file(DOWNLOAD|UPLOAD): Warn on unexpected arguments

Emit warning message on unparsed argument instead of silently ignoring it.
Can't stop with the error message because it may break old code.

Source/cmFileCommand.cxx

@@ -2564,6 +2564,11 @@ bool cmFileCommand::HandleDownloadCommand(std::vector<std::string> const& args)
         return false;
       }
       hashMatchMSG = algo + " hash";
+    } else {
+      // Do not return error for compatibility reason.
+      std::string err = "Unexpected argument: ";
+      err += *i;
+      this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, err.c_str());
     }
     ++i;
   }
@@ -2812,6 +2817,11 @@ bool cmFileCommand::HandleUploadCommand(std::vector<std::string> const& args)
       statusVar = *i;
     } else if (*i == "SHOW_PROGRESS") {
       showProgress = true;
+    } else {
+      // Do not return error for compatibility reason.
+      std::string err = "Unexpected argument: ";
+      err += *i;
+      this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, err.c_str());
     }
 
     ++i;

Tests/RunCMake/file/DOWNLOAD-unused-argument-stderr.txt

@@ -0,0 +1,5 @@
+^CMake Warning \(dev\) at DOWNLOAD-unused-argument.cmake:[0-9]+ \(file\):
+  Unexpected argument: JUNK
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
+This warning is for project developers.  Use -Wno-dev to suppress it.$

Tests/RunCMake/file/DOWNLOAD-unused-argument.cmake

@@ -0,0 +1,5 @@
+file(DOWNLOAD
+  "file://${CMAKE_CURRENT_SOURCE_DIR}/DOWNLOAD-unused-argument.txt"
+  "${CMAKE_CURRENT_BINARY_DIR}/unused-argument.txt"
+  JUNK
+  )

Tests/RunCMake/file/RunCMakeTest.cmake

@@ -1,6 +1,8 @@
 include(RunCMake)
 
 run_cmake(DOWNLOAD-hash-mismatch)
+run_cmake(DOWNLOAD-unused-argument)
+run_cmake(UPLOAD-unused-argument)
 run_cmake(INSTALL-DIRECTORY)
 run_cmake(INSTALL-MESSAGE-bad)
 run_cmake(FileOpenFailRead)

Tests/RunCMake/file/UPLOAD-unused-argument-stderr.txt

@@ -0,0 +1,5 @@
+^CMake Warning \(dev\) at UPLOAD-unused-argument.cmake:[0-9]+ \(file\):
+  Unexpected argument: JUNK
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
+This warning is for project developers.  Use -Wno-dev to suppress it.$

Tests/RunCMake/file/UPLOAD-unused-argument.cmake

@@ -0,0 +1,5 @@
+file(UPLOAD
+  "${CMAKE_CURRENT_SOURCE_DIR}/UPLOAD-unused-argument.txt"
+  "file://${CMAKE_CURRENT_BINARY_DIR}/unused-argument.txt"
+  JUNK
+  )