Actions: Order command substitutions by their ID, not text

In the Bash parser, we compute a mostly-unique ID for each
command substitution within a shell script block.
Commands are then ranked and referred to individually.

Avoid a performance bottleneck by ranking commands by their
ID, not by their source text.
I think this was the original intent of the code.
Ranking by their original text ends up evaluating multiple
possible orderings, which is slow on workflows that contain
multiple complex command substitutions.

Author: adityasharad

actions/ql/lib/codeql/actions/Bash.qll

@@ -60,9 +60,12 @@ class BashShellScript extends ShellScript {
     )
   }
 
-  private predicate rankedCmdSubstitutionReplacements(int i, string old, string new) {
-    old = rank[i](string old2 | this.cmdSubstitutionReplacement(old2, _, _) | old2) and
-    this.cmdSubstitutionReplacement(old, new, _)
+  private predicate rankedCmdSubstitutionReplacements(int i, string command, string commandId) {
+    // rank commands by their unique IDs
+    commandId = rank[i](string c, string id | this.cmdSubstitutionReplacement(c, id, _) | id) and
+    // since we cannot output (command, ID) tuples from the rank operation,
+    // we need to work out the specific command associated with the resulting ID
+    this.cmdSubstitutionReplacement(command, commandId, _)
   }
 
   private predicate doReplaceCmdSubstitutions(int line, int round, string old, string new) {