format: Fix panic with else blocks and comments

When an else block had a comment in between it and the rule body we
were not starting a new line, which triggers a panic in the formatter.

This corrects the issue, and also removes the panics. If the functions
are not called correctly the formatting will be off and tests will
fail. There is little benefit in them causing a panic.

Fixes: #2420
Signed-off-by: Patrick East <[email protected]>

format/format.go

@@ -308,6 +308,12 @@ func (w *writer) writeElse(rule *ast.Rule, comments []*ast.Comment) []*ast.Comme
 	rule.Else.Head.Args = nil
 	comments = w.insertComments(comments, rule.Else.Head.Location)
 
+	if hasCommentAbove && !wasInline {
+		// The comments would have ended the line, be sure to start one again
+		// before writing the rest of the "else" rule.
+		w.startLine()
+	}
+
 	// For backwards compatibility adjust the rule head value location
 	// TODO: Refactor the logic for inserting comments, or special
 	// case comments in a rule head value so this can be removed
@@ -1005,9 +1011,6 @@ func dedupComments(comments []*ast.Comment) []*ast.Comment {
 
 // startLine begins a line with the current indentation level.
 func (w *writer) startLine() {
-	if w.inline {
-		panic("currently in a line")
-	}
 	w.inline = true
 	for i := 0; i < w.level; i++ {
 		w.write(w.indent)
@@ -1016,9 +1019,6 @@ func (w *writer) startLine() {
 
 // endLine ends a line with a newline.
 func (w *writer) endLine() {
-	if !w.inline {
-		panic("not in a line")
-	}
 	w.inline = false
 	if w.beforeEnd != nil && !w.delay {
 		w.write(" " + w.beforeEnd.String())

format/testfiles/test_issue_2420.rego

@@ -0,0 +1,11 @@
+package example
+
+allow {
+    some_condition
+}
+
+# some comments
+
+else {
+    another_condition
+}

format/testfiles/test_issue_2420.rego.formatted

@@ -0,0 +1,11 @@
+package example
+
+allow {
+	some_condition
+}
+
+# some comments
+
+else {
+	another_condition
+}