Prevent duplicate case generation in generate_workflows.sh (NOAA-EMC#…

…3217)

This prevents generate_workflows.sh from generating multiple, identical
test cases.

Resolves NOAA-EMC#3213

workflow/generate_workflows.sh

@@ -17,13 +17,13 @@ function _usage() {
        directory up from this script's residing directory.
 
     -b Run build_all.sh with default flags
-       (build the UFS, UPP, UFS_Utils, and GFS-utils only
+       (build the UFS, UPP, UFS_Utils, and GFS-utils only)
 
     -u Update submodules before building and/or generating experiments.
 
     -y "list of YAMLs to run"
        If this option is not specified, the default case (C48_ATM) will be
-       run.  This option is overidden by -G or -E (see below).
+       run.  This option is incompatible with -G, -E, or -S.
        Example: -y "C48_ATM C48_S2SW C96C48_hybatmDA"
 
     -Y /path/to/directory/with/YAMLs
@@ -43,7 +43,6 @@ function _usage() {
        Run all valid SFS cases in the specified YAML directory.
 
     NOTES:
-         - Only one of -G -E or -S may be specified
          - Valid cases are determined by the experiment:system key as
            well as the skip_ci_on_hosts list in each YAML.
 
@@ -223,6 +222,22 @@ else
    done
 fi
 
+# Empty the _yaml_list array if -G, -E, and/or -S were selected
+if [[ "${_run_all_gfs}" == "true" || \
+      "${_run_all_gefs}" == "true" || \
+      "${_run_all_sfs}" == "true" ]]; then
+
+   # Raise an error if the user specified a yaml list and any of -G -E -S
+   if [[ "${_specified_yaml_list}" == "true" ]]; then
+      echo "Ambiguous case selection."
+      echo "Please select which tests to run explicitly with -y \"list of tests\" or"
+      echo "by specifying -G (all GFS), -E (all GEFS), and/or -S (all SFS), but not both."
+      exit 3
+   fi
+
+   _yaml_list=()
+fi
+
 # If -S is specified, exit (for now).
 # TODO when SFS tests come online, enable this option.
 if [[ "${_run_all_sfs}" == "true" ]]; then