MSVC: Fix issues so cmake build works.

c++/src/capnp/CMakeLists.txt

@@ -188,7 +188,6 @@ if(BUILD_TESTING)
     blob-test.c++
     endian-test.c++
     endian-fallback-test.c++
-    endian-reverse-test.c++
     layout-test.c++
     any-test.c++
     message-test.c++
@@ -206,6 +205,7 @@ if(BUILD_TESTING)
 
   if(NOT CAPNP_LITE)
     add_executable(capnp-heavy-tests
+      endian-reverse-test.c++
       capability-test.c++
       schema-test.c++
       schema-loader-test.c++

c++/src/capnp/compiler/capnp.c++

@@ -335,11 +335,53 @@ public:
   kj::MainBuilder::Validity addOutput(kj::StringPtr spec) {
     KJ_IF_MAYBE(split, spec.findFirst(':')) {
       kj::StringPtr dir = spec.slice(*split + 1);
+      auto plugin = spec.slice(0, *split);
+
+      KJ_IF_MAYBE(split2, dir.findFirst(':')) {
+        // Grr, there are two colons. Might this be a Windows path? Let's do some heuristics.
+        if (*split == 1 && (dir.startsWith("/") || dir.startsWith("\\"))) {
+          // So, the first ':' was the second char, and was followed by '/' or '\', e.g.:
+          //     capnp compile -o c:/foo.exe:bar
+          //
+          // In this case we can conclude that the second colon is actually meant to be the
+          // plugin/location separator, and the first colon was simply signifying a drive letter.
+          //
+          // Proof by contradiction:
+          // - Say that none of the colons were meant to be plugin/location separators; i.e. the
+          //   whole argument is meant to be a plugin indicator and the location defaults to ".".
+          //   -> In this case, the plugin path has two colons, which is not valid.
+          //   -> CONTRADICTION
+          // - Say that the first colon was meant to be the plugin/location separator.
+          //   -> In this case, the second colon must be the drive letter separator for the
+          //      output location.
+          //   -> However, the output location begins with '/' or '\', which is not a drive letter.
+          //   -> CONTRADICTION
+          // - Say that there are more colons beyond the first two, and one of these is meant to
+          //   be the plugin/location separator.
+          //   -> In this case, the plugin path has two or more colons, which is not valid.
+          //   -> CONTRADICTION
+          //
+          // We therefore conclude that the *second* colon is in fact the plugin/location separator.
+          //
+          // Note that there is still an ambiguous case:
+          //     capnp compile -o c:/foo
+          //
+          // In this unfortunate case, we have no way to tell if the user meant "use the 'c' plugin
+          // and output to /foo" or "use the plugin c:/foo and output to the default location". We
+          // prefer the former interpretation, because the latter is Windows-specific and such
+          // users can always explicitly specify the output location like:
+          //     capnp compile -o c:/foo:.
+
+          dir = dir.slice(*split2 + 1);
+          plugin = spec.slice(0, *split2 + 2);
+        }
+      }
+
       struct stat stats;
       if (stat(dir.cStr(), &stats) < 0 || !S_ISDIR(stats.st_mode)) {
         return "output location is inaccessible or is not a directory";
       }
-      outputs.add(OutputDirective { spec.slice(0, *split), dir });
+      outputs.add(OutputDirective { plugin, dir });
     } else {
       outputs.add(OutputDirective { spec.asArray(), nullptr });
     }
@@ -405,7 +447,11 @@ public:
       kj::String exeName;
       bool shouldSearchPath = true;
       for (char c: output.name) {
+#if _WIN32
+        if (c == '/' || c == '\\') {
+#else
         if (c == '/') {
+#endif
           shouldSearchPath = false;
           break;
         }
@@ -445,18 +491,31 @@ public:
 
         if (shouldSearchPath) {
 #if _WIN32
-          child = _spawnlp(_P_NOWAIT, exeName.cStr(), exeName.cStr(), nullptr);
+          // MSVCRT's spawn*() don't correctly escape arguments, which is necessary on Windows
+          // since the underlying system call takes a single command line string rather than
+          // an arg list. Instead of trying to do the escaping ourselves, we just pass "plugin"
+          // for argv[0].
+          child = _spawnlp(_P_NOWAIT, exeName.cStr(), "plugin", nullptr);
 #else
           execlp(exeName.cStr(), exeName.cStr(), nullptr);
 #endif
         } else {
+#if _WIN32
+          if (!exeName.startsWith("/") && !exeName.startsWith("\\") &&
+              !(exeName.size() >= 2 && exeName[1] == ':')) {
+#else
           if (!exeName.startsWith("/")) {
+#endif
             // The name is relative.  Prefix it with our original working directory path.
             exeName = kj::str(pwd.begin(), "/", exeName);
           }
 
 #if _WIN32
-          child = _spawnl(_P_NOWAIT, exeName.cStr(), exeName.cStr(), nullptr);
+          // MSVCRT's spawn*() don't correctly escape arguments, which is necessary on Windows
+          // since the underlying system call takes a single command line string rather than
+          // an arg list. Instead of trying to do the escaping ourselves, we just pass "plugin"
+          // for argv[0].
+          child = _spawnl(_P_NOWAIT, exeName.cStr(), "plugin", nullptr);
 #else
           execl(exeName.cStr(), exeName.cStr(), nullptr);
 #endif

cmake/FindCapnProto.cmake

@@ -76,7 +76,7 @@ function(CAPNP_GENERATE_CPP SOURCES HEADERS)
     # Prepend a ':' to get the format for the '-o' flag right
     set(output_dir ":${CAPNPC_OUTPUT_DIR}")
   else()
-    set(output_dir)
+    set(output_dir ":.")
   endif()
 
   if(NOT DEFINED CAPNPC_SRC_PREFIX)