Rust: Assume in the CFG that lowercase identifiers are in fact identifiers

Author: paldepind

rust/ql/lib/codeql/rust/controlflow/internal/Completion.qll

@@ -126,8 +126,11 @@ private predicate cannotCauseMatchFailure(Pat pat) {
   pat instanceof RangePat or
   // Identifier patterns that are in fact path patterns can cause failures. For
   // instance `None`. Only if an `@ ...` part is present can we be sure that
-  // it's an actual identifier pattern.
-  pat = any(IdentPat p | p.hasPat()) or
+  // it's an actual identifier pattern. As a heuristic, if the identifier starts
+  // with a lower case letter, then we assume that it's an identifier.  This
+  // works for code that follows the Rust naming convention for enums and
+  // constants.
+  pat = any(IdentPat p | p.hasPat() or p.getName().getText().charAt(0).isLowercase()) or
   pat instanceof WildcardPat or
   pat instanceof RestPat or
   pat instanceof RefPat or

rust/ql/test/library-tests/controlflow-unstable/Cfg.expected

@@ -19,7 +19,6 @@ edges
 | test.rs:6:17:6:31 | let ... = b | test.rs:6:31:6:31 | b |  |
 | test.rs:6:21:6:27 | Some(...) | test.rs:6:12:6:31 | [boolean(false)] ... && ... | no-match |
 | test.rs:6:21:6:27 | Some(...) | test.rs:6:26:6:26 | d | match |
-| test.rs:6:26:6:26 | d | test.rs:6:12:6:31 | [boolean(false)] ... && ... | no-match |
 | test.rs:6:26:6:26 | d | test.rs:6:12:6:31 | [boolean(true)] ... && ... | match |
 | test.rs:6:26:6:26 | d | test.rs:6:26:6:26 | d |  |
 | test.rs:6:31:6:31 | b | test.rs:6:21:6:27 | Some(...) |  |
@@ -47,7 +46,6 @@ edges
 | test.rs:14:12:15:16 | [boolean(false)] ... && ... | test.rs:19:13:19:17 | false | false |
 | test.rs:14:12:15:16 | [boolean(true)] ... && ... | test.rs:17:13:17:13 | d | true |
 | test.rs:14:17:14:25 | let ... = b | test.rs:14:25:14:25 | b |  |
-| test.rs:14:21:14:21 | d | test.rs:14:12:14:25 | [boolean(false)] ... && ... | no-match |
 | test.rs:14:21:14:21 | d | test.rs:14:12:14:25 | [boolean(true)] ... && ... | match |
 | test.rs:14:21:14:21 | d | test.rs:14:21:14:21 | d |  |
 | test.rs:14:25:14:25 | b | test.rs:14:21:14:21 | d |  |