Refactor: Allow generators to decide default configuration for build

And allow them to read any cache values they need.

Source/cmGlobalGenerator.cxx

@@ -1878,6 +1878,10 @@ int cmGlobalGenerator::Build(
     output += "\n";
     return 1;
   }
+  std::string realConfig = config;
+  if (realConfig.empty()) {
+    realConfig = this->GetDefaultBuildConfig();
+  }
 
   int retVal = 0;
   cmSystemTools::SetRunCommandHideConsole(true);
@@ -1886,7 +1890,7 @@ int cmGlobalGenerator::Build(
 
   std::vector<GeneratedMakeCommand> makeCommand =
     this->GenerateBuildCommand(makeCommandCSTR, projectName, bindir, targets,
-                               config, fast, jobs, verbose, nativeOptions);
+                               realConfig, fast, jobs, verbose, nativeOptions);
 
   // Workaround to convince some commands to produce output.
   if (outputflag == cmSystemTools::OUTPUT_PASSTHROUGH &&
@@ -1898,7 +1902,7 @@ int cmGlobalGenerator::Build(
   if (clean) {
     std::vector<GeneratedMakeCommand> cleanCommand =
       this->GenerateBuildCommand(makeCommandCSTR, projectName, bindir,
-                                 { "clean" }, config, fast, jobs, verbose);
+                                 { "clean" }, realConfig, fast, jobs, verbose);
     output += "\nRun Clean Command:";
     output += cleanCommand.front().Printable();
     output += "\n";

Source/cmGlobalGenerator.h

@@ -44,6 +44,7 @@ class cmLocalGenerator;
 class cmMakefile;
 class cmOutputConverter;
 class cmSourceFile;
+class cmState;
 class cmStateDirectory;
 class cmake;
 
@@ -135,6 +136,12 @@ public:
   virtual bool SetGeneratorToolset(std::string const& ts, bool build,
                                    cmMakefile* mf);
 
+  /** Read any other cache entries needed for cmake --build. */
+  virtual bool ReadCacheEntriesForBuild(const cmState& /*state*/)
+  {
+    return true;
+  }
+
   /**
    * Create LocalGenerators and process the CMakeLists files. This does not
    * actually produce any makefiles, DSPs, etc.
@@ -382,6 +389,9 @@ public:
   // Lookup edit_cache target command preferred by this generator.
   virtual std::string GetEditCacheCommand() const { return ""; }
 
+  // Default config to use for cmake --build
+  virtual std::string GetDefaultBuildConfig() const { return "Debug"; }
+
   // Class to track a set of dependencies.
   using TargetDependSet = cmTargetDependSet;
 

Source/cmake.cxx

@@ -2767,6 +2767,10 @@ int cmake::Build(int jobs, const std::string& dir,
   }
 #endif
 
+  if (!this->GlobalGenerator->ReadCacheEntriesForBuild(*this->State)) {
+    return 1;
+  }
+
   this->GlobalGenerator->PrintBuildCommandAdvice(std::cerr, jobs);
   return this->GlobalGenerator->Build(
     jobs, "", dir, projName, targets, output, "", config, clean, false,

Source/cmakemain.cxx

@@ -350,7 +350,7 @@ int do_build(int ac, char const* const* av)
 #else
   int jobs = cmake::NO_BUILD_PARALLEL_LEVEL;
   std::vector<std::string> targets;
-  std::string config = "Debug";
+  std::string config;
   std::string dir;
   std::vector<std::string> nativeOptions;
   bool cleanFirst = false;