fmt: respect user choice of newlines between functions without body (#8838)

vlib/v/fmt/fmt.v

@@ -304,18 +304,29 @@ pub fn (f Fmt) imp_stmt_str(imp ast.Import) string {
 
 fn (mut f Fmt) should_insert_newline_before_stmt(stmt ast.Stmt, prev_stmt ast.Stmt) bool {
 	prev_line_nr := prev_stmt.position().last_line
+	// No need to insert a newline if there is already one
+	if f.out.last_n(2) == '\n\n' {
+		return false
+	}
+	// Force a newline after a block of HashStmts
 	if prev_stmt is ast.HashStmt && stmt !is ast.HashStmt && stmt !is ast.ExprStmt {
 		return true
 	}
-	// The stmt either has or shouldn't have a newline before
-	if stmt.position().line_nr - prev_line_nr <= 1 || f.out.last_n(2) == '\n\n' {
+	// Force a newline after a block of function declarations
+	if prev_stmt is ast.FnDecl {
+		if prev_stmt.no_body && stmt !is ast.FnDecl {
+			return true
+		}
+	}
+	// The stmt shouldn't have a newline before
+	if stmt.position().line_nr - prev_line_nr <= 1 {
 		return false
 	}
 	// Imports are handled special hence they are ignored here
 	if stmt is ast.Import || prev_stmt is ast.Import {
 		return false
 	}
-	// Attributes are not respected in the stmts position, so we have to check it manually
+	// Attributes are not respected in the stmts position, so this requires a manual check
 	if stmt is ast.StructDecl {
 		if stmt.attrs.len > 0 && stmt.attrs[0].pos.line_nr - prev_line_nr <= 1 {
 			return false
@@ -640,7 +651,7 @@ pub fn (mut f Fmt) struct_decl(node ast.StructDecl) {
 		f.write('>')
 	}
 	if node.fields.len == 0 && node.embeds.len == 0 && node.pos.line_nr == node.pos.last_line {
-		f.writeln(' {}\n')
+		f.writeln(' {}')
 		return
 	}
 	f.writeln(' {')
@@ -1120,10 +1131,10 @@ pub fn (mut f Fmt) fn_decl(node ast.FnDecl) {
 			f.write('}')
 		}
 		if !node.is_anon {
-			f.writeln('\n')
+			f.writeln('')
 		}
 	} else {
-		f.writeln('\n')
+		f.writeln('')
 	}
 	// Mark all function's used type so that they are not removed from imports
 	for arg in node.params {

vlib/v/fmt/tests/newlines_keep.vv

@@ -2,6 +2,11 @@
 [manualfree]
 module websocket
 
+fn C.no_body_function()
+fn C.another_one(x int)
+
+fn C.separated_from_my_body_and_the_above()
+
 fn main() {}
 
 // This should stay between both functions
@@ -15,5 +20,5 @@ fn y_with_attr() {
 
 // doc comment above an attributed struct
 [typedef]
-struct Foo {
+struct FooWithAttr {
 }