format: add 'quoted' helper function that emulates std::quoted

CMakeLists.txt

@@ -352,6 +352,7 @@ list (
     fixed_string.hpp
     float.cpp
     float.hpp
+    format/quoted.hpp
     fourcc.cpp
     fourcc.hpp
     fs/scoped.cpp
@@ -730,6 +731,7 @@ if (TESTS)
         extent
         fixed
         float
+        format/quoted
         fs/scoped
         fs/tmp
         geom/aabb

format/quoted.hpp

@@ -0,0 +1,85 @@
+#pragma once
+
+#include <fmt/format.h>
+
+namespace cruft::format {
+    namespace detail {
+        /// A utility string container that is rendered enclosed in quotes when formatted.
+        template <typename string_type = std::string_view>
+        struct escaped_string {
+            /// The string that needs to be escaped
+            string_type source;
+            /// The character marking the beginning and end of the string that needs to be escaped
+            typename string_type::value_type delim;
+            /// The character that escapes other characters
+            typename string_type::value_type escape;
+
+            constexpr bool
+            escaped_character (char c) const
+            {
+                return delim == c or escape == c;
+            }
+
+
+            /// Copies the string characters to an output iterator, inserting
+            /// delim and escape characters as required.
+            template <typename OutputT>
+            constexpr
+            OutputT
+            copy (OutputT dst) const
+            {
+                *dst++ = delim;
+
+                for (const auto& c : source) {
+                    if (escaped_character (c))
+                        *dst++ = escape;
+
+                    *dst++ = c;
+                }
+
+                *dst++ = delim;
+                return dst;
+            }
+        };
+    }
+
+    /// Returns an object that will be enclosed between delimiters. All
+    /// occurrences of this delimiter will be escaped with the supplied
+    /// character (as will occurences of this escape character).
+    constexpr
+    auto
+    quoted (
+        std::string_view source,
+        char delim = '"',
+        char escape = '\\'
+    ) {
+        return cruft::format::detail::escaped_string<
+            std::string_view
+        > {
+            .source = source,
+            .delim = delim,
+            .escape = escape,
+        };
+    }
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+template <typename string_type>
+struct fmt::formatter<cruft::format::detail::escaped_string<string_type>> {
+    constexpr
+    format_parse_context::iterator
+    parse (fmt::format_parse_context ctx) const
+    {
+        return ctx.begin();
+    }
+
+    constexpr
+    format_context::iterator
+    format(
+        cruft::format::detail::escaped_string<string_type> const& val,
+        format_context & ctx
+    ) const {
+        return val.copy (ctx.out());
+    }
+};

test/format/quoted.cpp

@@ -0,0 +1,32 @@
+#include <cruft/util/format/quoted.hpp>
+
+#include <cruft/util/tap.hpp>
+
+
+int main ()
+{
+    static constexpr struct {
+        std::string_view format;
+        std::string_view inner;
+        std::string_view result;
+        std::string_view message;
+    } TESTS[] = {
+        { "{}", "Foo", R"("Foo")", "Simple word" },
+        { "{}", "F\"oo", R"("F\"oo")", "Embedded delim" },
+        { "{}", "F\\oo", R"("F\\oo")", "Embedded escape" },
+    };
+
+    cruft::TAP::logger tap;
+
+    for (auto const &t: TESTS) {
+        auto const result = fmt::vformat (
+            t.format,
+            fmt::make_format_args (
+                cruft::format::quoted (t.inner)
+            )
+        );
+        tap.expect_eq (result, t.result, "quoted format: {}", t.message);
+    }
+
+    return tap.status ();
+}