nixpkgs-basic-release-checks: check for case-insensitive path conflicts

pkgs/top-level/nixpkgs-basic-release-checks.nix

@@ -19,6 +19,14 @@ pkgs.runCommand "nixpkgs-release-checks" { src = nixpkgs; buildInputs = [nix]; }
         exit 1
     fi
 
+    # Make sure that no paths collide on case-preserving or case-insensitive filesysytems.
+    conflictingPaths=$(find $src | awk '{ print $1 " " tolower($1) }' | sort -k2 | uniq -D -f 1 | cut -d ' ' -f 1)
+    if [[ -n $conflictingPaths ]]; then
+        echo "Files in nixpkgs must not vary only by case"
+        echo "The offending paths: $conflictingPaths"
+        exit 1
+    fi
+
     src2=$TMPDIR/foo
     cp -rd $src $src2