C++: Remove arguable FPs re: sizeof/decltype

Author: d10c

cpp/ql/src/Best Practices/Likely Errors/CommaBeforeMisleadingIndentation.ql

@@ -11,6 +11,7 @@
 import cpp
 import semmle.code.cpp.commons.Exclusions
 
+/** Gets the sub-expression of 'e' with the earliest-starting Location */
 Expr normalizeExpr(Expr e) {
   if exists(e.(Call).getQualifier())
   then result = normalizeExpr(e.(Call).getQualifier())
@@ -26,6 +27,12 @@ predicate isInLoopHead(CommaExpr ce) {
   ce.getEnclosingStmt() = any(ForStmt f).getInitialization()
 }
 
+predicate isInDecltypeOrSizeof(CommaExpr ce) {
+  ce.getParent*() instanceof SizeofExprOperator
+  or
+  ce.getParent*() = any(Decltype d).getExpr()
+}
+
 from CommaExpr ce, Expr left, Expr right, Location leftLoc, Location rightLoc
 where
   ce.fromSource() and
@@ -34,7 +41,8 @@ where
   right = normalizeExpr(ce.getRightOperand()) and
   leftLoc = left.getLocation() and
   rightLoc = right.getLocation() and
-  not isInLoopHead(ce) and // HACK to reduce FPs in loop heads; assumption: unlikely to be misread due to '(', ')' delimiters
+  not isInLoopHead(ce) and // <- HACK to reduce FPs in loop heads; assumption: unlikely to be misread due to '(', ')' delimiters
+  not isInDecltypeOrSizeof(ce) and // <- Removes arguable FPs since, like function calls (and loop heads), these Exprs have clear delimiters.
   leftLoc.getEndLine() < rightLoc.getStartLine() and
   leftLoc.getStartColumn() > rightLoc.getStartColumn()
 select right, "The indentation after the comma may be misleading (for some tab sizes)."

cpp/ql/test/query-tests/Best Practices/Likely Errors/CommaBeforeMisleadingIndentation/test.cpp

@@ -77,6 +77,10 @@ int test(int i, int j, int (*foo)(int), int (*bar)(int, int))
 	                   j++);
 	(void)sizeof(x.foo(i++), // GOOD
 	             j++);
+	using U = decltype(x.foo(i++), // GOOD? Unlikely to be misread
+				j++);
+	(void)sizeof(x.foo(i++), // GOOD? Unlikely to be misread
+				j++);
 
 	// Comma in loops
 
@@ -86,6 +90,11 @@ int test(int i, int j, int (*foo)(int), int (*bar)(int, int))
         i = j = i + j;
     }
 
+    while (i = foo(j++), // GOOD??? Currently ignoring loop heads
+        i != j && i != 42 && !foo(j)) {
+        i = j = i + j;
+    }
+
 	for (i = 0,         // GOOD? Currently ignoring loop heads.
 	    j = 1;
 		i + j < 10;