fmt: keep empty lines in const blocks (#9071)

vlib/v/checker/checker.v

@@ -2448,7 +2448,11 @@ pub fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 	for i, field in node.fields {
 		// TODO Check const name once the syntax is decided
 		if field.name in c.const_names {
-			c.error('duplicate const `$field.name`', field.pos)
+			name_pos := token.Position{
+				...field.pos
+				len: util.no_cur_mod(field.name, c.mod).len
+			}
+			c.error('duplicate const `$field.name`', name_pos)
 		}
 		c.const_names << field.name
 		field_names << field.name

vlib/v/fmt/fmt.v

@@ -310,12 +310,16 @@ pub fn (f Fmt) imp_stmt_str(imp ast.Import) string {
 	return '$imp.mod$imp_alias_suffix'
 }
 
-fn (f Fmt) should_insert_newline_before_stmt(stmt ast.Stmt, prev_stmt ast.Stmt) bool {
-	prev_line_nr := prev_stmt.position().last_line
+fn (f Fmt) should_insert_newline_before_node(node ast.Node, prev_node ast.Node) bool {
 	// No need to insert a newline if there is already one
 	if f.out.last_n(2) == '\n\n' {
 		return false
 	}
+	prev_line_nr := prev_node.position().last_line
+	// The nodes are Stmts
+	if node is ast.Stmt && prev_node is ast.Stmt {
+		stmt := node as ast.Stmt
+		prev_stmt := prev_node as ast.Stmt
 		// Force a newline after a block of HashStmts
 		if prev_stmt is ast.HashStmt && stmt !is ast.HashStmt && stmt !is ast.ExprStmt {
 			return true
@@ -327,9 +331,9 @@ fn (f Fmt) should_insert_newline_before_stmt(stmt ast.Stmt, prev_stmt ast.Stmt)
 			}
 		}
 		// The stmt shouldn't have a newline before
-	if stmt.position().line_nr - prev_line_nr <= 1 {
-		return false
-	}
+		// 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
@@ -345,6 +349,11 @@ fn (f Fmt) should_insert_newline_before_stmt(stmt ast.Stmt, prev_stmt ast.Stmt)
 				return false
 			}
 		}
+	}
+	// The node shouldn't have a newline before
+	if node.position().line_nr - prev_line_nr <= 1 {
+		return false
+	}
 	return true
 }
 
@@ -352,7 +361,7 @@ pub fn (mut f Fmt) stmts(stmts []ast.Stmt) {
 	mut prev_stmt := if stmts.len > 0 { stmts[0] } else { ast.Stmt{} }
 	f.indent++
 	for stmt in stmts {
-		if !f.pref.building_v && f.should_insert_newline_before_stmt(stmt, prev_stmt) {
+		if !f.pref.building_v && f.should_insert_newline_before_node(stmt, prev_stmt) {
 			f.out.writeln('')
 		}
 		f.stmt(stmt)
@@ -2241,13 +2250,17 @@ pub fn (mut f Fmt) const_decl(it ast.ConstDecl) {
 		}
 	}
 	f.indent++
+	mut prev_field := if it.fields.len > 0 { ast.Node(it.fields[0]) } else { ast.Node{} }
 	for field in it.fields {
-		comments := field.comments
-		mut j := 0
-		for j < comments.len && comments[j].pos.pos < field.pos.pos {
-			f.comment(comments[j], inline: true)
+		if field.comments.len > 0 {
+			if f.should_insert_newline_before_node(ast.Expr(field.comments[0]), prev_field) {
+				f.writeln('')
+			}
+			f.comments(field.comments, inline: true)
+			prev_field = ast.Expr(field.comments.last())
+		}
+		if f.should_insert_newline_before_node(field, prev_field) {
 			f.writeln('')
-			j++
 		}
 		name := field.name.after('.')
 		f.write('$name ')
@@ -2255,6 +2268,7 @@ pub fn (mut f Fmt) const_decl(it ast.ConstDecl) {
 		f.write('= ')
 		f.expr(field.expr)
 		f.writeln('')
+		prev_field = field
 	}
 	f.comments_after_last_field(it.end_comments)
 	f.indent--

vlib/v/fmt/tests/empty_lines_keep.vv

@@ -1,3 +1,26 @@
+// Keep empty lines in const blocks
+const (
+	_ = SomeStruct{
+		val: 'Multiline field exprs should cause no problems'
+	}
+	_ = 1
+
+	_ = 'Keep this empty line before'
+	// Comment before a field
+	_ = 2
+
+	// The empty line above should stay too
+	_ = 3
+
+	// This comment doesn't really belong anywhere
+
+	_ = 'A multiline string with a StringInterLiteral...
+	$foo
+	...and the ending brace on a newline had a wrong pos.last_line.
+	'
+	_ = 4
+)
+
 fn keep_single_empty_line() {
 	println('a')
 	println('b')

vlib/v/parser/parser.v

@@ -1772,7 +1772,7 @@ fn (mut p Parser) string_expr() ast.Expr {
 		fills: fills
 		fmts: fmts
 		fmt_poss: fposs
-		pos: pos
+		pos: pos.extend(p.prev_tok.position())
 	}
 	// need_fmts: prelimery - until checker finds out if really needed
 	p.inside_str_interp = false
@@ -2012,12 +2012,6 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 	const_pos := p.tok.position()
 	p.check(.key_const)
 	is_block := p.tok.kind == .lpar
-	/*
-	if p.tok.kind != .lpar {
-		p.error_with_pos('const declaration is missing parentheses `( ... )`', const_pos)
-		return ast.ConstDecl{}
-	}
-	*/
 	if is_block {
 		p.next() // (
 	}
@@ -2039,8 +2033,6 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 				pos)
 		}
 		full_name := p.prepend_mod(name)
-		// name := p.check_name()
-		// println('!!const: $name')
 		p.check(.assign)
 		if p.tok.kind == .key_fn {
 			p.error('const initializer fn literal is not a constant')
@@ -2052,7 +2044,7 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 			mod: p.mod
 			is_pub: is_pub
 			expr: expr
-			pos: pos
+			pos: pos.extend(expr.position())
 			comments: comments
 		}
 		fields << field