cmake: Add options for parallel builds to --build mode

While we already support `cmake --build . -- -j`, the options after `--`
are specific to the native build tool.  Add new options `--parallel
[<N>]` and `-j [<N>]` to abstract this and map to the proper option
for the native build tool.

1 files changed, 49 insertions, 1 deletions

diff --git a/Source/cmakemain.cxx b/Source/cmakemain.cxx
index b185a1b..9c9f65c 100644
--- a/Source/cmakemain.cxx
+++ b/Source/cmakemain.cxx
@@ -22,6 +22,8 @@
 #if defined(_WIN32) && defined(CMAKE_BUILD_WITH_CMAKE)
 #include "cmsys/ConsoleBuf.hxx"
 #endif
+
+#include <ctype.h>
 #include <iostream>
 #include <string.h>
 #include <string>
@@ -49,6 +51,12 @@ static const char* cmDocumentationUsageNote[][2] = {
 
 #define CMAKE_BUILD_OPTIONS                                                   \
   "  <dir>          = Project binary directory to be built.\n"                \
+  "  -j [<jobs>] --parallel [<jobs>] = Build in parallel using\n"             \
+  "                   the given number of jobs. If <jobs> is omitted\n"       \
+  "                   the native build tool's default number is used.\n"      \
+  "                   The CMAKE_BUILD_PARALLEL_LEVEL environment variable\n"  \
+  "                   specifies a default parallel level when this option\n"  \
+  "                   is not given.\n"                                        \
   "  --target <tgt> = Build <tgt> instead of default targets.\n"              \
   "                   May only be specified once.\n"                          \
   "  --config <cfg> = For multi-configuration tools, choose <cfg>.\n"         \
@@ -338,6 +346,7 @@ static int do_build(int ac, char const* const* av)
   std::cerr << "This cmake does not support --build\n";
   return -1;
 #else
+  int jobs = cmake::NO_BUILD_PARALLEL_LEVEL;
   std::string target;
   std::string config = "Debug";
   std::string dir;
@@ -348,6 +357,7 @@ static int do_build(int ac, char const* const* av)
   enum Doing
   {
     DoingNone,
+    DoingJobs,
     DoingDir,
     DoingTarget,
     DoingConfig,
@@ -357,6 +367,13 @@ static int do_build(int ac, char const* const* av)
   for (int i = 2; i < ac; ++i) {
     if (doing == DoingNative) {
       nativeOptions.push_back(av[i]);
+    } else if ((strcmp(av[i], "-j") == 0) ||
+               (strcmp(av[i], "--parallel") == 0)) {
+      jobs = cmake::DEFAULT_BUILD_PARALLEL_LEVEL;
+      /* does the next argument start with a number? */
+      if ((i + 1 < ac) && (isdigit(*av[i + 1]))) {
+        doing = DoingJobs;
+      }
     } else if (strcmp(av[i], "--target") == 0) {
       if (!hasTarget) {
         doing = DoingTarget;
@@ -377,6 +394,18 @@ static int do_build(int ac, char const* const* av)
       doing = DoingNative;
     } else {
       switch (doing) {
+        case DoingJobs: {
+          unsigned long numJobs = 0;
+          if (cmSystemTools::StringToULong(av[i], &numJobs)) {
+            jobs = int(numJobs);
+            doing = DoingNone;
+          } else {
+            std::cerr << "'" << av[i - 1] << "' invalid number '" << av[i]
+                      << "' given.\n\n";
+            dir.clear();
+            break;
+          }
+        } break;
         case DoingDir:
           dir = cmSystemTools::CollapseFullPath(av[i]);
           doing = DoingNone;
@@ -396,6 +425,25 @@ static int do_build(int ac, char const* const* av)
       }
     }
   }
+
+  if (jobs == cmake::NO_BUILD_PARALLEL_LEVEL) {
+    std::string parallel;
+    if (cmSystemTools::GetEnv("CMAKE_BUILD_PARALLEL_LEVEL", parallel)) {
+      if (parallel.empty()) {
+        jobs = cmake::DEFAULT_BUILD_PARALLEL_LEVEL;
+      } else {
+        unsigned long numJobs = 0;
+        if (cmSystemTools::StringToULong(parallel.c_str(), &numJobs)) {
+          jobs = int(numJobs);
+        } else {
+          std::cerr << "'CMAKE_BUILD_PARALLEL_LEVEL' environment variable\n"
+                    << "invalid number '" << parallel << "' given.\n\n";
+          dir.clear();
+        }
+      }
+    }
+  }
+
   if (dir.empty()) {
     /* clang-format off */
     std::cerr <<
@@ -410,7 +458,7 @@ static int do_build(int ac, char const* const* av)
   cmake cm(cmake::RoleInternal);
   cmSystemTools::SetMessageCallback(cmakemainMessageCallback, &cm);
   cm.SetProgressCallback(cmakemainProgressCallback, &cm);
-  return cm.Build(dir, target, config, nativeOptions, clean);
+  return cm.Build(jobs, dir, target, config, nativeOptions, clean);
 #endif
 }