]> git.lizzy.rs Git - rust.git/blobdiff - src/string.rs
Merge commit 'c4416f20dcaec5d93077f72470e83e150fb923b1' into sync-rustfmt
[rust.git] / src / string.rs
index 39eaf57d72e9487836d0f63c5a758b1b67ad7bc0..78b72a50cb2f96250ec94b1c86579d1246798424 100644 (file)
@@ -1,36 +1,34 @@
-// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
 // Format string literals.
 
 use regex::Regex;
+use unicode_categories::UnicodeCategories;
 use unicode_segmentation::UnicodeSegmentation;
 
-use config::Config;
-use shape::Shape;
-use utils::wrap_str;
+use crate::config::Config;
+use crate::shape::Shape;
+use crate::utils::{unicode_str_width, wrap_str};
 
 const MIN_STRING: usize = 10;
 
-pub struct StringFormat<'a> {
-    pub opener: &'a str,
-    pub closer: &'a str,
-    pub line_start: &'a str,
-    pub line_end: &'a str,
-    pub shape: Shape,
-    pub trim_end: bool,
-    pub config: &'a Config,
+/// Describes the layout of a piece of text.
+pub(crate) struct StringFormat<'a> {
+    /// The opening sequence of characters for the piece of text
+    pub(crate) opener: &'a str,
+    /// The closing sequence of characters for the piece of text
+    pub(crate) closer: &'a str,
+    /// The opening sequence of characters for a line
+    pub(crate) line_start: &'a str,
+    /// The closing sequence of characters for a line
+    pub(crate) line_end: &'a str,
+    /// The allocated box to fit the text into
+    pub(crate) shape: Shape,
+    /// Trim trailing whitespaces
+    pub(crate) trim_end: bool,
+    pub(crate) config: &'a Config,
 }
 
 impl<'a> StringFormat<'a> {
-    pub fn new(shape: Shape, config: &'a Config) -> StringFormat<'a> {
+    pub(crate) fn new(shape: Shape, config: &'a Config) -> StringFormat<'a> {
         StringFormat {
             opener: "\"",
             closer: "\"",
@@ -41,21 +39,44 @@ pub fn new(shape: Shape, config: &'a Config) -> StringFormat<'a> {
             config,
         }
     }
+
+    /// Returns the maximum number of graphemes that is possible on a line while taking the
+    /// indentation into account.
+    ///
+    /// If we cannot put at least a single character per line, the rewrite won't succeed.
+    fn max_width_with_indent(&self) -> Option<usize> {
+        Some(
+            self.shape
+                .width
+                .checked_sub(self.opener.len() + self.line_end.len() + 1)?
+                + 1,
+        )
+    }
+
+    /// Like max_width_with_indent but the indentation is not subtracted.
+    /// This allows to fit more graphemes from the string on a line when
+    /// SnippetState::EndWithLineFeed.
+    fn max_width_without_indent(&self) -> Option<usize> {
+        self.config.max_width().checked_sub(self.line_end.len())
+    }
 }
 
-// FIXME: simplify this!
-pub fn rewrite_string<'a>(
+pub(crate) fn rewrite_string<'a>(
     orig: &str,
     fmt: &StringFormat<'a>,
-    max_width: Option<usize>,
+    newline_max_chars: usize,
 ) -> Option<String> {
+    let max_width_with_indent = fmt.max_width_with_indent()?;
+    let max_width_without_indent = fmt.max_width_without_indent()?;
+    let indent_with_newline = fmt.shape.indent.to_string_with_newline(fmt.config);
+    let indent_without_newline = fmt.shape.indent.to_string(fmt.config);
+
     // Strip line breaks.
-    let re = Regex::new(r"([^\\](\\\\)*)\\[\n\r][[:space:]]*").unwrap();
-    let stripped_str = re.replace_all(orig, "$1");
+    // With this regex applied, all remaining whitespaces are significant
+    let strip_line_breaks_re = Regex::new(r"([^\\](\\\\)*)\\[\n\r][[:space:]]*").unwrap();
+    let stripped_str = strip_line_breaks_re.replace_all(orig, "$1");
 
     let graphemes = UnicodeSegmentation::graphemes(&*stripped_str, false).collect::<Vec<&str>>();
-    let shape = fmt.shape;
-    let indent = shape.indent.to_string_with_newline(fmt.config);
 
     // `cur_start` is the position in `orig` of the start of the current line.
     let mut cur_start = 0;
@@ -67,107 +88,638 @@ pub fn rewrite_string<'a>(
     );
     result.push_str(fmt.opener);
 
-    let ender_length = fmt.line_end.len();
-    // If we cannot put at least a single character per line, the rewrite won't
-    // succeed.
-    let mut max_chars = shape
-        .width
-        .checked_sub(fmt.opener.len() + ender_length + 1)?
-        + 1;
-
-    // Snip a line at a time from `orig` until it is used up. Push the snippet
+    // Snip a line at a time from `stripped_str` until it is used up. Push the snippet
     // onto result.
-    'outer: loop {
-        // `cur_end` will be where we break the line, as an offset into `orig`.
-        // Initialised to the maximum it could be (which may be beyond `orig`).
-        let mut cur_end = cur_start + max_chars;
-
-        // We can fit the rest of the string on this line, so we're done.
-        if cur_end >= graphemes.len() {
-            let line = &graphemes[cur_start..].join("");
-            result.push_str(line);
-            break 'outer;
+    let mut cur_max_width = max_width_with_indent;
+    let is_bareline_ok = fmt.line_start.is_empty() || is_whitespace(fmt.line_start);
+    loop {
+        // All the input starting at cur_start fits on the current line
+        if graphemes_width(&graphemes[cur_start..]) <= cur_max_width {
+            for (i, grapheme) in graphemes[cur_start..].iter().enumerate() {
+                if is_new_line(grapheme) {
+                    // take care of blank lines
+                    result = trim_end_but_line_feed(fmt.trim_end, result);
+                    result.push('\n');
+                    if !is_bareline_ok && cur_start + i + 1 < graphemes.len() {
+                        result.push_str(&indent_without_newline);
+                        result.push_str(fmt.line_start);
+                    }
+                } else {
+                    result.push_str(grapheme);
+                }
+            }
+            result = trim_end_but_line_feed(fmt.trim_end, result);
+            break;
+        }
+
+        // The input starting at cur_start needs to be broken
+        match break_string(
+            cur_max_width,
+            fmt.trim_end,
+            fmt.line_end,
+            &graphemes[cur_start..],
+        ) {
+            SnippetState::LineEnd(line, len) => {
+                result.push_str(&line);
+                result.push_str(fmt.line_end);
+                result.push_str(&indent_with_newline);
+                result.push_str(fmt.line_start);
+                cur_max_width = newline_max_chars;
+                cur_start += len;
+            }
+            SnippetState::EndWithLineFeed(line, len) => {
+                if line == "\n" && fmt.trim_end {
+                    result = result.trim_end().to_string();
+                }
+                result.push_str(&line);
+                if is_bareline_ok {
+                    // the next line can benefit from the full width
+                    cur_max_width = max_width_without_indent;
+                } else {
+                    result.push_str(&indent_without_newline);
+                    result.push_str(fmt.line_start);
+                    cur_max_width = max_width_with_indent;
+                }
+                cur_start += len;
+            }
+            SnippetState::EndOfInput(line) => {
+                result.push_str(&line);
+                break;
+            }
+        }
+    }
+
+    result.push_str(fmt.closer);
+    wrap_str(result, fmt.config.max_width(), fmt.shape)
+}
+
+/// Returns the index to the end of the URL if the split at index of the given string includes a
+/// URL or alike. Otherwise, returns `None`.
+fn detect_url(s: &[&str], index: usize) -> Option<usize> {
+    let start = match s[..=index].iter().rposition(|g| is_whitespace(g)) {
+        Some(pos) => pos + 1,
+        None => 0,
+    };
+    // 8 = minimum length for a string to contain a URL
+    if s.len() < start + 8 {
+        return None;
+    }
+    let split = s[start..].concat();
+    if split.contains("https://")
+        || split.contains("http://")
+        || split.contains("ftp://")
+        || split.contains("file://")
+    {
+        match s[index..].iter().position(|g| is_whitespace(g)) {
+            Some(pos) => Some(index + pos - 1),
+            None => Some(s.len() - 1),
         }
+    } else {
+        None
+    }
+}
+
+/// Trims whitespaces to the right except for the line feed character.
+fn trim_end_but_line_feed(trim_end: bool, result: String) -> String {
+    let whitespace_except_line_feed = |c: char| c.is_whitespace() && c != '\n';
+    if trim_end && result.ends_with(whitespace_except_line_feed) {
+        result
+            .trim_end_matches(whitespace_except_line_feed)
+            .to_string()
+    } else {
+        result
+    }
+}
+
+/// Result of breaking a string so it fits in a line and the state it ended in.
+/// The state informs about what to do with the snippet and how to continue the breaking process.
+#[derive(Debug, PartialEq)]
+enum SnippetState {
+    /// The input could not be broken and so rewriting the string is finished.
+    EndOfInput(String),
+    /// The input could be broken and the returned snippet should be ended with a
+    /// `[StringFormat::line_end]`. The next snippet needs to be indented.
+    ///
+    /// The returned string is the line to print out and the number is the length that got read in
+    /// the text being rewritten. That length may be greater than the returned string if trailing
+    /// whitespaces got trimmed.
+    LineEnd(String, usize),
+    /// The input could be broken but a newline is present that cannot be trimmed. The next snippet
+    /// to be rewritten *could* use more width than what is specified by the given shape. For
+    /// example with a multiline string, the next snippet does not need to be indented, allowing
+    /// more characters to be fit within a line.
+    ///
+    /// The returned string is the line to print out and the number is the length that got read in
+    /// the text being rewritten.
+    EndWithLineFeed(String, usize),
+}
+
+fn not_whitespace_except_line_feed(g: &str) -> bool {
+    is_new_line(g) || !is_whitespace(g)
+}
 
-        // Push cur_end left until we reach whitespace (or the line is too small).
-        while !is_whitespace(graphemes[cur_end - 1]) {
-            cur_end -= 1;
-            if cur_end < cur_start + MIN_STRING {
-                // We couldn't find whitespace before the string got too small.
-                // So start again at the max length and look for punctuation.
-                cur_end = cur_start + max_chars;
-                while !is_punctuation(graphemes[cur_end - 1]) {
-                    cur_end -= 1;
-
-                    // If we can't break at whitespace or punctuation, grow the string instead.
-                    if cur_end < cur_start + MIN_STRING {
-                        cur_end = cur_start + max_chars;
-                        while !(is_punctuation(graphemes[cur_end - 1])
-                            || is_whitespace(graphemes[cur_end - 1]))
-                        {
-                            cur_end += 1;
-                            if cur_end == graphemes.len() {
-                                let line = &graphemes[cur_start..].join("");
-                                result.push_str(line);
-                                break 'outer;
-                            }
-                        }
-                        break;
+/// Break the input string at a boundary character around the offset `max_width`. A boundary
+/// character is either a punctuation or a whitespace.
+/// FIXME(issue#3281): We must follow UAX#14 algorithm instead of this.
+fn break_string(max_width: usize, trim_end: bool, line_end: &str, input: &[&str]) -> SnippetState {
+    let break_at = |index /* grapheme at index is included */| {
+        // Take in any whitespaces to the left/right of `input[index]` while
+        // preserving line feeds
+        let index_minus_ws = input[0..=index]
+            .iter()
+            .rposition(|grapheme| not_whitespace_except_line_feed(grapheme))
+            .unwrap_or(index);
+        // Take into account newlines occurring in input[0..=index], i.e., the possible next new
+        // line. If there is one, then text after it could be rewritten in a way that the available
+        // space is fully used.
+        for (i, grapheme) in input[0..=index].iter().enumerate() {
+            if is_new_line(grapheme) {
+                if i <= index_minus_ws {
+                    let mut line = &input[0..i].concat()[..];
+                    if trim_end {
+                        line = line.trim_end();
                     }
+                    return SnippetState::EndWithLineFeed(format!("{}\n", line), i + 1);
                 }
                 break;
             }
         }
-        // Make sure there is no whitespace to the right of the break.
-        while cur_end < stripped_str.len() && is_whitespace(graphemes[cur_end]) {
-            cur_end += 1;
+
+        let mut index_plus_ws = index;
+        for (i, grapheme) in input[index + 1..].iter().enumerate() {
+            if !trim_end && is_new_line(grapheme) {
+                return SnippetState::EndWithLineFeed(
+                    input[0..=index + 1 + i].concat(),
+                    index + 2 + i,
+                );
+            } else if not_whitespace_except_line_feed(grapheme) {
+                index_plus_ws = index + i;
+                break;
+            }
         }
 
-        // Make the current line and add it on to result.
-        let raw_line = graphemes[cur_start..cur_end].join("");
-        let line = if fmt.trim_end {
-            raw_line.trim()
+        if trim_end {
+            SnippetState::LineEnd(input[0..=index_minus_ws].concat(), index_plus_ws + 1)
         } else {
-            raw_line.as_str()
-        };
+            SnippetState::LineEnd(input[0..=index_plus_ws].concat(), index_plus_ws + 1)
+        }
+    };
 
-        result.push_str(line);
-        result.push_str(fmt.line_end);
-        result.push_str(&indent);
-        result.push_str(fmt.line_start);
+    // find a first index where the unicode width of input[0..x] become > max_width
+    let max_width_index_in_input = {
+        let mut cur_width = 0;
+        let mut cur_index = 0;
+        for (i, grapheme) in input.iter().enumerate() {
+            cur_width += unicode_str_width(grapheme);
+            cur_index = i;
+            if cur_width > max_width {
+                break;
+            }
+        }
+        cur_index
+    };
+    if max_width_index_in_input == 0 {
+        return SnippetState::EndOfInput(input.concat());
+    }
 
-        // The next line starts where the current line ends.
-        cur_start = cur_end;
+    // Find the position in input for breaking the string
+    if line_end.is_empty()
+        && trim_end
+        && !is_whitespace(input[max_width_index_in_input - 1])
+        && is_whitespace(input[max_width_index_in_input])
+    {
+        // At a breaking point already
+        // The line won't invalidate the rewriting because:
+        // - no extra space needed for the line_end character
+        // - extra whitespaces to the right can be trimmed
+        return break_at(max_width_index_in_input - 1);
+    }
+    if let Some(url_index_end) = detect_url(input, max_width_index_in_input) {
+        let index_plus_ws = url_index_end
+            + input[url_index_end..]
+                .iter()
+                .skip(1)
+                .position(|grapheme| not_whitespace_except_line_feed(grapheme))
+                .unwrap_or(0);
+        return if trim_end {
+            SnippetState::LineEnd(input[..=url_index_end].concat(), index_plus_ws + 1)
+        } else {
+            SnippetState::LineEnd(input[..=index_plus_ws].concat(), index_plus_ws + 1)
+        };
+    }
 
-        if let Some(new_max_chars) = max_width {
-            max_chars = new_max_chars.checked_sub(fmt.opener.len() + ender_length + 1)? + 1;
-        }
+    match input[0..max_width_index_in_input]
+        .iter()
+        .rposition(|grapheme| is_whitespace(grapheme))
+    {
+        // Found a whitespace and what is on its left side is big enough.
+        Some(index) if index >= MIN_STRING => break_at(index),
+        // No whitespace found, try looking for a punctuation instead
+        _ => match (0..max_width_index_in_input)
+            .rev()
+            .skip_while(|pos| !is_valid_linebreak(input, *pos))
+            .next()
+        {
+            // Found a punctuation and what is on its left side is big enough.
+            Some(index) if index >= MIN_STRING => break_at(index),
+            // Either no boundary character was found to the left of `input[max_chars]`, or the line
+            // got too small. We try searching for a boundary character to the right.
+            _ => match (max_width_index_in_input..input.len())
+                .skip_while(|pos| !is_valid_linebreak(input, *pos))
+                .next()
+            {
+                // A boundary was found after the line limit
+                Some(index) => break_at(index),
+                // No boundary to the right, the input cannot be broken
+                None => SnippetState::EndOfInput(input.concat()),
+            },
+        },
     }
+}
 
-    result.push_str(fmt.closer);
-    wrap_str(result, fmt.config.max_width(), fmt.shape)
+fn is_valid_linebreak(input: &[&str], pos: usize) -> bool {
+    let is_whitespace = is_whitespace(input[pos]);
+    if is_whitespace {
+        return true;
+    }
+    let is_punctuation = is_punctuation(input[pos]);
+    if is_punctuation && !is_part_of_type(input, pos) {
+        return true;
+    }
+    false
+}
+
+fn is_part_of_type(input: &[&str], pos: usize) -> bool {
+    input.get(pos..=pos + 1) == Some(&[":", ":"])
+        || input.get(pos.saturating_sub(1)..=pos) == Some(&[":", ":"])
+}
+
+fn is_new_line(grapheme: &str) -> bool {
+    let bytes = grapheme.as_bytes();
+    bytes.starts_with(b"\n") || bytes.starts_with(b"\r\n")
 }
 
 fn is_whitespace(grapheme: &str) -> bool {
-    grapheme.chars().all(|c| c.is_whitespace())
+    grapheme.chars().all(char::is_whitespace)
 }
 
 fn is_punctuation(grapheme: &str) -> bool {
-    match grapheme.as_bytes()[0] {
-        b':' | b',' | b';' | b'.' => true,
-        _ => false,
-    }
+    grapheme
+        .chars()
+        .all(UnicodeCategories::is_punctuation_other)
+}
+
+fn graphemes_width(graphemes: &[&str]) -> usize {
+    graphemes.iter().map(|s| unicode_str_width(s)).sum()
 }
 
 #[cfg(test)]
 mod test {
-    use super::{rewrite_string, StringFormat};
-    use shape::{Indent, Shape};
+    use super::{break_string, detect_url, rewrite_string, SnippetState, StringFormat};
+    use crate::config::Config;
+    use crate::shape::{Indent, Shape};
+    use unicode_segmentation::UnicodeSegmentation;
 
     #[test]
     fn issue343() {
         let config = Default::default();
         let fmt = StringFormat::new(Shape::legacy(2, Indent::empty()), &config);
-        rewrite_string("eq_", &fmt, None);
+        rewrite_string("eq_", &fmt, 2);
+    }
+
+    #[test]
+    fn line_break_at_valid_points_test() {
+        let string = "[TheName](Dont::break::my::type::That::would::be::very::nice) break here";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::LineEnd(
+                "[TheName](Dont::break::my::type::That::would::be::very::nice) ".to_string(),
+                62
+            )
+        );
+    }
+
+    #[test]
+    fn should_break_on_whitespace() {
+        let string = "Placerat felis. Mauris porta ante sagittis purus.";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::LineEnd("Placerat felis. ".to_string(), 16)
+        );
+        assert_eq!(
+            break_string(20, true, "", &graphemes[..]),
+            SnippetState::LineEnd("Placerat felis.".to_string(), 16)
+        );
+    }
+
+    #[test]
+    fn should_break_on_punctuation() {
+        let string = "Placerat_felis._Mauris_porta_ante_sagittis_purus.";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::LineEnd("Placerat_felis.".to_string(), 15)
+        );
+    }
+
+    #[test]
+    fn should_break_forward() {
+        let string = "Venenatis_tellus_vel_tellus. Aliquam aliquam dolor at justo.";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::LineEnd("Venenatis_tellus_vel_tellus. ".to_string(), 29)
+        );
+        assert_eq!(
+            break_string(20, true, "", &graphemes[..]),
+            SnippetState::LineEnd("Venenatis_tellus_vel_tellus.".to_string(), 29)
+        );
+    }
+
+    #[test]
+    fn nothing_to_break() {
+        let string = "Venenatis_tellus_vel_tellus";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::EndOfInput("Venenatis_tellus_vel_tellus".to_string())
+        );
+    }
+
+    #[test]
+    fn significant_whitespaces() {
+        let string = "Neque in sem.      \n      Pellentesque tellus augue.";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(15, false, "", &graphemes[..]),
+            SnippetState::EndWithLineFeed("Neque in sem.      \n".to_string(), 20)
+        );
+        assert_eq!(
+            break_string(25, false, "", &graphemes[..]),
+            SnippetState::EndWithLineFeed("Neque in sem.      \n".to_string(), 20)
+        );
+
+        assert_eq!(
+            break_string(15, true, "", &graphemes[..]),
+            SnippetState::LineEnd("Neque in sem.".to_string(), 19)
+        );
+        assert_eq!(
+            break_string(25, true, "", &graphemes[..]),
+            SnippetState::EndWithLineFeed("Neque in sem.\n".to_string(), 20)
+        );
+    }
+
+    #[test]
+    fn big_whitespace() {
+        let string = "Neque in sem.            Pellentesque tellus augue.";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(20, false, "", &graphemes[..]),
+            SnippetState::LineEnd("Neque in sem.            ".to_string(), 25)
+        );
+        assert_eq!(
+            break_string(20, true, "", &graphemes[..]),
+            SnippetState::LineEnd("Neque in sem.".to_string(), 25)
+        );
+    }
+
+    #[test]
+    fn newline_in_candidate_line() {
+        let string = "Nulla\nconsequat erat at massa. Vivamus id mi.";
+
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(
+            break_string(25, false, "", &graphemes[..]),
+            SnippetState::EndWithLineFeed("Nulla\n".to_string(), 6)
+        );
+        assert_eq!(
+            break_string(25, true, "", &graphemes[..]),
+            SnippetState::EndWithLineFeed("Nulla\n".to_string(), 6)
+        );
+
+        let mut config: Config = Default::default();
+        config.set().max_width(27);
+        let fmt = StringFormat::new(Shape::legacy(25, Indent::empty()), &config);
+        let rewritten_string = rewrite_string(string, &fmt, 27);
+        assert_eq!(
+            rewritten_string,
+            Some("\"Nulla\nconsequat erat at massa. \\\n Vivamus id mi.\"".to_string())
+        );
+    }
+
+    #[test]
+    fn last_line_fit_with_trailing_whitespaces() {
+        let string = "Vivamus id mi.  ";
+        let config: Config = Default::default();
+        let mut fmt = StringFormat::new(Shape::legacy(25, Indent::empty()), &config);
+
+        fmt.trim_end = true;
+        let rewritten_string = rewrite_string(string, &fmt, 25);
+        assert_eq!(rewritten_string, Some("\"Vivamus id mi.\"".to_string()));
+
+        fmt.trim_end = false; // default value of trim_end
+        let rewritten_string = rewrite_string(string, &fmt, 25);
+        assert_eq!(rewritten_string, Some("\"Vivamus id mi.  \"".to_string()));
+    }
+
+    #[test]
+    fn last_line_fit_with_newline() {
+        let string = "Vivamus id mi.\nVivamus id mi.";
+        let config: Config = Default::default();
+        let fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "",
+            shape: Shape::legacy(100, Indent::from_width(&config, 4)),
+            trim_end: true,
+            config: &config,
+        };
+
+        let rewritten_string = rewrite_string(string, &fmt, 100);
+        assert_eq!(
+            rewritten_string,
+            Some("Vivamus id mi.\n    // Vivamus id mi.".to_string())
+        );
+    }
+
+    #[test]
+    fn overflow_in_non_string_content() {
+        let comment = "Aenean metus.\nVestibulum ac lacus. Vivamus porttitor";
+        let config: Config = Default::default();
+        let fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "",
+            shape: Shape::legacy(30, Indent::from_width(&config, 8)),
+            trim_end: true,
+            config: &config,
+        };
+
+        assert_eq!(
+            rewrite_string(comment, &fmt, 30),
+            Some(
+                "Aenean metus.\n        // Vestibulum ac lacus. Vivamus\n        // porttitor"
+                    .to_string()
+            )
+        );
+    }
+
+    #[test]
+    fn overflow_in_non_string_content_with_line_end() {
+        let comment = "Aenean metus.\nVestibulum ac lacus. Vivamus porttitor";
+        let config: Config = Default::default();
+        let fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "@",
+            shape: Shape::legacy(30, Indent::from_width(&config, 8)),
+            trim_end: true,
+            config: &config,
+        };
+
+        assert_eq!(
+            rewrite_string(comment, &fmt, 30),
+            Some(
+                "Aenean metus.\n        // Vestibulum ac lacus. Vivamus@\n        // porttitor"
+                    .to_string()
+            )
+        );
+    }
+
+    #[test]
+    fn blank_line_with_non_empty_line_start() {
+        let config: Config = Default::default();
+        let mut fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "",
+            shape: Shape::legacy(30, Indent::from_width(&config, 4)),
+            trim_end: true,
+            config: &config,
+        };
+
+        let comment = "Aenean metus. Vestibulum\n\nac lacus. Vivamus porttitor";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 30),
+            Some(
+                "Aenean metus. Vestibulum\n    //\n    // ac lacus. Vivamus porttitor".to_string()
+            )
+        );
+
+        fmt.shape = Shape::legacy(15, Indent::from_width(&config, 4));
+        let comment = "Aenean\n\nmetus. Vestibulum ac lacus. Vivamus porttitor";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 15),
+            Some(
+                r#"Aenean
+    //
+    // metus. Vestibulum
+    // ac lacus. Vivamus
+    // porttitor"#
+                    .to_string()
+            )
+        );
+    }
+
+    #[test]
+    fn retain_blank_lines() {
+        let config: Config = Default::default();
+        let fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "",
+            shape: Shape::legacy(20, Indent::from_width(&config, 4)),
+            trim_end: true,
+            config: &config,
+        };
+
+        let comment = "Aenean\n\nmetus. Vestibulum ac lacus.\n\n";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 20),
+            Some(
+                "Aenean\n    //\n    // metus. Vestibulum ac\n    // lacus.\n    //\n".to_string()
+            )
+        );
+
+        let comment = "Aenean\n\nmetus. Vestibulum ac lacus.\n";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 20),
+            Some("Aenean\n    //\n    // metus. Vestibulum ac\n    // lacus.\n".to_string())
+        );
+
+        let comment = "Aenean\n        \nmetus. Vestibulum ac lacus.";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 20),
+            Some("Aenean\n    //\n    // metus. Vestibulum ac\n    // lacus.".to_string())
+        );
+    }
+
+    #[test]
+    fn boundary_on_edge() {
+        let config: Config = Default::default();
+        let mut fmt = StringFormat {
+            opener: "",
+            closer: "",
+            line_start: "// ",
+            line_end: "",
+            shape: Shape::legacy(13, Indent::from_width(&config, 4)),
+            trim_end: true,
+            config: &config,
+        };
+
+        let comment = "Aenean metus. Vestibulum ac lacus.";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 13),
+            Some("Aenean metus.\n    // Vestibulum ac\n    // lacus.".to_string())
+        );
+
+        fmt.trim_end = false;
+        let comment = "Vestibulum ac lacus.";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 13),
+            Some("Vestibulum \n    // ac lacus.".to_string())
+        );
+
+        fmt.trim_end = true;
+        fmt.line_end = "\\";
+        let comment = "Vestibulum ac lacus.";
+        assert_eq!(
+            rewrite_string(comment, &fmt, 13),
+            Some("Vestibulum\\\n    // ac lacus.".to_string())
+        );
+    }
+
+    #[test]
+    fn detect_urls() {
+        let string = "aaa http://example.org something";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 8), Some(21));
+
+        let string = "https://example.org something";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 0), Some(18));
+
+        let string = "aaa ftp://example.org something";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 8), Some(20));
+
+        let string = "aaa file://example.org something";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 8), Some(21));
+
+        let string = "aaa http not an url";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 6), None);
+
+        let string = "aaa file://example.org";
+        let graphemes = UnicodeSegmentation::graphemes(&*string, false).collect::<Vec<&str>>();
+        assert_eq!(detect_url(&graphemes, 8), Some(21));
     }
 }