refactor lexer to use idiomatic borrowing

src/libsyntax/parse/lexer/mod.rs

@@ -321,33 +321,29 @@ impl<'a> StringReader<'a> {
         (pos - self.source_file.start_pos).to_usize()
     }
 
-    /// Calls `f` with a string slice of the source text spanning from `start`
-    /// up to but excluding `self.pos`, meaning the slice does not include
-    /// the character `self.ch`.
-    fn with_str_from<T, F>(&self, start: BytePos, f: F) -> T
-        where F: FnOnce(&str) -> T
+    /// Slice of the source text from `start` up to but excluding `self.pos`,
+    /// meaning the slice does not include the character `self.ch`.
+    fn str_from(&self, start: BytePos) -> &str
     {
-        self.with_str_from_to(start, self.pos, f)
+        self.str_from_to(start, self.pos)
     }
 
     /// Creates a Name from a given offset to the current offset.
     fn name_from(&self, start: BytePos) -> ast::Name {
         debug!("taking an ident from {:?} to {:?}", start, self.pos);
-        self.with_str_from(start, Symbol::intern)
+        Symbol::intern(self.str_from(start))
     }
 
     /// As name_from, with an explicit endpoint.
     fn name_from_to(&self, start: BytePos, end: BytePos) -> ast::Name {
         debug!("taking an ident from {:?} to {:?}", start, end);
-        self.with_str_from_to(start, end, Symbol::intern)
+        Symbol::intern(self.str_from_to(start, end))
     }
 
-    /// Calls `f` with a string slice of the source text spanning from `start`
-    /// up to but excluding `end`.
-    fn with_str_from_to<T, F>(&self, start: BytePos, end: BytePos, f: F) -> T
-        where F: FnOnce(&str) -> T
+    /// Slice of the source text spanning from `start` up to but excluding `end`.
+    fn str_from_to(&self, start: BytePos, end: BytePos) -> &str
     {
-        f(&self.src[self.src_index(start)..self.src_index(end)])
+        &self.src[self.src_index(start)..self.src_index(end)]
     }
 
     /// Converts CRLF to LF in the given string, raising an error on bare CR.
@@ -456,8 +452,8 @@ impl<'a> StringReader<'a> {
             self.bump();
         }
 
-        self.with_str_from(start, |string| {
-            if string == "_" {
+        match self.str_from(start) {
+            "_" => {
                 self.sess.span_diagnostic
                     .struct_span_warn(self.mk_sp(start, self.pos),
                                       "underscore literal suffix is not allowed")
@@ -468,10 +464,9 @@ impl<'a> StringReader<'a> {
                           <https://github.com/rust-lang/rust/issues/42326>")
                     .emit();
                 None
-            } else {
-                Some(Symbol::intern(string))
             }
-        })
+            name => Some(Symbol::intern(name))
+        }
     }
 
     /// PRECONDITION: self.ch is not whitespace
@@ -513,9 +508,7 @@ impl<'a> StringReader<'a> {
                     }
 
                     let kind = if doc_comment {
-                        self.with_str_from(start_bpos, |string| {
-                            token::DocComment(Symbol::intern(string))
-                        })
+                        token::DocComment(self.name_from(start_bpos))
                     } else {
                         token::Comment
                     };
@@ -615,23 +608,22 @@ impl<'a> StringReader<'a> {
             self.bump();
         }
 
-        self.with_str_from(start_bpos, |string| {
-            // but comments with only "*"s between two "/"s are not
-            let kind = if is_block_doc_comment(string) {
-                let string = if has_cr {
-                    self.translate_crlf(start_bpos,
-                                        string,
-                                        "bare CR not allowed in block doc-comment")
-                } else {
-                    string.into()
-                };
-                token::DocComment(Symbol::intern(&string[..]))
+        let string = self.str_from(start_bpos);
+        // but comments with only "*"s between two "/"s are not
+        let kind = if is_block_doc_comment(string) {
+            let string = if has_cr {
+                self.translate_crlf(start_bpos,
+                                    string,
+                                    "bare CR not allowed in block doc-comment")
             } else {
-                token::Comment
+                string.into()
             };
+            token::DocComment(Symbol::intern(&string[..]))
+        } else {
+            token::Comment
+        };
 
-            Some(Token::new(kind, self.mk_sp(start_bpos, self.pos)))
-        })
+        Some(Token::new(kind, self.mk_sp(start_bpos, self.pos)))
     }
 
     /// Scan through any digits (base `scan_radix`) or underscores,
@@ -838,20 +830,17 @@ impl<'a> StringReader<'a> {
                     self.bump();
                 }
 
-                return Ok(self.with_str_from(start, |string| {
-                    // FIXME: perform NFKC normalization here. (Issue #2253)
-                    let name = ast::Name::intern(string);
-
-                    if is_raw_ident {
-                        let span = self.mk_sp(raw_start, self.pos);
-                        if !name.can_be_raw() {
-                            self.err_span(span, &format!("`{}` cannot be a raw identifier", name));
-                        }
-                        self.sess.raw_identifier_spans.borrow_mut().push(span);
+                // FIXME: perform NFKC normalization here. (Issue #2253)
+                let name = self.name_from(start);
+                if is_raw_ident {
+                    let span = self.mk_sp(raw_start, self.pos);
+                    if !name.can_be_raw() {
+                        self.err_span(span, &format!("`{}` cannot be a raw identifier", name));
                     }
+                    self.sess.raw_identifier_spans.borrow_mut().push(span);
+                }
 
-                    token::Ident(name, is_raw_ident)
-                }));
+                return Ok(token::Ident(name, is_raw_ident));
             }
         }
 
@@ -1300,101 +1289,95 @@ impl<'a> StringReader<'a> {
     }
 
     fn validate_char_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            if let Err((off, err)) = unescape::unescape_char(lit) {
-                emit_unescape_error(
-                    &self.sess.span_diagnostic,
-                    lit,
-                    self.mk_sp(start_with_quote, self.pos),
-                    unescape::Mode::Char,
-                    0..off,
-                    err,
-                )
-            }
-        });
+        let lit = self.str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1));
+        if let Err((off, err)) = unescape::unescape_char(lit) {
+            emit_unescape_error(
+                &self.sess.span_diagnostic,
+                lit,
+                self.mk_sp(start_with_quote, self.pos),
+                unescape::Mode::Char,
+                0..off,
+                err,
+            )
+        }
     }
 
     fn validate_byte_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            if let Err((off, err)) = unescape::unescape_byte(lit) {
+        let lit = self.str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1));
+        if let Err((off, err)) = unescape::unescape_byte(lit) {
+            emit_unescape_error(
+                &self.sess.span_diagnostic,
+                lit,
+                self.mk_sp(start_with_quote, self.pos),
+                unescape::Mode::Byte,
+                0..off,
+                err,
+            )
+        }
+    }
+
+    fn validate_str_escape(&self, start_with_quote: BytePos) {
+        let lit = self.str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1));
+        unescape::unescape_str(lit, &mut |range, c| {
+            if let Err(err) = c {
                 emit_unescape_error(
                     &self.sess.span_diagnostic,
                     lit,
                     self.mk_sp(start_with_quote, self.pos),
-                    unescape::Mode::Byte,
-                    0..off,
+                    unescape::Mode::Str,
+                    range,
                     err,
                 )
             }
-        });
-    }
-
-    fn validate_str_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            unescape::unescape_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(start_with_quote, self.pos),
-                        unescape::Mode::Str,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+        })
     }
 
     fn validate_raw_str_escape(&self, content_start: BytePos, content_end: BytePos) {
-        self.with_str_from_to(content_start, content_end, |lit: &str| {
-            unescape::unescape_raw_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
-                        unescape::Mode::Str,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_raw_str(lit, &mut |range, c| {
+            if let Err(err) = c {
+                emit_unescape_error(
+                    &self.sess.span_diagnostic,
+                    lit,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::Str,
+                    range,
+                    err,
+                )
+            }
+        })
     }
 
     fn validate_raw_byte_str_escape(&self, content_start: BytePos, content_end: BytePos) {
-        self.with_str_from_to(content_start, content_end, |lit: &str| {
-            unescape::unescape_raw_byte_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
-                        unescape::Mode::ByteStr,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_raw_byte_str(lit, &mut |range, c| {
+            if let Err(err) = c {
+                emit_unescape_error(
+                    &self.sess.span_diagnostic,
+                    lit,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::ByteStr,
+                    range,
+                    err,
+                )
+            }
+        })
     }
 
     fn validate_byte_str_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            unescape::unescape_byte_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(start_with_quote, self.pos),
-                        unescape::Mode::ByteStr,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+        let lit = self.str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1));
+        unescape::unescape_byte_str(lit, &mut |range, c| {
+            if let Err(err) = c {
+                emit_unescape_error(
+                    &self.sess.span_diagnostic,
+                    lit,
+                    self.mk_sp(start_with_quote, self.pos),
+                    unescape::Mode::ByteStr,
+                    range,
+                    err,
+                )
+            }
+        })
     }
 }