From 298bae0058fba5b1a26240a92ce632b73516553c Mon Sep 17 00:00:00 2001
From: Zach Laine <whatwasthataddress@gmail.com>
Date: Sat, 9 Nov 2024 22:29:40 -0600
Subject: [PATCH] Sketch in the printing implemetnation for token_parser.

See #202.
---
 include/boost/parser/detail/printing.hpp      |  7 ++++
 include/boost/parser/detail/printing_impl.hpp | 35 +++++++++++++++++++
 include/boost/parser/token_parser.hpp         |  1 -
 test/tracing.cpp                              | 11 ++++++
 4 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/include/boost/parser/detail/printing.hpp b/include/boost/parser/detail/printing.hpp
index 1143832a..7f6854c7 100644
--- a/include/boost/parser/detail/printing.hpp
+++ b/include/boost/parser/detail/printing.hpp
@@ -355,6 +355,13 @@ namespace boost { namespace parser { namespace detail {
         std::ostream & os,
         int components = 0);
 
+    template<typename Context, typename TokenSpec, typename Expected>
+    void print_parser(
+        Context const & context,
+        token_parser<TokenSpec, Expected> const & parser,
+        std::ostream & os,
+        int components = 0);
+
     enum { trace_indent_factor = 2 };
 
     inline void trace_indent(std::ostream & os, int indent)
diff --git a/include/boost/parser/detail/printing_impl.hpp b/include/boost/parser/detail/printing_impl.hpp
index 37f780c5..2493bb2a 100644
--- a/include/boost/parser/detail/printing_impl.hpp
+++ b/include/boost/parser/detail/printing_impl.hpp
@@ -942,6 +942,41 @@ namespace boost { namespace parser { namespace detail {
             context, parser.or_parser_, os, components);
     }
 
+#if defined(BOOST_PARSER_TOKEN_PARSER_HPP)
+
+    // TODO: Needs testing.
+    template<typename Context, typename TokenSpec, typename Expected>
+    void print_parser(
+        Context const & context,
+        token_parser<TokenSpec, Expected> const & parser,
+        std::ostream & os,
+        int components)
+    {
+        os << "tok<";
+        if constexpr (requires { os << TokenSpec::id; }) {
+            os << TokenSpec::id;
+        } else {
+            os << (int)TokenSpec::id;
+        }
+        os << '>';
+        if constexpr (requires { parser.expected_.value_; }) {
+            os << '(';
+            if constexpr (std::ranges::range<
+                              decltype(parser.expected_.value_)>) {
+                os << '"';
+                for (auto c : parser.expected_.value_ | text::as_utf8) {
+                    detail::print_char(os, c);
+                }
+                os << '"';
+            } else {
+                detail::print(os, parser.expected_.value_);
+            }
+            os << ')';
+        }
+    }
+
+#endif
+
 }}}
 
 #endif
diff --git a/include/boost/parser/token_parser.hpp b/include/boost/parser/token_parser.hpp
index 3d729813..06bc5cc9 100644
--- a/include/boost/parser/token_parser.hpp
+++ b/include/boost/parser/token_parser.hpp
@@ -69,7 +69,6 @@ namespace boost { namespace parser {
 
 #ifndef BOOST_PARSER_DOXYGEN
 
-    // TODO: Needs a printer.
     // TODO: Constrain the AttributeType to something that detail::token_as()
     // can handle.
     template<typename TokenSpec, typename Expected>
diff --git a/test/tracing.cpp b/test/tracing.cpp
index 1d94fb53..eb94b00a 100644
--- a/test/tracing.cpp
+++ b/test/tracing.cpp
@@ -26,6 +26,17 @@ struct globals_t
 
 globals_t const globals;
 
+enum class unprintable_tokens { foo, bar };
+enum class printable_tokens { foo, bar };
+std::ostream & operator<<(std::ostream & os, printable_tokens tok)
+{
+    switch (tok) {
+    case printable_tokens::foo: os << "foo"; break;
+    case printable_tokens::bar: os << "bar"; break;
+    }
+    return os;
+}
+
 auto i = [](auto & ctx) { return _globals(ctx).i; };
 auto i2 = [](auto & ctx) { return _globals(ctx).i2; };
 auto u = [](auto & ctx) { return _globals(ctx).u; };