derive: escape strings at compile-time when possible

rinja/src/filters/escape.rs

@@ -1,6 +1,5 @@
 use std::convert::Infallible;
 use std::fmt::{self, Display, Formatter, Write};
-use std::num::NonZeroU8;
 use std::{borrow, str};
 
 /// Marks a string (or other `Display` type) as safe
@@ -83,69 +82,14 @@ pub fn e(text: impl fmt::Display, escaper: impl Escaper) -> Result<Safe<impl Dis
 pub struct Html;
 
 impl Escaper for Html {
-    fn write_escaped_str<W: Write>(&self, mut fmt: W, string: &str) -> fmt::Result {
-        let mut escaped_buf = *b"&#__;";
-        let mut last = 0;
-
-        for (index, byte) in string.bytes().enumerate() {
-            const MIN_CHAR: u8 = b'"';
-            const MAX_CHAR: u8 = b'>';
-
-            struct Table {
-                _align: [usize; 0],
-                lookup: [Option<[NonZeroU8; 2]>; (MAX_CHAR - MIN_CHAR + 1) as usize],
-            }
-
-            const TABLE: Table = {
-                const fn n(c: u8) -> Option<[NonZeroU8; 2]> {
-                    let n0 = match NonZeroU8::new(c / 10 + b'0') {
-                        Some(n) => n,
-                        None => panic!(),
-                    };
-                    let n1 = match NonZeroU8::new(c % 10 + b'0') {
-                        Some(n) => n,
-                        None => panic!(),
-                    };
-                    Some([n0, n1])
-                }
-
-                let mut table = Table {
-                    _align: [],
-                    lookup: [None; (MAX_CHAR - MIN_CHAR + 1) as usize],
-                };
-
-                table.lookup[(b'"' - MIN_CHAR) as usize] = n(b'"');
-                table.lookup[(b'&' - MIN_CHAR) as usize] = n(b'&');
-                table.lookup[(b'\'' - MIN_CHAR) as usize] = n(b'\'');
-                table.lookup[(b'<' - MIN_CHAR) as usize] = n(b'<');
-                table.lookup[(b'>' - MIN_CHAR) as usize] = n(b'>');
-                table
-            };
-
-            let escaped = match byte {
-                MIN_CHAR..=MAX_CHAR => TABLE.lookup[(byte - MIN_CHAR) as usize],
-                _ => None,
-            };
-            if let Some(escaped) = escaped {
-                escaped_buf[2] = escaped[0].get();
-                escaped_buf[3] = escaped[1].get();
-                fmt.write_str(&string[last..index])?;
-                fmt.write_str(unsafe { std::str::from_utf8_unchecked(escaped_buf.as_slice()) })?;
-                last = index + 1;
-            }
-        }
-        fmt.write_str(&string[last..])
+    #[inline]
+    fn write_escaped_str<W: Write>(&self, fmt: W, string: &str) -> fmt::Result {
+        crate::html::write_escaped_str(fmt, string)
     }
 
-    fn write_escaped_char<W: Write>(&self, mut fmt: W, c: char) -> fmt::Result {
-        fmt.write_str(match (c.is_ascii(), c as u8) {
-            (true, b'"') => "&#34;",
-            (true, b'&') => "&#38;",
-            (true, b'\'') => "&#39;",
-            (true, b'<') => "&#60;",
-            (true, b'>') => "&#62;",
-            _ => return fmt.write_char(c),
-        })
+    #[inline]
+    fn write_escaped_char<W: Write>(&self, fmt: W, c: char) -> fmt::Result {
+        crate::html::write_escaped_char(fmt, c)
     }
 }
 

rinja/src/html.rs

@@ -0,0 +1,71 @@
+use std::fmt;
+use std::num::NonZeroU8;
+
+#[allow(unused)]
+pub(crate) fn write_escaped_str(mut fmt: impl fmt::Write, string: &str) -> fmt::Result {
+    let mut escaped_buf = *b"&#__;";
+    let mut last = 0;
+
+    for (index, byte) in string.bytes().enumerate() {
+        let escaped = match byte {
+            MIN_CHAR..=MAX_CHAR => TABLE.lookup[(byte - MIN_CHAR) as usize],
+            _ => None,
+        };
+        if let Some(escaped) = escaped {
+            escaped_buf[2] = escaped[0].get();
+            escaped_buf[3] = escaped[1].get();
+            fmt.write_str(&string[last..index])?;
+            fmt.write_str(unsafe { std::str::from_utf8_unchecked(escaped_buf.as_slice()) })?;
+            last = index + 1;
+        }
+    }
+    fmt.write_str(&string[last..])
+}
+
+#[allow(unused)]
+pub(crate) fn write_escaped_char(mut fmt: impl fmt::Write, c: char) -> fmt::Result {
+    fmt.write_str(match (c.is_ascii(), c as u8) {
+        (true, b'"') => """,
+        (true, b'&') => "&",
+        (true, b'\'') => "'",
+        (true, b'<') => "&#60;",
+        (true, b'>') => "&#62;",
+        _ => return fmt.write_char(c),
+    })
+}
+
+const MIN_CHAR: u8 = b'"';
+const MAX_CHAR: u8 = b'>';
+
+struct Table {
+    _align: [usize; 0],
+    lookup: [Option<[NonZeroU8; 2]>; (MAX_CHAR - MIN_CHAR + 1) as usize],
+}
+
+const TABLE: Table = {
+    const fn n(c: u8) -> Option<[NonZeroU8; 2]> {
+        assert!(MIN_CHAR <= c && c <= MAX_CHAR);
+
+        let n0 = match NonZeroU8::new(c / 10 + b'0') {
+            Some(n) => n,
+            None => panic!(),
+        };
+        let n1 = match NonZeroU8::new(c % 10 + b'0') {
+            Some(n) => n,
+            None => panic!(),
+        };
+        Some([n0, n1])
+    }
+
+    let mut table = Table {
+        _align: [],
+        lookup: [None; (MAX_CHAR - MIN_CHAR + 1) as usize],
+    };
+
+    table.lookup[(b'"' - MIN_CHAR) as usize] = n(b'"');
+    table.lookup[(b'&' - MIN_CHAR) as usize] = n(b'&');
+    table.lookup[(b'\'' - MIN_CHAR) as usize] = n(b'\'');
+    table.lookup[(b'<' - MIN_CHAR) as usize] = n(b'<');
+    table.lookup[(b'>' - MIN_CHAR) as usize] = n(b'>');
+    table
+};

rinja/src/lib.rs

@@ -57,6 +57,7 @@
 mod error;
 pub mod filters;
 pub mod helpers;
+mod html;
 
 use std::{fmt, io};
 

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};
 
@@ -1162,8 +1163,76 @@ impl<'a> Generator<'a> {
     }
 
     fn write_expr(&mut self, ws: Ws, s: &'a WithSpan<'a, Expr<'a>>) {
+        // In here, we inspect in the expression if it is a literal, and if it is, whether it
+        // can be escaped at compile time. We use an IIFE to make the code more readable
+        // (immediate returns, try expressions).
+        let writable = (|| -> Option<Writable<'a>> {
+            enum InputKind<'a> {
+                StrLit(&'a str),
+                CharLit(&'a str),
+            }
+            enum OutputKind {
+                Html,
+                Text,
+            }
+
+            // for now, we only escape strings and chars at compile time
+            let lit = match &**s {
+                Expr::StrLit(input) => InputKind::StrLit(input),
+                Expr::CharLit(input) => InputKind::CharLit(input),
+                _ => return None,
+            };
+
+            // we only optimize for known escapers
+            let output = match self.input.escaper.strip_prefix(CRATE)? {
+                "::filters::Html" => OutputKind::Html,
+                "::filters::Text" => OutputKind::Text,
+                _ => return None,
+            };
+
+            // the input could be string escaped if it contains any backslashes
+            let escaped = match lit {
+                InputKind::StrLit(s) => s,
+                InputKind::CharLit(s) => s,
+            };
+            let unescaped = if escaped.find('\\').is_none() {
+                // if the literal does not contain any backslashes, then it does not need unescaping
+                Cow::Borrowed(escaped)
+            } else {
+                // convert the input into a TokenStream and extract the first token
+                Cow::Owned(match lit {
+                    InputKind::StrLit(escaped) => {
+                        let input = format!(r#""{escaped}""#);
+                        let input = input.parse().ok()?;
+                        let input = syn::parse2::<syn::LitStr>(input).ok()?;
+                        input.value()
+                    }
+                    InputKind::CharLit(escaped) => {
+                        let input = format!(r#"'{escaped}'"#);
+                        let input = input.parse().ok()?;
+                        let input = syn::parse2::<syn::LitChar>(input).ok()?;
+                        input.value().to_string()
+                    }
+                })
+            };
+
+            // escape the un-string-escaped input using the selected escaper
+            Some(Writable::Lit(match output {
+                OutputKind::Text => unescaped,
+                OutputKind::Html => {
+                    let mut escaped = String::with_capacity(unescaped.len() + 20);
+                    write_escaped_str(&mut escaped, &unescaped).ok()?;
+                    match escaped == unescaped {
+                        true => unescaped,
+                        false => Cow::Owned(escaped),
+                    }
+                }
+            }))
+        })()
+        .unwrap_or(Writable::Expr(s));
+
         self.handle_ws(ws);
-        self.buf_writable.push(Writable::Expr(s));
+        self.buf_writable.push(writable);
     }
 
     // Write expression buffer and empty
@@ -1174,7 +1243,7 @@ impl<'a> Generator<'a> {
     ) -> Result<usize, CompileError> {
         let mut size_hint = 0;
         let items = mem::take(&mut self.buf_writable.buf);
-        let mut it = items.into_iter().enumerate().peekable();
+        let mut it = items.iter().enumerate().peekable();
 
         while let Some((_, Writable::Lit(s))) = it.peek() {
             size_hint += buf.write_writer(s);
@@ -1267,20 +1336,23 @@ impl<'a> Generator<'a> {
                     assert!(rws.is_empty());
                     self.next_ws = Some(lws);
                 }
-                WhitespaceHandling::Preserve => self.buf_writable.push(Writable::Lit(lws)),
+                WhitespaceHandling::Preserve => {
+                    self.buf_writable.push(Writable::Lit(Cow::Borrowed(lws)))
+                }
                 WhitespaceHandling::Minimize => {
-                    self.buf_writable
-                        .push(Writable::Lit(match lws.contains('\n') {
+                    self.buf_writable.push(Writable::Lit(Cow::Borrowed(
+                        match lws.contains('\n') {
                             true => "\n",
                             false => " ",
-                        }));
+                        },
+                    )));
                 }
             }
         }
 
         if !val.is_empty() {
             self.skip_ws = WhitespaceHandling::Preserve;
-            self.buf_writable.push(Writable::Lit(val));
+            self.buf_writable.push(Writable::Lit(Cow::Borrowed(val)));
         }
 
         if !rws.is_empty() {
@@ -2031,17 +2103,18 @@ impl<'a> Generator<'a> {
             WhitespaceHandling::Preserve => {
                 let val = self.next_ws.unwrap();
                 if !val.is_empty() {
-                    self.buf_writable.push(Writable::Lit(val));
+                    self.buf_writable.push(Writable::Lit(Cow::Borrowed(val)));
                 }
             }
             WhitespaceHandling::Minimize => {
                 let val = self.next_ws.unwrap();
                 if !val.is_empty() {
-                    self.buf_writable
-                        .push(Writable::Lit(match val.contains('\n') {
+                    self.buf_writable.push(Writable::Lit(Cow::Borrowed(
+                        match val.contains('\n') {
                             true => "\n",
                             false => " ",
-                        }));
+                        },
+                    )));
                 }
             }
             WhitespaceHandling::Suppress => {}
@@ -2481,7 +2554,7 @@ impl<'a> Deref for WritableBuffer<'a> {
 
 #[derive(Debug)]
 enum Writable<'a> {
-    Lit(&'a str),
+    Lit(Cow<'a, str>),
     Expr(&'a WithSpan<'a, Expr<'a>>),
 }
 

rinja_derive/src/html.rs

@@ -0,0 +1 @@
+../../rinja/src/html.rs

rinja_derive/src/lib.rs

@@ -4,6 +4,7 @@
 mod config;
 mod generator;
 mod heritage;
+mod html;
 mod input;
 #[cfg(test)]
 mod tests;

rinja_derive/src/tests.rs

@@ -426,3 +426,38 @@ fn check_bool_conditions() {
         3,
     );
 }
+
+#[test]
+fn check_escaping_at_compile_time() {
+    compare(
+        r#"The card is
+        {%- match suit %}
+            {%- when Suit::Clubs or Suit::Spades -%}
+                {{ " black" }}
+            {%- when Suit::Diamonds or Suit::Hearts -%}
+                {{ " red" }}
+        {%- endmatch %}"#,
+        r#"writer.write_str("The card is")?;
+        match &self.suit {
+            Suit::Clubs | Suit::Spades => {
+                writer.write_str(" black")?;
+            }
+            Suit::Diamonds | Suit::Hearts => {
+                writer.write_str(" red")?;
+            }
+        }"#,
+        &[("suit", "Suit")],
+        16,
+    );
+
+    compare(
+        r#"{{ '\x41' }}{{ '\n' }}{{ '\r' }}{{ '\t' }}{{ '\\' }}{{ '\u{2665}' }}{{ '\'' }}{{ '\"' }}{{ '"' }}
+{{ "\x41\n\r\t\\\u{2665}\'\"'" }}"#,
+        r#"writer.write_str("A
+\r	\\♥'\"\"
+A
+\r	\\♥'\"'")?;"#,
+        &[],
+        23,
+    );
+}