feat(codegen): print inline legal comments (#7054)

part of https://github.com/oxc-project/oxc/issues/7050

crates/oxc_ast/src/ast/comment.rs

@@ -125,4 +125,19 @@ impl Comment {
     pub fn is_jsdoc(&self, source_text: &str) -> bool {
         self.is_leading() && self.is_block() && self.span.source_text(source_text).starts_with('*')
     }
+
+    /// Legal comments
+    ///
+    /// A "legal comment" is considered to be any statement-level comment
+    /// that contains `@license` or `@preserve` or that starts with `//!` or `/*!`.
+    /// <https://esbuild.github.io/api/#legal-comments>
+    pub fn is_legal(&self, source_text: &str) -> bool {
+        if !self.is_leading() {
+            return false;
+        }
+        let source_text = self.span.source_text(source_text);
+        source_text.starts_with('!')
+            || source_text.contains("@license")
+            || source_text.contains("@preserve")
+    }
 }

crates/oxc_codegen/src/comment.rs

@@ -44,34 +44,23 @@ impl<'a> Codegen<'a> {
         })
     }
 
-    /// Weather to keep leading comments.
-    fn is_leading_comments(&self, comment: &Comment) -> bool {
-        (comment.is_jsdoc(self.source_text) || (comment.is_line() && self.is_annotation_comment(comment)))
-            && comment.preceded_by_newline
-            // webpack comment `/*****/`
-            && !comment.span.source_text(self.source_text).chars().all(|c| c == '*')
+    fn is_annotation_comment(&self, comment: &Comment) -> bool {
+        let comment_content = comment.span.source_text(self.source_text);
+        ANNOTATION_MATCHER.find_iter(comment_content).count() != 0
     }
 
-    fn print_comment(&mut self, comment: &Comment) {
-        let comment_source = comment.real_span().source_text(self.source_text);
-        match comment.kind {
-            CommentKind::Line => {
-                self.print_str(comment_source);
-            }
-            CommentKind::Block => {
-                // Print block comments with our own indentation.
-                let lines = comment_source.split(is_line_terminator);
-                for line in lines {
-                    if !line.starts_with("/*") {
-                        self.print_indent();
-                    }
-                    self.print_str(line.trim_start());
-                    if !line.ends_with("*/") {
-                        self.print_hard_newline();
-                    }
-                }
-            }
-        }
+    fn is_legal_comment(&self, comment: &Comment) -> bool {
+        (self.options.comments || self.options.legal_comments.is_inline())
+            && comment.is_legal(self.source_text)
+    }
+
+    /// Weather to keep leading comments.
+    fn is_leading_comments(&self, comment: &Comment) -> bool {
+        comment.preceded_by_newline
+            && (comment.is_jsdoc(self.source_text)
+                || (comment.is_line() && self.is_annotation_comment(comment)))
+            && !comment.span.source_text(self.source_text).chars().all(|c| c == '*')
+        // webpack comment `/*****/`
     }
 
     pub(crate) fn print_leading_comments(&mut self, start: u32) {
@@ -81,40 +70,24 @@ impl<'a> Codegen<'a> {
         let Some(comments) = self.comments.remove(&start) else {
             return;
         };
-
         let (comments, unused_comments): (Vec<_>, Vec<_>) =
             comments.into_iter().partition(|comment| self.is_leading_comments(comment));
-
-        if comments.first().is_some_and(|c| c.preceded_by_newline) {
-            // Skip printing newline if this comment is already on a newline.
-            if self.last_byte().is_some_and(|b| b != b'\n' && b != b'\t') {
-                self.print_hard_newline();
-                self.print_indent();
-            }
-        }
-
-        for (i, comment) in comments.iter().enumerate() {
-            if i >= 1 && comment.preceded_by_newline {
-                self.print_hard_newline();
-                self.print_indent();
-            }
-
-            self.print_comment(comment);
-        }
-
-        if comments.last().is_some_and(|c| c.is_line() || c.followed_by_newline) {
-            self.print_hard_newline();
-            self.print_indent();
-        }
-
-        if !unused_comments.is_empty() {
-            self.comments.insert(start, unused_comments);
-        }
+        self.print_comments(start, &comments, unused_comments);
     }
 
-    fn is_annotation_comment(&self, comment: &Comment) -> bool {
-        let comment_content = comment.span.source_text(self.source_text);
-        ANNOTATION_MATCHER.find_iter(comment_content).count() != 0
+    /// A statement comment also includes legal comments
+    pub(crate) fn print_statement_comments(&mut self, start: u32) {
+        if self.options.minify {
+            return;
+        }
+        let Some(comments) = self.comments.remove(&start) else {
+            return;
+        };
+        let (comments, unused_comments): (Vec<_>, Vec<_>) =
+            comments.into_iter().partition(|comment| {
+                self.is_leading_comments(comment) || self.is_legal_comment(comment)
+            });
+        self.print_comments(start, &comments, unused_comments);
     }
 
     pub(crate) fn print_annotation_comments(&mut self, node_start: u32) {
@@ -168,4 +141,54 @@ impl<'a> Codegen<'a> {
             true
         }
     }
+
+    fn print_comments(&mut self, start: u32, comments: &[Comment], unused_comments: Vec<Comment>) {
+        if comments.first().is_some_and(|c| c.preceded_by_newline) {
+            // Skip printing newline if this comment is already on a newline.
+            if self.last_byte().is_some_and(|b| b != b'\n' && b != b'\t') {
+                self.print_hard_newline();
+                self.print_indent();
+            }
+        }
+
+        for (i, comment) in comments.iter().enumerate() {
+            if i >= 1 && comment.preceded_by_newline {
+                self.print_hard_newline();
+                self.print_indent();
+            }
+
+            self.print_comment(comment);
+        }
+
+        if comments.last().is_some_and(|c| c.is_line() || c.followed_by_newline) {
+            self.print_hard_newline();
+            self.print_indent();
+        }
+
+        if !unused_comments.is_empty() {
+            self.comments.insert(start, unused_comments);
+        }
+    }
+
+    fn print_comment(&mut self, comment: &Comment) {
+        let comment_source = comment.real_span().source_text(self.source_text);
+        match comment.kind {
+            CommentKind::Line => {
+                self.print_str(comment_source);
+            }
+            CommentKind::Block => {
+                // Print block comments with our own indentation.
+                let lines = comment_source.split(is_line_terminator);
+                for line in lines {
+                    if !line.starts_with("/*") {
+                        self.print_indent();
+                    }
+                    self.print_str(line.trim_start());
+                    if !line.ends_with("*/") {
+                        self.print_hard_newline();
+                    }
+                }
+            }
+        }
+    }
 }

crates/oxc_codegen/src/gen.rs

@@ -76,7 +76,7 @@ impl<'a> Gen for Directive<'a> {
 
 impl<'a> Gen for Statement<'a> {
     fn gen(&self, p: &mut Codegen, ctx: Context) {
-        p.print_leading_comments(self.span().start);
+        p.print_statement_comments(self.span().start);
         match self {
             Self::BlockStatement(stmt) => stmt.print(p, ctx),
             Self::BreakStatement(stmt) => stmt.print(p, ctx),

crates/oxc_codegen/src/lib.rs

@@ -33,7 +33,7 @@ use crate::{
 pub use crate::{
     context::Context,
     gen::{Gen, GenExpr},
-    options::CodegenOptions,
+    options::{CodegenOptions, LegalComment},
 };
 
 /// Code generator without whitespace removal.
@@ -190,7 +190,7 @@ impl<'a> Codegen<'a> {
         self.quote = if self.options.single_quote { b'\'' } else { b'"' };
         self.source_text = program.source_text;
         self.code.reserve(program.source_text.len());
-        if self.options.print_annotation_comments() {
+        if self.options.print_comments() {
             self.build_comments(&program.comments);
         }
         if let Some(path) = &self.options.source_map_path {

crates/oxc_codegen/src/options.rs

@@ -1,5 +1,30 @@
 use std::path::PathBuf;
 
+/// Legal comment
+///
+/// <https://esbuild.github.io/api/#legal-comments>
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
+pub enum LegalComment {
+    /// Do not preserve any legal comments (default).
+    #[default]
+    None,
+    /// Preserve all legal comments.
+    Inline,
+    /// Move all legal comments to the end of the file.
+    Eof,
+    /// Move all legal comments to a .LEGAL.txt file and link to them with a comment.
+    Linked,
+    /// Move all legal comments to a .LEGAL.txt file but to not link to them.
+    External,
+}
+
+impl LegalComment {
+    /// Is inline mode.
+    pub fn is_inline(self) -> bool {
+        self == Self::Inline
+    }
+}
+
 /// Codegen Options.
 #[derive(Debug, Clone)]
 pub struct CodegenOptions {
@@ -13,7 +38,7 @@ pub struct CodegenOptions {
     /// Default is `false`.
     pub minify: bool,
 
-    /// Print comments?
+    /// Print all comments?
     ///
     /// Default is `true`.
     pub comments: bool,
@@ -25,6 +50,15 @@ pub struct CodegenOptions {
     /// Default is `false`.
     pub annotation_comments: bool,
 
+    /// Print legal comments.
+    ///
+    /// Only takes into effect when `comments` is false.
+    ///
+    /// <https://esbuild.github.io/api/#legal-comments>
+    ///
+    /// Default is [LegalComment::None].
+    pub legal_comments: LegalComment,
+
     /// Override the source map path. This affects the `sourceMappingURL`
     /// comment at the end of the generated code.
     ///
@@ -40,12 +74,18 @@ impl Default for CodegenOptions {
             minify: false,
             comments: true,
             annotation_comments: false,
+            legal_comments: LegalComment::default(),
             source_map_path: None,
         }
     }
 }
 
 impl CodegenOptions {
+    pub(crate) fn print_comments(&self) -> bool {
+        !self.minify
+            && (self.comments || self.annotation_comments || self.legal_comments.is_inline())
+    }
+
     pub(crate) fn print_annotation_comments(&self) -> bool {
         !self.minify && (self.comments || self.annotation_comments)
     }

crates/oxc_codegen/tests/integration/legal_comments.rs

@@ -0,0 +1,15 @@
+use crate::snapshot;
+
+fn cases() -> Vec<&'static str> {
+    vec![
+        "/* @license */\n/* @license */\nfoo;bar;",
+        "/* @license */\n/* @preserve */\nfoo;bar;",
+        "/* @license */\n//! KEEP\nfoo;bar;",
+        "/* @license */\n/*! KEEP */\nfoo;bar;",
+    ]
+}
+
+#[test]
+fn legal_inline_comment() {
+    snapshot("legal_inline_comments", &cases());
+}

crates/oxc_codegen/tests/integration/main.rs

@@ -1,6 +1,7 @@
 #![allow(clippy::missing_panics_doc)]
 pub mod esbuild;
 pub mod jsdoc;
+pub mod legal_comments;
 pub mod pure_comments;
 pub mod tester;
 pub mod ts;
@@ -12,24 +13,32 @@ use oxc_parser::Parser;
 use oxc_span::SourceType;
 
 pub fn codegen(source_text: &str) -> String {
+    codegen_options(source_text, &CodegenOptions::default())
+}
+
+pub fn codegen_options(source_text: &str, options: &CodegenOptions) -> String {
     let allocator = Allocator::default();
     let source_type = SourceType::ts();
     let ret = Parser::new(&allocator, source_text, source_type).parse();
-    CodeGenerator::new()
-        .with_options(CodegenOptions { single_quote: true, ..CodegenOptions::default() })
-        .build(&ret.program)
-        .code
+    let mut options = options.clone();
+    options.single_quote = true;
+    CodeGenerator::new().with_options(options).build(&ret.program).code
 }
 
 pub fn snapshot(name: &str, cases: &[&str]) {
+    snapshot_options(name, cases, &CodegenOptions::default());
+}
+
+pub fn snapshot_options(name: &str, cases: &[&str], options: &CodegenOptions) {
     use std::fmt::Write;
 
     let snapshot = cases.iter().enumerate().fold(String::new(), |mut w, (i, case)| {
-        write!(w, "########## {i}\n{case}\n----------\n{}\n", codegen(case)).unwrap();
+        let result = codegen_options(case, options);
+        write!(w, "########## {i}\n{case}\n----------\n{result}\n",).unwrap();
         w
     });
 
-    insta::with_settings!({ prepend_module_to_snapshot => false, omit_expression => true }, {
+    insta::with_settings!({ prepend_module_to_snapshot => false, snapshot_suffix => "", omit_expression => true }, {
         insta::assert_snapshot!(name, snapshot);
     });
 }

crates/oxc_codegen/tests/integration/snapshots/legal_inline_comments.snap

@@ -0,0 +1,42 @@
+---
+source: crates/oxc_codegen/tests/integration/main.rs
+---
+########## 0
+/* @license */
+/* @license */
+foo;bar;
+----------
+/* @license */
+/* @license */
+foo;
+bar;
+
+########## 1
+/* @license */
+/* @preserve */
+foo;bar;
+----------
+/* @license */
+/* @preserve */
+foo;
+bar;
+
+########## 2
+/* @license */
+//! KEEP
+foo;bar;
+----------
+/* @license */
+//! KEEP
+foo;
+bar;
+
+########## 3
+/* @license */
+/*! KEEP */
+foo;bar;
+----------
+/* @license */
+/*! KEEP */
+foo;
+bar;