Makefile: Fix multiple custom command outputs regression (#15116)

In commit v3.2.0-rc1~272^2~2 (Makefile: Fix rebuild with multiple custom
command outputs, 2014-12-05) we changed the generated makefile pattern
for multiple outputs from

  out1: depends...
          commands...
  out2: out1

to

  out1 out2: depends...
          commands...

This was based on the incorrect assumption that make tools would treat
this as a combined output rule and run the command(s) exactly once for
them.  It turns out that instead this new pattern is equivalent to

  out1: depends...
          commands...
  out2: depends...
          commands...

so the commands may be run more than once.

Some documents suggest using a "dedicated witness" stamp file:

  stamp: depends...
          rm -f stamp
          touch stamp.tmp
          commands...
          mv stamp.tmp stamp
  out1 out2: stamp

However, if the commands fail the error message will refer to the stamp
instead of any of the real outputs, which may be confusing to readers.
Also, this approach seems to have the same behavior of the original
approach that motiviated the above commit: multiple invocations are
needed to bring consumers of the outputs up to date.

Instead we can return to the original approach but add an explicit
touch to each extra output rule:

  out1: depends...
          commands...
  out2: out1
          touch -c out2

This causes make tools to recognize that all outputs have changed and
therefore to execute any commands that consume them.

1 files changed, 2 insertions, 54 deletions

diff --git a/Source/cmLocalUnixMakefileGenerator3.cxx b/Source/cmLocalUnixMakefileGenerator3.cxx
index dfa6cc9..9213ad6 100644
--- a/Source/cmLocalUnixMakefileGenerator3.cxx
+++ b/Source/cmLocalUnixMakefileGenerator3.cxx
@@ -92,7 +92,6 @@ cmLocalUnixMakefileGenerator3::cmLocalUnixMakefileGenerator3()
   this->SkipAssemblySourceRules = false;
   this->MakeCommandEscapeTargetTwice = false;
   this->BorlandMakeCurlyHack = false;
-  this->NoMultiOutputMultiDepRules = false;
 }
 
 //----------------------------------------------------------------------------
@@ -600,7 +599,6 @@ const std::string &cmLocalUnixMakefileGenerator3::GetHomeRelativeOutputPath()
   return this->HomeRelativeOutputPath;
 }
 
-
 //----------------------------------------------------------------------------
 void
 cmLocalUnixMakefileGenerator3
@@ -619,30 +617,6 @@ cmLocalUnixMakefileGenerator3
                          comment);
     return;
     }
-  std::vector<std::string> outputs(1, target);
-  this->WriteMakeRule(os, comment,
-                      outputs, depends, commands,
-                      symbolic, in_help);
-}
-
-//----------------------------------------------------------------------------
-void
-cmLocalUnixMakefileGenerator3
-::WriteMakeRule(std::ostream& os,
-                const char* comment,
-                const std::vector<std::string>& outputs,
-                const std::vector<std::string>& depends,
-                const std::vector<std::string>& commands,
-                bool symbolic,
-                bool in_help)
-{
-  // Make sure there is an output.
-  if(outputs.empty())
-    {
-    cmSystemTools::Error("No outputs for WriteMakeRule! called with comment: ",
-                         comment);
-    return;
-    }
 
   std::string replace;
 
@@ -661,17 +635,7 @@ cmLocalUnixMakefileGenerator3
     }
 
   // Construct the left hand side of the rule.
-  std::string tgt;
-  {
-  const char* sep = "";
-  for (std::vector<std::string>::const_iterator i = outputs.begin();
-       i != outputs.end(); ++i)
-    {
-    tgt += sep;
-    tgt += this->Convert(*i,HOME_OUTPUT,MAKERULE);
-    sep = " ";
-    }
-  }
+  std::string tgt = this->Convert(target, HOME_OUTPUT, MAKERULE);
 
   const char* space = "";
   if(tgt.size() == 1)
@@ -697,19 +661,6 @@ cmLocalUnixMakefileGenerator3
     // No dependencies.  The commands will always run.
     os << cmMakeSafe(tgt) << space << ":\n";
     }
-  else if(this->NoMultiOutputMultiDepRules && outputs.size() >= 2)
-    {
-    // Borland make does not understand multiple dependency rules when
-    // there are multiple outputs, so write them all on one line.
-    os << cmMakeSafe(tgt) << space << ":";
-    for(std::vector<std::string>::const_iterator dep = depends.begin();
-        dep != depends.end(); ++dep)
-      {
-      replace = this->Convert(*dep, HOME_OUTPUT, MAKERULE);
-      os << " " << cmMakeSafe(replace);
-      }
-    os << "\n";
-    }
   else
     {
     // Split dependencies into multiple rule lines.  This allows for
@@ -738,8 +689,7 @@ cmLocalUnixMakefileGenerator3
   // Add the output to the local help if requested.
   if(in_help)
     {
-    this->LocalHelp.insert(this->LocalHelp.end(),
-                           outputs.begin(), outputs.end());
+    this->LocalHelp.push_back(target);
     }
 }
 
@@ -1758,8 +1708,6 @@ cmLocalUnixMakefileGenerator3
 //----------------------------------------------------------------------------
 void cmLocalUnixMakefileGenerator3::CheckMultipleOutputs(bool verbose)
 {
-  // Nothing populates multiple output pairs anymore, but we need to
-  // honor it when working in a build tree generated by an older CMake.
   cmMakefile* mf = this->Makefile;
 
   // Get the string listing the multiple output pairs.