add_custom_{command,target}: Fix WORKING_DIRECTORY leading genex

Since commit v3.13.0-rc1~39^2 (add_custom_{command,target}:
WORKING_DIRECTORY generator expressions, 2018-09-22) the
`WORKING_DIRECTORY` option accepts generator expressions.
Fix support for the case of a leading generator expression
by deferring conversion to an absolute path until after
evaluation of the generator expression.

Fixes: #18543

1 files changed, 6 insertions, 0 deletions

diff --git a/Source/cmCustomCommandGenerator.cxx b/Source/cmCustomCommandGenerator.cxx
index 5bbae17..d1c1736 100644
--- a/Source/cmCustomCommandGenerator.cxx
+++ b/Source/cmCustomCommandGenerator.cxx
@@ -70,6 +70,12 @@ cmCustomCommandGenerator::cmCustomCommandGenerator(cmCustomCommand const& cc,
     std::unique_ptr<cmCompiledGeneratorExpression> cge =
       this->GE->Parse(workingdirectory);
     this->WorkingDirectory = cge->Evaluate(this->LG, this->Config);
+    // Convert working directory to a full path.
+    if (!this->WorkingDirectory.empty()) {
+      std::string const& build_dir = this->LG->GetCurrentBinaryDirectory();
+      this->WorkingDirectory =
+        cmSystemTools::CollapseFullPath(this->WorkingDirectory, build_dir);
+    }
   }
 }