Defer check for sources within a target until generation.

The `add_library` and `add_executable` commands can now be called with
no source-files and won't generate a warning or error message, as long
as source-files will be added later via the `target_sources` command.
If during the generation step still no sources are associated with
targets created by such calls a useful error message will be generated
and generation fails.

Targets of type `INTERFACE_LIBRARY`, `UTILITY` or `GLOBAL_TARGET` are
excluded from this check because we do not need sources for these target
types during generation.

Fixes: #16872

4 files changed, 45 insertions, 15 deletions

diff --git a/Source/cmAddExecutableCommand.cxx b/Source/cmAddExecutableCommand.cxx
index 1d0376f..262e3a1 100644
--- a/Source/cmAddExecutableCommand.cxx
+++ b/Source/cmAddExecutableCommand.cxx
@@ -18,7 +18,7 @@ class cmExecutionStatus;
 bool cmAddExecutableCommand::InitialPass(std::vector<std::string> const& args,
                                          cmExecutionStatus&)
 {
-  if (args.size() < 2) {
+  if (args.empty()) {
     this->SetError("called with incorrect number of arguments");
     return false;
   }
@@ -191,12 +191,6 @@ bool cmAddExecutableCommand::InitialPass(std::vector<std::string> const& args,
     }
   }
 
-  if (s == args.end()) {
-    this->SetError(
-      "called with incorrect number of arguments, no sources provided");
-    return false;
-  }
-
   std::vector<std::string> srclists(s, args.end());
   cmTarget* tgt =
     this->Makefile->AddExecutable(exename.c_str(), srclists, excludeFromAll);
diff --git a/Source/cmAddLibraryCommand.cxx b/Source/cmAddLibraryCommand.cxx
index ebf1763..31c2ecf 100644
--- a/Source/cmAddLibraryCommand.cxx
+++ b/Source/cmAddLibraryCommand.cxx
@@ -362,14 +362,6 @@ bool cmAddLibraryCommand::InitialPass(std::vector<std::string> const& args,
     return true;
   }
 
-  if (s == args.end()) {
-    std::string msg = "You have called ADD_LIBRARY for library ";
-    msg += args[0];
-    msg += " without any source files. This typically indicates a problem ";
-    msg += "with your CMakeLists.txt file";
-    cmSystemTools::Message(msg.c_str(), "Warning");
-  }
-
   srclists.insert(srclists.end(), s, args.end());
 
   this->Makefile->AddLibrary(libName, type, srclists, excludeFromAll);
diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index 38669c9..000309f 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -261,6 +261,43 @@ void cmGlobalGenerator::ForceLinkerLanguages()
 {
 }
 
+bool cmGlobalGenerator::CheckTargetsForMissingSources() const
+{
+  bool failed = false;
+  for (cmLocalGenerator* localGen : this->LocalGenerators) {
+    const std::vector<cmGeneratorTarget*>& targets =
+      localGen->GetGeneratorTargets();
+
+    for (cmGeneratorTarget* target : targets) {
+      if (target->GetType() == cmStateEnums::TargetType::GLOBAL_TARGET ||
+          target->GetType() == cmStateEnums::TargetType::INTERFACE_LIBRARY ||
+          target->GetType() == cmStateEnums::TargetType::UTILITY) {
+        continue;
+      }
+
+      std::vector<std::string> configs;
+      target->Makefile->GetConfigurations(configs);
+      std::vector<cmSourceFile*> srcs;
+      if (configs.empty()) {
+        target->GetSourceFiles(srcs, "");
+      } else {
+        for (std::vector<std::string>::const_iterator ci = configs.begin();
+             ci != configs.end() && srcs.empty(); ++ci) {
+          target->GetSourceFiles(srcs, *ci);
+        }
+      }
+      if (srcs.empty()) {
+        std::ostringstream e;
+        e << "No SOURCES given to target: " << target->GetName();
+        this->GetCMakeInstance()->IssueMessage(cmake::FATAL_ERROR, e.str(),
+                                               target->GetBacktrace());
+        failed = true;
+      }
+    }
+  }
+  return failed;
+}
+
 bool cmGlobalGenerator::IsExportedTargetsFile(
   const std::string& filename) const
 {
@@ -1292,6 +1329,11 @@ bool cmGlobalGenerator::Compute()
     localGen->TraceDependencies();
   }
 
+  // Make sure that all (non-imported) targets have source files added!
+  if (this->CheckTargetsForMissingSources()) {
+    return false;
+  }
+
   this->ForceLinkerLanguages();
 
   // Compute the manifest of main targets generated.
diff --git a/Source/cmGlobalGenerator.h b/Source/cmGlobalGenerator.h
index 04e9dc1..1f90ecf 100644
--- a/Source/cmGlobalGenerator.h
+++ b/Source/cmGlobalGenerator.h
@@ -539,6 +539,8 @@ private:
 
   virtual void ForceLinkerLanguages();
 
+  bool CheckTargetsForMissingSources() const;
+
   void CreateLocalGenerators();
 
   void CheckCompilerIdCompatibility(cmMakefile* mf,