liquid_lib/stdlib/blocks/
ifchanged_block.rs

1use std::io::Write;
2
3use liquid_core::error::{ResultLiquidExt, ResultLiquidReplaceExt};
4use liquid_core::Language;
5use liquid_core::Renderable;
6use liquid_core::Result;
7use liquid_core::Runtime;
8use liquid_core::Template;
9use liquid_core::{BlockReflection, ParseBlock, TagBlock, TagTokenIter};
10
11#[derive(Copy, Clone, Debug, Default)]
12pub struct IfChangedBlock;
13
14impl IfChangedBlock {
15    pub fn new() -> Self {
16        Self
17    }
18}
19
20impl BlockReflection for IfChangedBlock {
21    fn start_tag(&self) -> &str {
22        "ifchanged"
23    }
24
25    fn end_tag(&self) -> &str {
26        "endifchanged"
27    }
28
29    fn description(&self) -> &str {
30        ""
31    }
32}
33
34impl ParseBlock for IfChangedBlock {
35    fn parse(
36        &self,
37        mut arguments: TagTokenIter<'_>,
38        mut tokens: TagBlock<'_, '_>,
39        options: &Language,
40    ) -> Result<Box<dyn Renderable>> {
41        // no arguments should be supplied, trying to supply them is an error
42        arguments.expect_nothing()?;
43
44        let if_changed = Template::new(tokens.parse_all(options)?);
45
46        tokens.assert_empty();
47        Ok(Box::new(IfChanged { if_changed }))
48    }
49
50    fn reflection(&self) -> &dyn BlockReflection {
51        self
52    }
53}
54
55#[derive(Debug)]
56struct IfChanged {
57    if_changed: Template,
58}
59
60impl IfChanged {
61    fn trace(&self) -> String {
62        "{{% ifchanged %}}".to_owned()
63    }
64}
65
66impl Renderable for IfChanged {
67    fn render_to(&self, writer: &mut dyn Write, runtime: &dyn Runtime) -> Result<()> {
68        let mut rendered = Vec::new();
69        self.if_changed
70            .render_to(&mut rendered, runtime)
71            .trace_with(|| self.trace().into())?;
72
73        let rendered = String::from_utf8(rendered).expect("render only writes UTF-8");
74        if runtime
75            .registers()
76            .get_mut::<ChangedRegister>()
77            .has_changed(&rendered)
78        {
79            write!(writer, "{rendered}").replace("Failed to render")?;
80        }
81
82        Ok(())
83    }
84}
85
86/// Remembers the content of the last rendered `ifstate` block.
87#[derive(Debug, Clone, PartialEq, Eq, Default)]
88struct ChangedRegister {
89    last_rendered: Option<String>,
90}
91
92impl ChangedRegister {
93    /// Checks whether or not a new rendered `&str` is different from
94    /// `last_rendered` and updates `last_rendered` value to the new value.
95    fn has_changed(&mut self, rendered: &str) -> bool {
96        let has_changed = if let Some(last_rendered) = &self.last_rendered {
97            last_rendered != rendered
98        } else {
99            true
100        };
101        self.last_rendered = Some(rendered.to_owned());
102
103        has_changed
104    }
105}
106
107#[cfg(test)]
108mod test {
109    use super::*;
110
111    use liquid_core::parser;
112    use liquid_core::runtime::RuntimeBuilder;
113
114    use crate::stdlib;
115
116    fn options() -> Language {
117        let mut options = Language::default();
118        options
119            .blocks
120            .register("ifchanged".to_owned(), IfChangedBlock.into());
121        options
122            .blocks
123            .register("for".to_owned(), stdlib::ForBlock.into());
124        options
125            .blocks
126            .register("if".to_owned(), stdlib::IfBlock.into());
127        options
128    }
129
130    #[test]
131    fn test_ifchanged_block() {
132        let text = concat!(
133            "{% for a in (0..10) %}",
134            "{% ifchanged %}",
135            "\nHey! ",
136            "{% if a > 5 %}",
137            "Numbers are now bigger than 5!",
138            "{% endif %}",
139            "{% endifchanged %}",
140            "{% endfor %}",
141        );
142        let template = parser::parse(text, &options()).map(Template::new).unwrap();
143
144        let runtime = RuntimeBuilder::new().build();
145        let output = template.render(&runtime).unwrap();
146        assert_eq!(output, "\nHey! \nHey! Numbers are now bigger than 5!");
147    }
148}
liquid_lib/stdlib/blocks/ifchanged_block.rs

liquid_lib/stdlib/blocks/
ifchanged_block.rs
