Fix missing headers, compile in C++20 mode, fix std::span usage

Author: TartanLlama

Cargo.lock

@@ -12,7 +12,7 @@
 #include <string.h> // memcpy
 #include <stdlib.h> // free
 #include <new>
-
+#include <span>
 
 namespace wit {
 /// @brief Helper class to map between IDs and resources
@@ -45,12 +45,6 @@ template <class R> class ResourceTable {
 /// @brief Replaces void in the error position of a result
 struct Void {};
 
-template<class To, class From>
-constexpr To bit_cast(const From& from) noexcept {
-  union Bits { From from; To to; };
-  Bits b; b.from = from; return b.to;
-}
-
 /// A string in linear memory, freed unconditionally using free
 ///
 /// A normal C++ string makes no guarantees about where the characters

crates/cpp/helper-types/wit.h

@@ -80,6 +80,7 @@ struct Includes {
     needs_tuple: bool,
     needs_assert: bool,
     needs_bit: bool,
+    needs_span: bool,
     // needs wit types
     needs_wit: bool,
     needs_memory: bool,
@@ -692,7 +693,7 @@ impl WorldGenerator for Cpp {
         if self.dependencies.needs_wit {
             files.push(
                 &format!("wit-guest.h"),
-                include_bytes!("../helper-types/wit-guest.h"),
+                include_bytes!("../helper-types/wit.h"),
             );
         }
         Ok(())
@@ -1498,13 +1499,13 @@ impl CppInterfaceGenerator<'_> {
                     let inner = self.type_name(ty, from_namespace, flavor);
                     match flavor {
                         Flavor::BorrowedArgument => {
-                            self.gen.dependencies.needs_wit = true;
+                            self.gen.dependencies.needs_span = true;
                             format!("std::span<{inner} const>")
                         }
                         Flavor::Argument(var)
                             if matches!(var, AbiVariant::GuestImport) || self.gen.opts.new_api =>
                         {
-                            self.gen.dependencies.needs_wit = true;
+                            self.gen.dependencies.needs_span = true;
                             format!("std::span<{inner} const>")
                         }
                         Flavor::Argument(AbiVariant::GuestExport) => {

crates/cpp/src/lib.rs

@@ -131,7 +131,7 @@ impl LanguageMethods for Cpp17 {
         .arg("-Wextra")
         .arg("-Werror")
         .arg("-Wno-unused-parameter")
-        .arg("-std=c++17")
+        .arg("-std=c++20")
         .arg("-c")
         .arg("-g")
         .arg("-o")
@@ -159,7 +159,7 @@ impl LanguageMethods for Cpp17 {
             .arg("-Werror")
             .arg("-Wc++-compat")
             .arg("-Wno-unused-parameter")
-            .arg("-std=c++17")
+            .arg("-std=c++20")
             .arg("-g")
             .arg("-o")
             .arg(&compile.output);

crates/test/src/cpp.rs

@@ -35,10 +35,10 @@ static bool equal(std::span<const R> const&a, std::vector<R> const& b) {
 }
 template<class R>
 static bool equal(wit::vector<R> const&a, std::vector<R> const& b) {
-    return equal(a.get_view(), std::span<R>(b));
+    return equal(a.get_view(), std::span<R const>(b));
 }
 static bool equal(wit::vector<wit::string> const&a, std::vector<std::string_view> const& b) {
-    return equal(a.get_view(), std::span<std::string_view>(b));
+    return equal(a.get_view(), std::span<std::string_view const>(b));
 }
 template<class R,class S, class T, class U>
 static bool equal(std::tuple<R,S> const&a, std::tuple<T,U> const& b) {

tests/runtime/lists/runner.cpp

@@ -29,7 +29,7 @@ static bool equal(std::span<const R> const&a, wit::vector<R> const& b) {
 }
 template<class R>
 static bool equal(std::span<const R> const&a, std::vector<R> const& b) {
-    return equal(a, std::span<R>(b));
+    return equal(a, std::span<const R>(b));
 }
 template<class R>
 static bool equal(wit::vector<R> const&a, std::vector<R> const& b) {
@@ -87,15 +87,15 @@ void exports::test::lists::to_test::ListParamLarge(std::span<std::string_view co
 }
 
 wit::vector<uint8_t> exports::test::lists::to_test::ListResult() {
-    return wit::vector<uint8_t>::from_view(std::span<uint8_t>(std::vector<uint8_t>{1, 2, 3, 4, 5}));
+    return wit::vector<uint8_t>::from_view(std::span<uint8_t const>(std::vector<uint8_t>{1, 2, 3, 4, 5}));
 }
 
 wit::string exports::test::lists::to_test::ListResult2() {
     return wit::string::from_view("hello!");
 }
 
 wit::vector<wit::string> exports::test::lists::to_test::ListResult3() {
-    return wit::vector<wit::string>::from_view(std::span<wit::string>(std::vector<wit::string>{wit::string::from_view("hello,"), wit::string::from_view("world!")}));
+    return wit::vector<wit::string>::from_view(std::span<wit::string const>(std::vector<wit::string>{wit::string::from_view("hello,"), wit::string::from_view("world!")}));
 }
 
 wit::vector<uint8_t> exports::test::lists::to_test::ListRoundtrip(std::span<const uint8_t> x) {