feat(mangler): add debug mode (#4314)

closes #4303

crates/oxc_mangler/Cargo.toml

@@ -26,3 +26,9 @@ oxc_ast      = { workspace = true }
 oxc_semantic = { workspace = true }
 oxc_index    = { workspace = true }
 itertools    = { workspace = true }
+
+[dev-dependencies]
+oxc_allocator = { workspace = true }
+oxc_parser    = { workspace = true }
+oxc_codegen   = { workspace = true }
+pico-args     = { workspace = true }

crates/oxc_mangler/examples/mangler.rs

@@ -0,0 +1,43 @@
+#![allow(clippy::print_stdout)]
+use std::path::Path;
+
+use oxc_allocator::Allocator;
+use oxc_codegen::CodeGenerator;
+use oxc_mangler::ManglerBuilder;
+use oxc_parser::Parser;
+use oxc_span::SourceType;
+use pico_args::Arguments;
+
+// Instruction:
+// create a `test.js`,
+// run `cargo run -p oxc_mangler --example mangler` or `just example mangler`
+
+fn main() -> std::io::Result<()> {
+    let mut args = Arguments::from_env();
+
+    let name = args.subcommand().ok().flatten().unwrap_or_else(|| String::from("test.js"));
+    let debug = args.contains("--debug");
+    let twice = args.contains("--twice");
+
+    let path = Path::new(&name);
+    let source_text = std::fs::read_to_string(path)?;
+    let source_type = SourceType::from_path(path).unwrap();
+
+    let printed = mangler(&source_text, source_type, debug);
+    println!("{printed}");
+
+    if twice {
+        let printed = mangler(&printed, source_type, debug);
+        println!("{printed}");
+    }
+
+    Ok(())
+}
+
+fn mangler(source_text: &str, source_type: SourceType, debug: bool) -> String {
+    let allocator = Allocator::default();
+    let ret = Parser::new(&allocator, source_text, source_type).parse();
+    let program = allocator.alloc(ret.program);
+    let mangler = ManglerBuilder::default().debug(debug).build(program);
+    CodeGenerator::new().with_mangler(Some(mangler)).build(program).source_text
+}

crates/oxc_mangler/src/lib.rs

@@ -63,9 +63,18 @@ impl Mangler {
 ///     }
 /// }
 /// ```
-pub struct ManglerBuilder;
+#[derive(Debug, Default)]
+pub struct ManglerBuilder {
+    debug: bool,
+}
 
 impl ManglerBuilder {
+    #[must_use]
+    pub fn debug(mut self, yes: bool) -> Self {
+        self.debug = yes;
+        self
+    }
+
     #[must_use]
     pub fn build<'a>(self, program: &'a Program<'a>) -> Mangler {
         let semantic_ret = SemanticBuilder::new("", program.source_type).build(program);
@@ -119,10 +128,11 @@ impl ManglerBuilder {
 
         let mut names = Vec::with_capacity(total_number_of_slots);
 
+        let generate_name = if self.debug { debug_name } else { base54 };
         let mut count = 0;
         for _ in 0..total_number_of_slots {
             names.push(loop {
-                let name = base54(count);
+                let name = generate_name(count);
                 count += 1;
                 // Do not mangle keywords and unresolved references
                 if !is_keyword(&name) && !unresolved_references.iter().any(|n| **n == name) {
@@ -236,3 +246,7 @@ fn base54(n: usize) -> CompactStr {
     }
     CompactStr::new(&ret)
 }
+
+fn debug_name(n: usize) -> CompactStr {
+    CompactStr::from(format!("slot_{n}"))
+}

crates/oxc_minifier/src/lib.rs

@@ -41,7 +41,7 @@ impl Minifier {
 
     pub fn build<'a>(self, allocator: &'a Allocator, program: &mut Program<'a>) -> MinifierReturn {
         Compressor::new(allocator, self.options.compress).build(program);
-        let mangler = self.options.mangle.then(|| ManglerBuilder.build(program));
+        let mangler = self.options.mangle.then(|| ManglerBuilder::default().build(program));
         MinifierReturn { mangler }
     }
 }