{
+    return "blackhole";
+}
+
 
 /* Position table. */
 

src/libexpr/nixexpr.hh

@@ -63,12 +63,15 @@ public:
     virtual Value * maybeThunk(EvalState & state, Env & env);
     virtual void setName(Symbol name);
     virtual PosIdx getPos() const { return noPos; }
+    /** Entirely for debugging. */
+    virtual std::string_view kind() const;
 };
 
 #define COMMON_METHODS \
     void show(const SymbolTable & symbols, std::ostream & str) const override; \
     void eval(EvalState & state, Env & env, Value & v) override; \
-    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override; \
+    virtual std::string_view kind() const override;
 
 struct ExprInt : Expr
 {
@@ -151,7 +154,8 @@ struct ExprInheritFrom : ExprVar
         this->fromWith = nullptr;
     }
 
-    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env);
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
+    std::string_view kind() const override;
 };
 
 struct ExprSelect : Expr
@@ -418,6 +422,7 @@ struct ExprOpNot : Expr
         } \
         void eval(EvalState & state, Env & env, Value & v) override; \
         PosIdx getPos() const override { return pos; } \
+        std::string_view kind() const override; \
     };
 
 MakeBinOp(ExprOpEq, "==")
@@ -453,6 +458,7 @@ struct ExprBlackHole : Expr
     void show(const SymbolTable & symbols, std::ostream & str) const override {}
     void eval(EvalState & state, Env & env, Value & v) override;
     void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override {}
+    std::string_view kind() const override;
 };
 
 extern ExprBlackHole eBlackHole;