Merge remote-tracking branch 'origin/topic/jsiwek/gh-955-prohibit-typecasting-switch-fallthrough'

* origin/topic/jsiwek/gh-955-prohibit-typecasting-switch-fallthrough:
  GH-955: Prohibit `fallthrough` in typecasting `switch` cases

Closes GH-955

CHANGES

@@ -1,4 +1,8 @@
 
+3.3.0-dev.238 | 2020-09-02 11:39:25 -0700
+
+  * GH-955: Prohibit `fallthrough` in typecasting `switch` cases (Jon Siwek, Corelight)
+
 3.3.0-dev.236 | 2020-09-01 22:33:05 -0700
 
   * Fix/finalize the generate-docs Github Action (Jon Siwek, Corelight)

VERSION

@@ -1 +1 @@
-3.3.0-dev.236
+3.3.0-dev.238

src/Stmt.cc

@@ -484,6 +484,23 @@ static StmtTag get_last_stmt_tag(const Stmt* stmt)
 	return get_last_stmt_tag(stmts->Stmts()[len - 1]);
 	}
 
+class FallthroughFinder : public TraversalCallback {
+	TraversalCode PreStmt(const Stmt* stmt) override
+		{
+		if ( stmt->Tag() == STMT_SWITCH )
+			// Don't search within nested switch-statements.
+			return TC_ABORTSTMT;
+
+		if ( stmt->Tag() != STMT_FALLTHROUGH )
+			return TC_CONTINUE;
+
+		reporter->PushLocation(stmt->GetLocationInfo());
+		reporter->Error("invalid 'fallthrough' in type-casting 'case' block");
+		reporter->PopLocation();
+		return TC_CONTINUE;
+		}
+};
+
 Case::Case(ListExprPtr arg_expr_cases, IDPList* arg_type_cases,
            StmtPtr arg_s)
 	: expr_cases(std::move(arg_expr_cases)), type_cases(arg_type_cases),
@@ -493,15 +510,27 @@ Case::Case(ListExprPtr arg_expr_cases, IDPList* arg_type_cases,
 
 	if ( t != STMT_BREAK && t != STMT_FALLTHROUGH && t != STMT_RETURN )
 		Error("case block must end in break/fallthrough/return statement");
+
+	if ( type_cases && Body() )
+		for ( const auto& id : *type_cases )
+			if ( id->Name() )
+				{
+				FallthroughFinder ff;
+				Body()->Traverse(&ff);
+				break;
+				}
 	}
 
 Case::~Case()
+	{
+	if ( type_cases )
 		{
 		for ( const auto& id : *type_cases )
 			Unref(id);
 
 		delete type_cases;
 		}
+	}
 
 void Case::Describe(ODesc* d) const
 	{

src/parse.y

@@ -1638,13 +1638,13 @@ case_list:
 
 case:
 		TOK_CASE expr_list ':' stmt_list
-			{ $$ = new zeek::detail::Case({zeek::AdoptRef{}, $2}, 0, {zeek::AdoptRef{}, $4}); }
+			{ $$ = new zeek::detail::Case({zeek::AdoptRef{}, $2}, nullptr, {zeek::AdoptRef{}, $4}); }
 	|
 		TOK_CASE case_type_list ':' stmt_list
 			{ $$ = new zeek::detail::Case(nullptr, $2, {zeek::AdoptRef{}, $4}); }
 	|
 		TOK_DEFAULT ':' stmt_list
-			{ $$ = new zeek::detail::Case(nullptr, 0, {zeek::AdoptRef{}, $3}); }
+			{ $$ = new zeek::detail::Case(nullptr, nullptr, {zeek::AdoptRef{}, $3}); }
 	;
 
 case_type_list:

testing/btest/Baseline/language.switch-type-cast-fallthrough-error/out

@@ -0,0 +1,3 @@
+error in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.switch-type-cast-fallthrough-error/switch-type-cast-fallthrough-error.zeek, line 9: invalid 'fallthrough' in type-casting 'case' block
+error in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.switch-type-cast-fallthrough-error/switch-type-cast-fallthrough-error.zeek, line 20: invalid 'fallthrough' in type-casting 'case' block
+error in /home/jon/pro/zeek/zeek/testing/btest/.tmp/language.switch-type-cast-fallthrough-error/switch-type-cast-fallthrough-error.zeek, line 22: invalid 'fallthrough' in type-casting 'case' block

testing/btest/language/switch-type-cast-fallthrough-error.zeek

@@ -0,0 +1,64 @@
+# @TEST-EXEC-FAIL: zeek -b %INPUT >out 2>&1
+# @TEST-EXEC:      TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff out
+
+local x: any = 0;
+
+switch ( x ) {
+case type count as i:
+	print "count", i;
+	fallthrough;  # This is invalid
+case type double as d:
+	print "double", d;
+	break;
+}
+
+switch ( x ) {
+case type count as i:
+	print "count", i;
+
+	if ( i == 0 )
+		fallthrough;  # This is invalid
+	else
+		fallthrough;  # This is invalid
+
+	break;
+case type double as d:
+	print "double", d;
+	break;
+}
+
+switch ( x ) {
+case type count as i:
+	print "count", i;
+
+	switch ( x as count ) {
+	case 0:
+		fallthrough;  # This is valid (inside nested switch statement)
+	case 1:
+		print "1";
+		break;
+	}
+
+	break;
+case type double as d:
+	print "double", d;
+	break;
+}
+
+switch ( x as count ) {
+case 0:
+	print "0";
+	fallthrough;
+case 1:
+	print "1";
+	break;
+}
+
+switch ( x ) {
+case type count:
+	print "count";
+	fallthrough;
+case type double:
+	print "double";
+	break;
+}