derive: escape strings at compile-time when possible

Author: Kijewski

rinja_derive/src/generator.rs

@@ -14,6 +14,7 @@ use quote::quote;
 
 use crate::config::WhitespaceHandling;
 use crate::heritage::{Context, Heritage};
+use crate::html::write_escaped_str;
 use crate::input::{Source, TemplateInput};
 use crate::{CompileError, MsgValidEscapers, CRATE};
 
@@ -1161,8 +1162,43 @@ impl<'a> Generator<'a> {
     }
 
     fn write_expr(&mut self, ws: Ws, s: &'a WithSpan<'a, Expr<'a>>) {
+        let mut writable = Writable::Expr(s);
+        (|| {
+            let &Expr::StrLit(input) = &**s else {
+                return;
+            };
+
+            let Some(escaper) = self.input.escaper.strip_prefix(CRATE) else {
+                return;
+            };
+            let is_html = match escaper {
+                "::filters::Html" => true,
+                "::filters::Text" => false,
+                _ => return,
+            };
+
+            // TODO: implement parsing properly
+            let input = format!(r#""{input}""#);
+            let Ok(input) = input.parse::<proc_macro2::TokenStream>() else {
+                return;
+            };
+            let Ok(input) = syn::parse2::<syn::LitStr>(input) else {
+                return;
+            };
+            let input = input.value();
+
+            if is_html {
+                let mut escaped = String::with_capacity(input.len() + 20);
+                if write_escaped_str(&mut escaped, &input).is_ok() {
+                    writable = Writable::Lit(Cow::Owned(escaped));
+                }
+            } else {
+                writable = Writable::Lit(Cow::Owned(input));
+            }
+        })();
+
         self.handle_ws(ws);
-        self.buf_writable.push(Writable::Expr(s));
+        self.buf_writable.push(writable);
     }
 
     // Write expression buffer and empty

rinja_derive/src/tests.rs

@@ -346,25 +346,13 @@ writer.write_str("12")?;
         r#"writer.write_str("The card is")?;
         match &self.suit {
             Suit::Clubs | Suit::Spades => {
-                match (
-                    &((&&::rinja::filters::AutoEscaper::new(&(" black"), ::rinja::filters::Text)).rinja_auto_escape()?),
-                ) {
-                    (expr0,) => {
-                        (&&::rinja::filters::Writable(expr0)).rinja_write(writer)?;
-                    }
-                }
-             }
-             Suit::Diamonds | Suit::Hearts => {
-                match (
-                    &((&&::rinja::filters::AutoEscaper::new(&(" red"), ::rinja::filters::Text)).rinja_auto_escape()?),
-                ) {
-                    (expr0,) => {
-                        (&&::rinja::filters::Writable(expr0)).rinja_write(writer)?;
-                    }
-                }
+                writer.write_str(" black")?;
+            }
+            Suit::Diamonds | Suit::Hearts => {
+                writer.write_str(" red")?;
             }
         }"#,
         &[("suit", "Suit")],
-        14,
+        16,
     );
 }