Add method to lazily compute property source ranges (parcel-bundler#169)

Author: devongovett

src/declaration.rs

@@ -1,6 +1,7 @@
 //! CSS declarations.
 
 use std::borrow::Cow;
+use std::ops::Range;
 
 use crate::context::PropertyHandlerContext;
 use crate::error::{ParserError, PrinterError};
@@ -179,6 +180,43 @@ impl<'i> DeclarationBlock<'i> {
   pub fn is_empty(&self) -> bool {
     return self.declarations.is_empty() && self.important_declarations.is_empty();
   }
+
+  pub(crate) fn property_location<'t>(
+    &self,
+    input: &mut Parser<'i, 't>,
+    index: usize,
+  ) -> Result<(Range<SourceLocation>, Range<SourceLocation>), ParseError<'i, ParserError<'i>>> {
+    // Skip to the requested property index.
+    for _ in 0..index {
+      input.expect_ident()?;
+      input.expect_colon()?;
+      input.parse_until_after(Delimiter::Semicolon, |parser| {
+        while parser.next().is_ok() {}
+        Ok(())
+      })?;
+    }
+
+    // Get property name range.
+    input.skip_whitespace();
+    let key_start = input.current_source_location();
+    input.expect_ident()?;
+    let key_end = input.current_source_location();
+    let key_range = key_start..key_end;
+
+    input.expect_colon()?;
+    input.skip_whitespace();
+
+    // Get value range.
+    let val_start = input.current_source_location();
+    input.parse_until_before(Delimiter::Semicolon, |parser| {
+      while parser.next().is_ok() {}
+      Ok(())
+    })?;
+    let val_end = input.current_source_location();
+    let val_range = val_start..val_end;
+
+    Ok((key_range, val_range))
+  }
 }
 
 impl<'i> DeclarationBlock<'i> {

src/dependencies.rs

@@ -104,7 +104,7 @@ pub struct SourceRange {
   pub file_path: String,
   /// The starting line and column position of the dependency.
   pub start: Location,
-  /// THe ending line and column position of the dependency.
+  /// The ending line and column position of the dependency.
   pub end: Location,
 }
 

src/error.rs

@@ -36,7 +36,7 @@ pub struct ErrorLocation {
   pub filename: String,
   /// The line number, starting from 0.
   pub line: u32,
-  /// THe column number, starting from 1.
+  /// The column number, starting from 1.
   pub column: u32,
 }
 

src/lib.rs

@@ -51,6 +51,7 @@ mod tests {
   use crate::targets::Browsers;
   use crate::traits::{Parse, ToCss};
   use crate::values::color::CssColor;
+  use cssparser::SourceLocation;
   use indoc::indoc;
   use std::collections::HashMap;
 
@@ -17960,6 +17961,60 @@ mod tests {
       property.to_css_string(true, PrinterOptions::default()).unwrap(),
       "color: #f0f !important"
     );
+
+    let code = indoc! { r#"
+      .foo {
+        color: green;
+      }
+
+      .bar {
+        color: red;
+        background: pink;
+      }
+
+      @media print {
+        .baz {
+          color: green;
+        }
+      }
+    "#};
+    let stylesheet = StyleSheet::parse("test.css", code, ParserOptions::default()).unwrap();
+    if let CssRule::Style(style) = &stylesheet.rules.0[1] {
+      let (key, val) = style.property_location(code, 0).unwrap();
+      assert_eq!(
+        key,
+        SourceLocation { line: 5, column: 3 }..SourceLocation { line: 5, column: 8 }
+      );
+      assert_eq!(
+        val,
+        SourceLocation { line: 5, column: 10 }..SourceLocation { line: 5, column: 13 }
+      );
+    }
+
+    if let CssRule::Style(style) = &stylesheet.rules.0[1] {
+      let (key, val) = style.property_location(code, 1).unwrap();
+      assert_eq!(
+        key,
+        SourceLocation { line: 6, column: 3 }..SourceLocation { line: 6, column: 13 }
+      );
+      assert_eq!(
+        val,
+        SourceLocation { line: 6, column: 15 }..SourceLocation { line: 6, column: 19 }
+      );
+    }
+    if let CssRule::Media(media) = &stylesheet.rules.0[2] {
+      if let CssRule::Style(style) = &media.rules.0[0] {
+        let (key, val) = style.property_location(code, 0).unwrap();
+        assert_eq!(
+          key,
+          SourceLocation { line: 11, column: 5 }..SourceLocation { line: 11, column: 10 }
+        );
+        assert_eq!(
+          val,
+          SourceLocation { line: 11, column: 12 }..SourceLocation { line: 11, column: 17 }
+        );
+      }
+    }
   }
 
   #[test]

src/rules/style.rs

@@ -1,17 +1,21 @@
 //! Style rules.
 
+use std::ops::Range;
+
 use super::Location;
 use super::MinifyContext;
 use crate::compat::Feature;
 use crate::context::DeclarationContext;
 use crate::declaration::DeclarationBlock;
+use crate::error::ParserError;
 use crate::error::{MinifyError, PrinterError, PrinterErrorKind};
 use crate::printer::Printer;
 use crate::rules::{CssRuleList, StyleContext, ToCssWithContext};
 use crate::selector::{is_compatible, is_unused, Selectors};
 use crate::targets::Browsers;
 use crate::traits::ToCss;
 use crate::vendor_prefix::VendorPrefix;
+use cssparser::*;
 use parcel_selectors::SelectorList;
 
 /// A CSS [style rule](https://drafts.csswg.org/css-syntax/#style-rules).
@@ -74,6 +78,67 @@ impl<'i> StyleRule<'i> {
   pub fn is_compatible(&self, targets: Option<Browsers>) -> bool {
     is_compatible(&self.selectors, targets)
   }
+
+  /// Returns the line and column range of the property key and value at the given index in this style rule.
+  ///
+  /// For performance and memory efficiency in non-error cases, source locations are not stored during parsing.
+  /// Instead, they are computed lazily using the original source string that was used to parse the stylesheet/rule.
+  pub fn property_location<'t>(
+    &self,
+    code: &'i str,
+    index: usize,
+  ) -> Result<(Range<SourceLocation>, Range<SourceLocation>), ParseError<'i, ParserError<'i>>> {
+    let mut input = ParserInput::new(code);
+    let mut parser = Parser::new(&mut input);
+
+    // advance until start location of this rule.
+    parse_at(&mut parser, self.loc, |parser| {
+      // skip selector
+      parser.parse_until_before(Delimiter::CurlyBracketBlock, |parser| {
+        while parser.next().is_ok() {}
+        Ok(())
+      })?;
+
+      parser.expect_curly_bracket_block()?;
+      parser.parse_nested_block(|parser| {
+        let loc = self.declarations.property_location(parser, index);
+        while parser.next().is_ok() {}
+        loc
+      })
+    })
+  }
+}
+
+fn parse_at<'i, 't, T, F>(
+  parser: &mut Parser<'i, 't>,
+  dest: Location,
+  parse: F,
+) -> Result<T, ParseError<'i, ParserError<'i>>>
+where
+  F: Copy + for<'tt> FnOnce(&mut Parser<'i, 'tt>) -> Result<T, ParseError<'i, ParserError<'i>>>,
+{
+  loop {
+    let loc = parser.current_source_location();
+    if loc.line >= dest.line || (loc.line == dest.line && loc.column >= dest.column) {
+      return parse(parser);
+    }
+
+    match parser.next()? {
+      Token::CurlyBracketBlock => {
+        // Recursively parse nested blocks.
+        let res = parser.parse_nested_block(|parser| {
+          let res = parse_at(parser, dest, parse);
+          while parser.next().is_ok() {}
+          res
+        });
+
+        if let Ok(v) = res {
+          return Ok(v);
+        }
+      }
+      _ => {}
+    }
+  }
 }
 
 impl<'a, 'i> ToCssWithContext<'a, 'i> for StyleRule<'i> {