1 files changed, 201 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/string_lexing/parser.rs b/crates/ra_syntax/src/string_lexing/parser.rs
new file mode 100644
index 000000000..4a6d5bc93
--- /dev/null
+++ b/crates/ra_syntax/src/string_lexing/parser.rs
@@ -0,0 +1,201 @@
+use rowan::{TextRange, TextUnit};
+
+use self::CharComponentKind::*;
+
+pub struct Parser<'a> {
+    pub(super) src: &'a str,
+    pub(super) pos: usize,
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(src: &'a str) -> Parser<'a> {
+        Parser { src, pos: 0 }
+    }
+
+    // Utility methods
+
+    pub fn peek(&self) -> Option<char> {
+        if self.pos == self.src.len() {
+            return None;
+        }
+
+        self.src[self.pos..].chars().next()
+    }
+
+    pub fn advance(&mut self) -> char {
+        let next = self
+            .peek()
+            .expect("cannot advance if end of input is reached");
+        self.pos += next.len_utf8();
+        next
+    }
+
+    pub fn skip_whitespace(&mut self) {
+        while self.peek().map(|c| c.is_whitespace()) == Some(true) {
+            self.advance();
+        }
+    }
+
+    pub fn get_pos(&self) -> TextUnit {
+        (self.pos as u32).into()
+    }
+
+    // Char parsing methods
+
+    fn parse_unicode_escape(&mut self, start: TextUnit) -> CharComponent {
+        match self.peek() {
+            Some('{') => {
+                self.advance();
+
+                // Parse anything until we reach `}`
+                while let Some(next) = self.peek() {
+                    self.advance();
+                    if next == '}' {
+                        break;
+                    }
+                }
+
+                let end = self.get_pos();
+                CharComponent::new(TextRange::from_to(start, end), UnicodeEscape)
+            }
+            Some(_) | None => {
+                let end = self.get_pos();
+                CharComponent::new(TextRange::from_to(start, end), UnicodeEscape)
+            }
+        }
+    }
+
+    fn parse_ascii_code_escape(&mut self, start: TextUnit) -> CharComponent {
+        let code_start = self.get_pos();
+        while let Some(next) = self.peek() {
+            if next == '\'' || (self.get_pos() - code_start == 2.into()) {
+                break;
+            }
+
+            self.advance();
+        }
+
+        let end = self.get_pos();
+        CharComponent::new(TextRange::from_to(start, end), AsciiCodeEscape)
+    }
+
+    fn parse_escape(&mut self, start: TextUnit) -> CharComponent {
+        if self.peek().is_none() {
+            return CharComponent::new(TextRange::from_to(start, start), AsciiEscape);
+        }
+
+        let next = self.advance();
+        let end = self.get_pos();
+        let range = TextRange::from_to(start, end);
+        match next {
+            'x' => self.parse_ascii_code_escape(start),
+            'u' => self.parse_unicode_escape(start),
+            _ => CharComponent::new(range, AsciiEscape),
+        }
+    }
+
+    pub fn parse_char_component(&mut self) -> Option<CharComponent> {
+        let next = self.peek()?;
+
+        // Ignore character close
+        if next == '\'' {
+            return None;
+        }
+
+        let start = self.get_pos();
+        self.advance();
+
+        if next == '\\' {
+            Some(self.parse_escape(start))
+        } else {
+            let end = self.get_pos();
+            Some(CharComponent::new(
+                TextRange::from_to(start, end),
+                CodePoint,
+            ))
+        }
+    }
+
+    pub fn parse_ignore_newline(&mut self, start: TextUnit) -> Option<StringComponent> {
+        // In string literals, when a `\` occurs immediately before the newline, the `\`,
+        // the newline, and all whitespace at the beginning of the next line are ignored
+        match self.peek() {
+            Some('\n') | Some('\r') => {
+                self.skip_whitespace();
+                Some(StringComponent::new(
+                    TextRange::from_to(start, self.get_pos()),
+                    StringComponentKind::IgnoreNewline,
+                ))
+            }
+            _ => None,
+        }
+    }
+
+    pub fn parse_string_component(&mut self) -> Option<StringComponent> {
+        let next = self.peek()?;
+
+        // Ignore string close
+        if next == '"' {
+            return None;
+        }
+
+        let start = self.get_pos();
+        self.advance();
+
+        if next == '\\' {
+            // Strings can use `\` to ignore newlines, so we first try to parse one of those
+            // before falling back to parsing char escapes
+            self.parse_ignore_newline(start).or_else(|| {
+                let char_component = self.parse_escape(start);
+                Some(StringComponent::new(
+                    char_component.range,
+                    StringComponentKind::Char(char_component.kind),
+                ))
+            })
+        } else {
+            let end = self.get_pos();
+            Some(StringComponent::new(
+                TextRange::from_to(start, end),
+                StringComponentKind::Char(CodePoint),
+            ))
+        }
+    }
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub struct StringComponent {
+    pub range: TextRange,
+    pub kind: StringComponentKind,
+}
+
+impl StringComponent {
+    fn new(range: TextRange, kind: StringComponentKind) -> StringComponent {
+        StringComponent { range, kind }
+    }
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub enum StringComponentKind {
+    IgnoreNewline,
+    Char(CharComponentKind),
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub struct CharComponent {
+    pub range: TextRange,
+    pub kind: CharComponentKind,
+}
+
+impl CharComponent {
+    fn new(range: TextRange, kind: CharComponentKind) -> CharComponent {
+        CharComponent { range, kind }
+    }
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub enum CharComponentKind {
+    CodePoint,
+    AsciiEscape,
+    AsciiCodeEscape,
+    UnicodeEscape,
+}