Add MsgValidEscapers to show list of configured escapers

rinja_derive/src/generator.rs

@@ -15,7 +15,7 @@ use quote::quote;
 use crate::config::WhitespaceHandling;
 use crate::heritage::{Context, Heritage};
 use crate::input::{Source, TemplateInput};
-use crate::{CompileError, CRATE};
+use crate::{CompileError, MsgValidEscapers, CRATE};
 
 pub(crate) struct Generator<'a> {
     // The template input state: original struct AST and attributes
@@ -1429,7 +1429,10 @@ impl<'a> Generator<'a> {
                 })
                 .ok_or_else(|| {
                     ctx.generate_error(
-                        &format!("invalid escaper '{name}' for `escape` filter"),
+                        &format!(
+                            "invalid escaper '{name}' for `escape` filter. {}",
+                            MsgValidEscapers(&self.input.config.escapers),
+                        ),
                         node,
                     )
                 })?,

rinja_derive/src/input.rs

@@ -10,7 +10,7 @@ use quote::ToTokens;
 use syn::punctuated::Punctuated;
 
 use crate::config::{get_template_source, Config};
-use crate::CompileError;
+use crate::{CompileError, MsgValidEscapers};
 
 pub(crate) struct TemplateInput<'a> {
     pub(crate) ast: &'a syn::DeriveInput,
@@ -87,7 +87,10 @@ impl TemplateInput<'_> {
                     .then_some(path.as_ref())
             })
             .ok_or_else(|| {
-                CompileError::no_file_info(format!("no escaper defined for extension '{escaping}'"))
+                CompileError::no_file_info(format!(
+                    "no escaper defined for extension '{escaping}'. {}",
+                    MsgValidEscapers(&config.escapers),
+                ))
             })?;
 
         let mime_type =

rinja_derive/src/lib.rs

@@ -8,6 +8,7 @@ mod input;
 #[cfg(test)]
 mod tests;
 
+use std::borrow::Cow;
 use std::collections::HashMap;
 use std::fmt;
 use std::path::Path;
@@ -231,6 +232,21 @@ impl fmt::Display for FileInfo<'_> {
     }
 }
 
+struct MsgValidEscapers<'a>(&'a [(Vec<Cow<'a, str>>, Cow<'a, str>)]);
+
+impl fmt::Display for MsgValidEscapers<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut exts = self
+            .0
+            .iter()
+            .flat_map(|(exts, _)| exts)
+            .map(|x| format!("{x:?}"))
+            .collect::<Vec<_>>();
+        exts.sort();
+        write!(f, "The available extensions are: {}", exts.join(", "))
+    }
+}
+
 // This is used by the code generator to decide whether a named filter is part of
 // Rinja or should refer to a local `filters` module. It should contain all the
 // filters shipped with Rinja, even the optional ones (since optional inclusion

testing/tests/ui/no-such-escaper.stderr

@@ -1,4 +1,4 @@
-error: invalid escaper 'latex' for `escape` filter
+error: invalid escaper 'latex' for `escape` filter. The available extensions are: "", "htm", "html", "j2", "jinja", "jinja2", "md", "none", "svg", "txt", "xml", "yml"
  --> LocalEscaper.html:1:38
        "text|escape(\"latex\")}}`."
  --> tests/ui/no-such-escaper.rs:3:10
@@ -8,7 +8,7 @@ error: invalid escaper 'latex' for `escape` filter
   |
   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: no escaper defined for extension 'tex'
+error: no escaper defined for extension 'tex'. The available extensions are: "", "htm", "html", "j2", "jinja", "jinja2", "md", "none", "svg", "txt", "xml", "yml"
   --> tests/ui/no-such-escaper.rs:12:10
    |
 12 | #[derive(Template)]