[analyzer] Teach scan-build to find /usr/bin/clang when installed in /usr/local/bin/

[dcoughlin]

Summary

Change scan-build on the Mac to support the scenario where scan-build is installed in
$TOOLCHAIN/usr/local/bin/ but clang itself is installed in $TOOLCHAIN/usr/bin/.

rdar://problem/48914634

[NoQ]

This should indeed take care of our relatively tricky macOS use-case! I'm a bit worried for unexpected consequences on some of the more exotic linux setups - who knows what ../.. is supposed to contain. Maybe restrict this lookup to Darwin somehow? - And i guess let's eventually consider supporting $PATH :)

[dcoughlin]

Update to restrict the new behavior to when Xcode is present.

[dcoughlin]

That's a good point. I've updated the patch to look for 'xcrun'

[NoQ]

Thx!

cfe/trunk/tools/scan-build/bin/scan-build

 sub ShellEscape {
   # copy argument to new variable so we don't clobber the original
   my $arg = shift || '';
   if ($arg =~ /["\s]/) { return "'" . $arg . "'"; }
   return $arg;
 }
 
 ##----------------------------------------------------------------------------##
+# FindXcrun - searches for the 'xcrun' executable. Returns "" if not found.
+##----------------------------------------------------------------------------##
+
+sub FindXcrun {
+  my $xcrun = `which xcrun`;
+  chomp $xcrun;
+  return $xcrun;
+}
+
+##----------------------------------------------------------------------------##
 # FindClang - searches for 'clang' executable.
 ##----------------------------------------------------------------------------##
 
 sub FindClang {
   if (!defined $Options{AnalyzerDiscoveryMethod}) {
     $Clang = Cwd::realpath("$RealBin/bin/clang") if (-f "$RealBin/bin/clang");
     if (!defined $Clang || ! -x $Clang) {
       $Clang = Cwd::realpath("$RealBin/clang") if (-f "$RealBin/clang");
+      if (!defined $Clang || ! -x $Clang) {
+        # When an Xcode toolchain is present, look for a clang in the sibling bin
+        # of the parent of the bin directory. So if scan-build is at
+        # $TOOLCHAIN/usr/local/bin/scan-build look for clang at
+        # $TOOLCHAIN/usr/bin/clang.
+        my $has_xcode_toolchain = FindXcrun() ne "";
+        if ($has_xcode_toolchain && -f "$RealBin/../../bin/clang") {
+          $Clang = Cwd::realpath("$RealBin/../../bin/clang");
+        }
+      }
     }
     if (!defined $Clang || ! -x $Clang) {
       return "error: Cannot find an executable 'clang' relative to" .
              " scan-build. Consider using --use-analyzer to pick a version of" .
              " 'clang' to use for static analysis.\n";
     }
   }
   else {
     if ($Options{AnalyzerDiscoveryMethod} =~ /^[Xx]code$/) {
-      my $xcrun = `which xcrun`;
-      chomp $xcrun;
+      my $xcrun = FindXcrun();
       if ($xcrun eq "") {
         return "Cannot find 'xcrun' to find 'clang' for analysis.\n";
       }
       $Clang = `$xcrun -toolchain XcodeDefault -find clang`;
       chomp $Clang;
       if ($Clang eq "") {
         return "No 'clang' executable found by 'xcrun'\n";
       }