VS: Do not concurrently build custom commands with generated MAIN_DEPENDENCY

Since commit 33c15ae2b9 (VS: Build custom commands concurrently when
possible, 2023-01-19) several tests have failed intermittently with the
VS generator.  It seems that if the `BuildInParallel` setting is
attached to a generated input:

    <CustomBuild Include="generated_input.txt">
      <BuildInParallel Condition="...">true</BuildInParallel>
      <Command Condition="...">copy geneated_input.txt output.txt</Command>
      ...
    </CustomBuild>

then MSBuild does not wait for the input to be generated before running
the command.

This occurs when using `add_custom_command`'s `MAIN_DEPENDENCY`, so
avoid using `BuildInParallel` in that case.

Issue: #18405

2 files changed, 16 insertions, 6 deletions

diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 5065876..7b3f348 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx
@@ -1806,9 +1806,13 @@ void cmVisualStudio10TargetGenerator::WriteCustomRule(
       this->WriteCustomRuleCSharp(e0, c, name, script, additional_inputs.str(),
                                   outputs.str(), comment, ccg);
     } else {
-      this->WriteCustomRuleCpp(*spe2, c, script, additional_inputs.str(),
-                               outputs.str(), comment, ccg, symbolic,
-                               command.GetUsesTerminal());
+      this->WriteCustomRuleCpp(
+        *spe2, c, script, additional_inputs.str(), outputs.str(), comment, ccg,
+        symbolic,
+        (command.GetUsesTerminal() ||
+         (command.HasMainDependency() && source->GetIsGenerated()))
+          ? BuildInParallel::No
+          : BuildInParallel::Yes);
     }
   }
 }
@@ -1817,10 +1821,11 @@ void cmVisualStudio10TargetGenerator::WriteCustomRuleCpp(
   Elem& e2, std::string const& config, std::string const& script,
   std::string const& additional_inputs, std::string const& outputs,
   std::string const& comment, cmCustomCommandGenerator const& ccg,
-  bool symbolic, bool uses_terminal)
+  bool symbolic, BuildInParallel buildInParallel)
 {
   const std::string cond = this->CalcCondition(config);
-  if (this->GlobalGenerator->IsBuildInParallelSupported() && !uses_terminal) {
+  if (buildInParallel == BuildInParallel::Yes &&
+      this->GlobalGenerator->IsBuildInParallelSupported()) {
     e2.WritePlatformConfigTag("BuildInParallel", cond, "true");
   }
   e2.WritePlatformConfigTag("Message", cond, comment);
diff --git a/Source/cmVisualStudio10TargetGenerator.h b/Source/cmVisualStudio10TargetGenerator.h
index 194fbaa..e00f692 100644
--- a/Source/cmVisualStudio10TargetGenerator.h
+++ b/Source/cmVisualStudio10TargetGenerator.h
@@ -152,13 +152,18 @@ private:
   void OutputLinkIncremental(Elem& e1, std::string const& configName);
   void WriteCustomRule(Elem& e0, cmSourceFile const* source,
                        cmCustomCommand const& command);
+  enum class BuildInParallel
+  {
+    No,
+    Yes,
+  };
   void WriteCustomRuleCpp(Elem& e2, std::string const& config,
                           std::string const& script,
                           std::string const& additional_inputs,
                           std::string const& outputs,
                           std::string const& comment,
                           cmCustomCommandGenerator const& ccg, bool symbolic,
-                          bool uses_terminal);
+                          BuildInParallel buildInParallel);
   void WriteCustomRuleCSharp(Elem& e0, std::string const& config,
                              std::string const& commandName,
                              std::string const& script,