tmpl: fix extra newline added on @if-@else-@end block (#22289)

vlib/v/parser/tmpl.v

@@ -327,37 +327,28 @@ fn vweb_tmpl_${fn_name}() string {
 			source.writeln(tmpl_str_end)
 			pos := line.index('@if') or { continue }
 			source.writeln('if ' + line[pos + 4..] + '{')
-			source.writeln(tmpl_str_start)
+			source.write_string(tmpl_str_start)
 			continue
 		}
 		if line.contains('@end') {
-			// Remove new line byte
-			source.go_back(1)
 			source.writeln(tmpl_str_end)
 			source.writeln('}')
-			source.writeln(tmpl_str_start)
+			source.write_string(tmpl_str_start)
 			continue
 		}
 		if line.contains('@else') {
-			// Remove new line byte
-			source.go_back(1)
 			source.writeln(tmpl_str_end)
 			pos := line.index('@else') or { continue }
 			source.writeln('}' + line[pos + 1..] + '{')
 			// source.writeln(' } else { ')
-			source.writeln(tmpl_str_start)
+			source.write_string(tmpl_str_start)
 			continue
 		}
 		if line.contains('@for') {
-			// Remove an extra unnecessary newline added before in state == .simple
-			// Can break stuff like Markdown
-			if source.len > 1 {
-				source.go_back(1)
-			}
 			source.writeln(tmpl_str_end)
 			pos := line.index('@for') or { continue }
 			source.writeln('for ' + line[pos + 4..] + '{')
-			source.writeln(tmpl_str_start)
+			source.write_string(tmpl_str_start)
 			continue
 		}
 		if state == .simple {
@@ -365,6 +356,7 @@ fn vweb_tmpl_${fn_name}() string {
 			source.writeln(insert_template_code(fn_name, tmpl_str_start, line))
 			continue
 		}
+		// in_write = false
 		// The .simple mode ends here. The rest handles .html/.css/.js state transitions.
 
 		if state != .simple {

vlib/v/tests/tmpl/if_cond.txt

@@ -0,0 +1,13 @@
+aaa
+@if cond
+bbb
+@else
+zzz
+@end
+ccc
+
+aaa
+@if cond
+bbb
+@end
+ccc

vlib/v/tests/tmpl_if_cond_test.v

@@ -0,0 +1,24 @@
+fn test_tmpl_if_cond() {
+	cond := true
+	processed := $tmpl('tmpl/if_cond.txt')
+	assert processed == 'aaa
+bbb
+ccc
+
+aaa
+bbb
+ccc
+'
+}
+
+fn test_tmpl_if_else_cond() {
+	cond := false
+	processed := $tmpl('tmpl/if_cond.txt')
+	assert processed == 'aaa
+zzz
+ccc
+
+aaa
+ccc
+'
+}

vlib/v/tests/tmpl_test.v

@@ -46,10 +46,8 @@ numbers: [1, 2, 3]
 vlang/ui, downloaded 3201 times.
 vlang/vtl, downloaded 123 times.
 
-
 this is not ignored
 
-
 so, it's basically true"
 
 	assert one().trim_space() == expected
@@ -86,10 +84,8 @@ numbers: [1, 2, 3]
 vlang/ui, downloaded 3201 times.
 vlang/vtl, downloaded 123 times.
 
-
 this is not ignored
 
-
 so, it's basically true"
 }