feat(es/minifier): support reduce_escaped_newline

crates/swc/src/lib.rs

@@ -914,7 +914,14 @@ impl Compiler {
                         .with_emit_assert_for_import_attributes(
                             opts.format.emit_assert_for_import_attributes,
                         )
-                        .with_inline_script(opts.format.inline_script),
+                        .with_inline_script(opts.format.inline_script)
+                        .with_reduce_escaped_newline(
+                            min_opts
+                                .compress
+                                .unwrap_or_default()
+                                .experimental
+                                .reduce_escaped_newline,
+                        ),
                     output: None,
                 },
             );

crates/swc_ecma_codegen/src/config.rs

@@ -2,6 +2,11 @@
 use serde::{Deserialize, Serialize};
 use swc_ecma_ast::EsVersion;
 
+#[cfg(feature = "serde-impl")]
+const fn true_by_default() -> bool {
+    true
+}
+
 #[derive(Debug, Clone, Copy)]
 #[cfg_attr(feature = "serde-impl", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde-impl", serde(rename_all = "camelCase"))]
@@ -39,6 +44,13 @@ pub struct Config {
 
     #[cfg_attr(feature = "serde-impl", serde(default))]
     pub inline_script: bool,
+
+    /// Transform escaped newline `'\n'` of `TplElement` to a newline character
+    /// to reduce text size of javascript code
+    ///
+    /// Defaults to `true`
+    #[cfg_attr(feature = "serde-impl", serde(default = "true_by_default"))]
+    pub reduce_escaped_newline: bool,
 }
 
 impl Default for Config {
@@ -50,6 +62,7 @@ impl Default for Config {
             omit_last_semi: false,
             emit_assert_for_import_attributes: false,
             inline_script: false,
+            reduce_escaped_newline: true,
         }
     }
 }
@@ -87,4 +100,13 @@ impl Config {
         self.inline_script = inline_script;
         self
     }
+
+    /// Transform escaped newline `'\n'` of `TplElement` to a newline character
+    /// to reduce text size of javascript code
+    ///
+    /// Defaults to `true`
+    pub fn with_reduce_escaped_newline(mut self, reduce_escaped_newline: bool) -> Self {
+        self.reduce_escaped_newline = reduce_escaped_newline;
+        self
+    }
 }

crates/swc_ecma_codegen/src/lib.rs

@@ -2023,7 +2023,11 @@ where
     fn emit_quasi(&mut self, node: &TplElement) -> Result {
         let raw = node.raw.replace("\r\n", "\n").replace('\r', "\n");
         if self.cfg.minify || (self.cfg.ascii_only && !node.raw.is_ascii()) {
-            let v = get_template_element_from_raw(&raw, self.cfg.ascii_only);
+            let v = get_template_element_from_raw(
+                &raw,
+                self.cfg.ascii_only,
+                self.cfg.reduce_escaped_newline,
+            );
             let span = node.span();
 
             let mut last_offset_gen = 0;
@@ -3811,7 +3815,11 @@ where
     }
 }
 
-fn get_template_element_from_raw(s: &str, ascii_only: bool) -> String {
+fn get_template_element_from_raw(
+    s: &str,
+    ascii_only: bool,
+    reduce_escaped_newline: bool,
+) -> String {
     fn read_escaped(
         radix: u32,
         len: Option<usize>,
@@ -3884,7 +3892,16 @@ fn get_template_element_from_raw(s: &str, ascii_only: bool) -> String {
         let unescape = match c {
             '\\' => match iter.next() {
                 Some(c) => match c {
-                    'n' => Some('\n'),
+                    'n' => {
+                        if reduce_escaped_newline {
+                            Some('\n')
+                        } else {
+                            buf.push('\\');
+                            buf.push('n');
+
+                            None
+                        }
+                    }
                     't' => Some('\t'),
                     'x' => {
                         read_escaped(16, Some(2), &mut buf, &mut iter);

crates/swc_ecma_codegen/tests/fixture.rs

@@ -1,5 +1,9 @@
-use std::path::{Path, PathBuf};
+use std::{
+    fs::read_to_string,
+    path::{Path, PathBuf},
+};
 
+use serde::Deserialize;
 use swc_ecma_ast::EsVersion;
 use swc_ecma_codegen::{
     text_writer::{JsWriter, WriteJs},
@@ -8,6 +12,42 @@ use swc_ecma_codegen::{
 use swc_ecma_parser::{parse_file_as_module, Syntax, TsSyntax};
 use testing::{run_test2, NormalizedOutput};
 
+const fn true_by_default() -> bool {
+    true
+}
+
+#[derive(Deserialize)]
+struct TestConfig {
+    #[serde(default = "true_by_default")]
+    reduce_escaped_newline: bool,
+}
+
+impl Default for TestConfig {
+    fn default() -> Self {
+        TestConfig {
+            reduce_escaped_newline: true,
+        }
+    }
+}
+
+fn find_config(dir: &Path) -> TestConfig {
+    let mut cur = Some(dir);
+    while let Some(dir) = cur {
+        let config = dir.join("config.json");
+        if config.exists() {
+            let config = read_to_string(&config).expect("failed to read config.json");
+            let config: TestConfig = serde_json::from_str(&config)
+                .expect("failed to deserialize value into a codegen config");
+
+            return config;
+        }
+
+        cur = dir.parent();
+    }
+
+    Default::default()
+}
+
 fn run(input: &Path, minify: bool) {
     let dir = input.parent().unwrap();
     let output = if minify {
@@ -23,6 +63,7 @@ fn run(input: &Path, minify: bool) {
     };
 
     run_test2(false, |cm, _| {
+        let config = find_config(dir);
         let fm = cm.load_file(input).unwrap();
 
         let m = parse_file_as_module(
@@ -49,7 +90,9 @@ fn run(input: &Path, minify: bool) {
             }
 
             let mut emitter = Emitter {
-                cfg: swc_ecma_codegen::Config::default().with_minify(minify),
+                cfg: swc_ecma_codegen::Config::default()
+                    .with_minify(minify)
+                    .with_reduce_escaped_newline(config.reduce_escaped_newline),
                 cm,
                 comments: None,
                 wr,

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/default/input.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/default/output.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/default/output.min.js

@@ -0,0 +1,5 @@
+const str="a\nb\nc";const tpl=`a
+${b}
+c`;const tpl2=`a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/disable/config.json

@@ -0,0 +1,3 @@
+{
+    "reduce_escaped_newline": false
+}

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/disable/input.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/disable/output.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/disable/output.min.js

@@ -0,0 +1,3 @@
+const str="a\nb\nc";const tpl=`a\n${b}\nc`;const tpl2=`a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/enable/config.json

@@ -0,0 +1,3 @@
+{
+    "reduce_escaped_newline": true
+}

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/enable/input.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/enable/output.js

@@ -0,0 +1,5 @@
+const str = "a\nb\nc";
+const tpl = `a\n${b}\nc`;
+const tpl2 = `a
+${b}
+c`;

crates/swc_ecma_codegen/tests/fixture/reduce-escaped-newline/enable/output.min.js

@@ -0,0 +1,5 @@
+const str="a\nb\nc";const tpl=`a
+${b}
+c`;const tpl2=`a
+${b}
+c`;

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

@@ -1872,6 +1872,8 @@ impl VisitMut for Optimizer<'_> {
             _ => {}
         }
 
+        self.reduce_escaped_newline_for_str_lit(e);
+
         #[cfg(feature = "trace-ast")]
         tracing::debug!("Output: {}", dump(e, true));
     }

crates/swc_ecma_minifier/src/compress/optimize/strings.rs

@@ -1,3 +1,4 @@
+use swc_atoms::Atom;
 use swc_common::{util::take::Take, Spanned, SyntaxContext};
 use swc_ecma_ast::*;
 use swc_ecma_utils::{ExprExt, Value::Known};
@@ -137,4 +138,40 @@ impl Optimizer<'_> {
             _ => {}
         }
     }
+
+    /// Convert string literals with escaped newline `'\n'` to template literal
+    /// with newline character.
+    pub(super) fn reduce_escaped_newline_for_str_lit(&mut self, expr: &mut Expr) {
+        if self.options.ecma < EsVersion::Es2015
+            || !self.options.experimental.reduce_escaped_newline
+        {
+            return;
+        }
+
+        if let Expr::Lit(Lit::Str(s)) = expr {
+            if s.value.contains('\n') {
+                *expr = Expr::Tpl(Tpl {
+                    span: s.span,
+                    exprs: Default::default(),
+                    quasis: vec![TplElement {
+                        span: s.span,
+                        cooked: Some(s.value.clone()),
+                        raw: convert_str_value_to_tpl_raw(&s.value),
+                        tail: true,
+                    }],
+                });
+                self.changed = true;
+                report_change!("strings: Reduced escaped newline for a string literal");
+            }
+        }
+    }
+}
+
+pub(super) fn convert_str_value_to_tpl_raw(value: &Atom) -> Atom {
+    value
+        .replace('\\', "\\\\")
+        .replace('`', "\\`")
+        .replace("${", "\\${")
+        .replace('\r', "\\r")
+        .into()
 }

crates/swc_ecma_minifier/src/option/mod.rs

@@ -123,6 +123,23 @@ impl Default for PureGetterOption {
     }
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
+#[non_exhaustive]
+pub struct CompressExperimentalOptions {
+    #[serde(default = "true_by_default")]
+    pub reduce_escaped_newline: bool,
+}
+
+impl Default for CompressExperimentalOptions {
+    fn default() -> Self {
+        CompressExperimentalOptions {
+            reduce_escaped_newline: true,
+        }
+    }
+}
+
 /// https://terser.org/docs/api-reference.html#compress-options
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "extra-serde", derive(Serialize, Deserialize))]
@@ -349,6 +366,9 @@ pub struct CompressOptions {
     /// Defaults to true.
     #[cfg_attr(feature = "extra-serde", serde(default = "true_by_default"))]
     pub pristine_globals: bool,
+
+    #[cfg_attr(feature = "extra-serde", serde(default))]
+    pub experimental: CompressExperimentalOptions,
 }
 
 impl CompressOptions {
@@ -442,6 +462,7 @@ impl Default for CompressOptions {
             unused: true,
             const_to_let: true,
             pristine_globals: true,
+            experimental: Default::default(),
         }
     }
 }