Add askama::filter_fn proc-macro for custom filters with named/optional arg support

askama/Cargo.toml

@@ -45,15 +45,14 @@ maintenance = { status = "actively-developed" }
 
 [features]
 default = ["config", "derive", "std", "urlencode"]
-full = ["default", "blocks", "code-in-doc", "serde_json"]
+full = ["default", "code-in-doc", "serde_json"]
 
 alloc = [
     "askama_macros?/alloc",
     "serde?/alloc",
     "serde_json?/alloc",
     "percent-encoding?/alloc",
 ]
-blocks = ["askama_macros?/blocks"]
 code-in-doc = ["askama_macros?/code-in-doc"]
 config = ["askama_macros?/config"]
 derive = ["dep:askama_macros", "dep:askama_macros"]

askama/src/filters/escape.rs

@@ -256,6 +256,7 @@ impl<'a, T: HtmlSafe + ?Sized> AutoEscape for &AutoEscaper<'a, T, Html> {
 ///     use askama::{filters::MaybeSafe, Result, Values};
 ///
 ///     // Do not actually use this filter! It's an intentionally bad example.
+///     #[askama::filter_fn]
 ///     pub fn backdoor<T: std::fmt::Display>(
 ///         s: T,
 ///         _: &dyn Values,
@@ -386,6 +387,7 @@ const _: () = {
 ///     use askama::{filters::Safe, Result, Values};
 ///
 ///     // Do not actually use this filter! It's an intentionally bad example.
+///     #[askama::filter_fn]
 ///     pub fn strip_except_apos(s: impl ToString, _: &dyn Values) -> Result<Safe<String>> {
 ///         Ok(Safe(s
 ///             .to_string()

askama/src/filters/mod.rs

@@ -48,3 +48,14 @@ pub use self::urlencode::{urlencode, urlencode_strict};
 
 // MAX_LEN is maximum allowed length for filters.
 const MAX_LEN: usize = 10_000;
+
+/// Internal trait that is used by the `filter_fn` proc-macro to produce nicer error messages when
+/// too many arguments were passed to a filter invocation.
+#[doc(hidden)]
+#[diagnostic::on_unimplemented(
+    message = "Argument at position {IDX} is invalid on filter {Self}. Too many arguments supplied?",
+    label = "Filter function"
+)]
+pub trait ValidArgIdx<const IDX: usize> {
+    const VALID: bool = true;
+}

askama/src/lib.rs

@@ -82,6 +82,8 @@ use std::io;
 
 #[cfg(feature = "derive")]
 pub use askama_macros::Template;
+#[cfg(feature = "derive")]
+pub use askama_macros::filter_fn;
 
 pub use crate::error::{Error, Result};
 pub use crate::helpers::PrimitiveType;

askama_derive/Cargo.toml

@@ -30,20 +30,18 @@ memchr = "2"
 proc-macro2 = { version = "1", default-features = false }
 quote = { version = "1", default-features = false }
 rustc-hash = "2.0.0"
-syn = { version = "2.0.3", default-features = false, features = ["clone-impls", "derive", "parsing", "printing"] }
+syn = { version = "2.0.3", default-features = false, features = ["clone-impls", "derive", "full", "parsing", "printing"] }
 
 [dev-dependencies]
 console = "0.16.0"
 criterion = "0.7"
 prettyplease = "0.2.20"
 similar = "2.6.0"
-syn = { version = "2.0.3", features = ["full"] }
 
 [features]
 # Use every feature to aid testing. `askama_macros` will opt-out of default features.
 default = [
     "alloc",
-    "blocks",
     "code-in-doc",
     "config",
     "external-sources",
@@ -54,7 +52,6 @@ default = [
 ]
 
 alloc = []
-blocks = ["syn/full"]
 code-in-doc = ["dep:pulldown-cmark"]
 config = [
     "external-sources",