Add optional support for yaml filter (see #192)

3 files changed, 54 insertions, 3 deletions

diff --git a/askama_shared/src/error.rs b/askama_shared/src/error.rs
index bd35126..f3e8b48 100644
--- a/askama_shared/src/error.rs
+++ b/askama_shared/src/error.rs
@@ -32,6 +32,10 @@ pub enum Error {
     #[cfg(feature = "serde_json")]
     Json(::serde_json::Error),
 
+    /// yaml conversion error
+    #[cfg(feature = "serde_yaml")]
+    Yaml(::serde_yaml::Error),
+
     /// This error needs to be non-exhaustive as
     /// the `Json` variants existence depends on
     /// a feature.
@@ -54,6 +58,8 @@ impl ErrorTrait for Error {
             Error::Fmt(ref err) => err.source(),
             #[cfg(feature = "serde_json")]
             Error::Json(ref err) => err.source(),
+            #[cfg(feature = "serde_yaml")]
+            Error::Yaml(ref err) => err.source(),
             _ => None,
         }
     }
@@ -63,9 +69,10 @@ impl Display for Error {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             Error::Fmt(ref err) => write!(formatter, "formatting error: {}", err),
-
             #[cfg(feature = "serde_json")]
             Error::Json(ref err) => write!(formatter, "json conversion error: {}", err),
+            #[cfg(feature = "serde_yaml")]
+            Error::Yaml(ref err) => write!(formatter, "yaml conversion error: {}", err),
             _ => write!(formatter, "unknown error: __Nonexhaustive"),
         }
     }
@@ -84,6 +91,13 @@ impl From<::serde_json::Error> for Error {
     }
 }
 
+#[cfg(feature = "serde_yaml")]
+impl From<::serde_yaml::Error> for Error {
+    fn from(err: ::serde_yaml::Error) -> Self {
+        Error::Yaml(err)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::Error;
diff --git a/askama_shared/src/filters/mod.rs b/askama_shared/src/filters/mod.rs
index ea702db..7e7bc40 100644
--- a/askama_shared/src/filters/mod.rs
+++ b/askama_shared/src/filters/mod.rs
@@ -6,10 +6,14 @@
 
 #[cfg(feature = "serde_json")]
 mod json;
-
 #[cfg(feature = "serde_json")]
 pub use self::json::json;
 
+#[cfg(feature = "serde_yaml")]
+mod yaml;
+#[cfg(feature = "serde_yaml")]
+pub use self::yaml::yaml;
+
 use crate::error::Error::Fmt;
 use askama_escape::{Escaper, MarkupDisplay};
 use humansize::{file_size_opts, FileSize};
@@ -23,7 +27,7 @@ use super::Result;
 // Askama or should refer to a local `filters` module. It should contain all the
 // filters shipped with Askama, even the optional ones (since optional inclusion
 // in the const vector based on features seems impossible right now).
-pub const BUILT_IN_FILTERS: [&str; 22] = [
+pub const BUILT_IN_FILTERS: [&str; 23] = [
     "abs",
     "capitalize",
     "center",
@@ -46,6 +50,7 @@ pub const BUILT_IN_FILTERS: [&str; 22] = [
     "uppercase",
     "wordcount",
     "json", // Optional feature; reserve the name anyway
+    "yaml", // Optional feature; reserve the name anyway
 ];
 
 /// Marks a string (or other `Display` type) as safe
diff --git a/askama_shared/src/filters/yaml.rs b/askama_shared/src/filters/yaml.rs
new file mode 100644
index 0000000..fdd03f6
--- /dev/null
+++ b/askama_shared/src/filters/yaml.rs
@@ -0,0 +1,32 @@
+use crate::error::{Error, Result};
+use askama_escape::{Escaper, MarkupDisplay};
+use serde::Serialize;
+
+/// Serialize to JSON (requires `serde_json` feature)
+///
+/// ## Errors
+///
+/// This will panic if `S`'s implementation of `Serialize` decides to fail,
+/// or if `T` contains a map with non-string keys.
+pub fn yaml<E: Escaper, S: Serialize>(e: E, s: &S) -> Result<MarkupDisplay<E, String>> {
+    match serde_yaml::to_string(s) {
+        Ok(s) => Ok(MarkupDisplay::new_safe(s, e)),
+        Err(e) => Err(Error::from(e)),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use askama_escape::Html;
+
+    #[test]
+    fn test_yaml() {
+        assert_eq!(yaml(Html, &true).unwrap().to_string(), "---\ntrue");
+        assert_eq!(yaml(Html, &"foo").unwrap().to_string(), "---\nfoo");
+        assert_eq!(
+            yaml(Html, &vec!["foo", "bar"]).unwrap().to_string(),
+            "---\n- foo\n- bar"
+        );
+    }
+}