JS: use guard nodes instead of synactic isConditional check

Author: asger-semmle

javascript/ql/src/Statements/UselessConditional.ql

@@ -115,25 +115,21 @@ predicate whitelist(Expr e) {
 }
 
 /**
- * Holds if `e` is part of a conditional node `cond` that evaluates
- * `e` and checks its value for truthiness.
+ * Gets the `&&` expression that defines this guard node, if any.
  */
-predicate isConditional(ASTNode cond, Expr e) {
-  e = cond.(IfStmt).getCondition() or
-  e = cond.(ConditionalExpr).getCondition() or
-  e = cond.(LogAndExpr).getLeftOperand() or
-  e = cond.(LogOrExpr).getLeftOperand()
+LogAndExpr getLogAndExpr(ConditionGuardNode guard) {
+  result.getLeftOperand().stripParens() = guard.getTest()
 }
 
-from ASTNode cond, DataFlow::AnalyzedNode op, boolean cv, ASTNode sel, string msg
-where isConditional(cond, op.asExpr()) and
+from ConditionGuardNode guard, DataFlow::AnalyzedNode op, boolean cv, ASTNode sel, string msg
+where guard.getTest() = op.asExpr() and
       cv = op.getTheBooleanValue()and
       not whitelist(op.asExpr()) and
 
       // if `cond` is of the form `<non-trivial truthy expr> && <something>`,
       // we suggest replacing it with `<non-trivial truthy expr>, <something>`
-      if cond instanceof LogAndExpr and cv = true and not op.asExpr().isPure() then
-        (sel = cond and msg = "This logical 'and' expression can be replaced with a comma expression.")
+      if exists(getLogAndExpr(guard)) and cv = true and not op.asExpr().isPure() then
+        (sel = getLogAndExpr(guard) and msg = "This logical 'and' expression can be replaced with a comma expression.")
 
       // otherwise we just report that `op` always evaluates to `cv`
       else (

javascript/ql/test/query-tests/Statements/UselessConditional/UselessConditional.expected

@@ -1,4 +1,4 @@
-| UselessConditional.js:5:7:5:12 | !lines | This expression always evaluates to false. |
+| UselessConditional.js:5:8:5:12 | lines | Variable 'lines' always evaluates to true here. |
 | UselessConditional.js:12:34:12:79 | (v = ne ... k] = v) | This logical 'and' expression can be replaced with a comma expression. |
 | UselessConditional.js:17:9:17:9 | a | Variable 'a' always evaluates to false here. |
 | UselessConditional.js:18:9:18:9 | b | Variable 'b' always evaluates to false here. |