More useful error message and UI tests for missing escaper

rinja/src/filters/escape.rs

@@ -4,7 +4,7 @@ use std::str;
 
 /// Marks a string (or other `Display` type) as safe
 ///
-/// Use this is you want to allow markup in an expression, or if you know
+/// Use this if you want to allow markup in an expression, or if you know
 /// that the expression's contents don't need to be escaped.
 ///
 /// Rinja will automatically insert the first (`Escaper`) argument,

rinja_derive/src/generator.rs

@@ -1427,7 +1427,10 @@ impl<'a> Generator<'a> {
                         .contains(&Cow::Borrowed(name))
                         .then_some(path.as_ref())
                 })
-                .ok_or_else(|| ctx.generate_error("invalid escaper for escape filter", node))?,
+                .ok_or_else(|| ctx.generate_error(
+                    &format!("invalid escaper '{name}' for `escape` filter"),
+                    node,
+                ))?,
             None => self.input.escaper,
         };
         buf.write(format_args!("{CRATE}::filters::escape("));

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

@@ -0,0 +1,22 @@
+use rinja::Template;
+
+#[derive(Template)]
+#[template(
+    ext = "html",
+    source = r#"In LaTeX you write `{{text}}` like `{{text|escape("latex")}}`."#,
+)]
+struct LocalEscaper<'a> {
+    text: &'a str,
+}
+
+#[derive(Template)]
+#[template(
+    ext = "tex",
+    source = r#"In HTML you write `{{text}}` like `{{text|escape("html")}}`."#,
+)]
+struct GlobalEscaper<'a> {
+    text: &'a str,
+}
+
+fn main() {
+}

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

@@ -0,0 +1,17 @@
+error: invalid escaper 'latex' for `escape` filter
+ --> LocalEscaper.html:1:38
+       "text|escape(\"latex\")}}`."
+ --> tests/ui/no-such-escaper.rs:3:10
+  |
+3 | #[derive(Template)]
+  |          ^^^^^^^^
+  |
+  = 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'
+  --> tests/ui/no-such-escaper.rs:12:10
+   |
+12 | #[derive(Template)]
+   |          ^^^^^^^^
+   |
+   = note: this error originates in the derive macro `Template` (in Nightly builds, run with -Z macro-backtrace for more info)