Why does MATLAB not recognize my Xcode 9 installation when running "mex -setup"?

Why does MATLAB report that I have "No supported compiler" when I execute "mex -setup", even though I have Xcode 9 installed on my machine and it is shown as a supported compiler on MathWorks.com?

 

 >> mex -setup -v
 Verbose mode is on.
 ... Looking for compiler 'Xcode with Clang' ...
 ... Looking for environment variable 'DEVELOPER_DIR' ...No.
 ... Executing command 'xcode-select -print-path' ...Yes ('/Library/Developer/CommandLineTools').
 ... Looking for folder '/Library/Developer/CommandLineTools' ...Yes.
 ... Executing command 'which xcrun' ...Yes ('/usr/bin/xcrun').
 ... Looking for folder '/usr/bin' ...Yes.
 ... Executing command 'defaults read com.apple.dt.Xcode IDEXcodeVersionForAgreedToGMLicense' ...No.
 ... Executing command 'defaults read /Library/Preferences/com.apple.dt.Xcode IDEXcodeVersionForAgreedToGMLicense' ...Yes ('9.0').
 ... Executing command '
 agreed=9.0 
  if echo $agreed | grep -E '[\.\"]' >/dev/null; then 
  lhs=`expr "$agreed" : '\([0-9]*\)[\.].*'` 
   rhs=`expr "$agreed" : '[0-9]*[\.]\(.*\)$'` 
  if echo $rhs | grep -E '[\."]' >/dev/null; then 
  rhs=`expr "$rhs" : '\([0-9]*\)[\.].*'` 
  fi 
  if [ $lhs -gt 4 ] || ( [ $lhs -eq 4 ] && [ $rhs -ge 3 ] ); then 
  echo $agreed 
  else 
  exit 1
  fi 
  fi' ...Yes ('9.0').
 ... Executing command 'xcrun -sdk macosx --show-sdk-path' ...No.
 Did not find installed compiler 'Xcode with Clang'.
 Error using mex
 No supported compiler or SDK was found. For options, visit
 <https://www.mathworks.com/support/compilers>.

 

Answer 1

[MathWorks Support Team]

"xcode-select -print-path" is reporting that the active developer directory is currently "/Library/Developer/CommandLineTools":

... Executing command 'xcode-select -print-path' ...Yes ('/Library/Developer/CommandLineTools').

This should be changed to the location of the Xcode.app in Applications, by using the "xcode-select" command from macOS Terminal:

 

sudo xcode-select -s /Applications/Xcode.app

Where "/Applications/XCode.app" is the location of your XCode 9 application. This command will require an administrator password.

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/243868-mex-can-t-find-compiler-after-xcode-7-update-r2015b#comment_454130 for the configuration file you need for XCode on Sierra; the location to install to is given in my comment two up from that one.

You will probably need to edit the files to copy the two lines with MacOSX10.12 and modify the copy to refer to MacOSX10.13