aboutsummaryrefslogtreecommitdiff
path: root/textwrap/src/indentation.rs
blob: 276ba1055345037b1ab83be823fc0b04a4b68a95 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
//! Functions related to adding and removing indentation from lines of
//! text.
//!
//! The functions here can be used to uniformly indent or dedent
//! (unindent) word wrapped lines of text.

/// Add prefix to each non-empty line.
///
/// ```
/// use textwrap::indent;
///
/// assert_eq!(indent("
/// Foo
/// Bar
/// ", "  "), "
///   Foo
///   Bar
/// ");
/// ```
///
/// Empty lines (lines consisting only of whitespace) are not indented
/// and the whitespace is replaced by a single newline (`\n`):
///
/// ```
/// use textwrap::indent;
///
/// assert_eq!(indent("
/// Foo
///
/// Bar
///   \t
/// Baz
/// ", "->"), "
/// ->Foo
///
/// ->Bar
///
/// ->Baz
/// ");
/// ```
///
/// Leading and trailing whitespace on non-empty lines is kept
/// unchanged:
///
/// ```
/// use textwrap::indent;
///
/// assert_eq!(indent(" \t  Foo   ", "->"), "-> \t  Foo   \n");
/// ```
pub fn indent(s: &str, prefix: &str) -> String {
    let mut result = String::new();
    for line in s.lines() {
        if line.chars().any(|c| !c.is_whitespace()) {
            result.push_str(prefix);
            result.push_str(line);
        }
        result.push('\n');
    }
    result
}

/// Removes common leading whitespace from each line.
///
/// This function will look at each non-empty line and determine the
/// maximum amount of whitespace that can be removed from all lines:
///
/// ```
/// use textwrap::dedent;
///
/// assert_eq!(dedent("
///     1st line
///       2nd line
///     3rd line
/// "), "
/// 1st line
///   2nd line
/// 3rd line
/// ");
/// ```
pub fn dedent(s: &str) -> String {
    let mut prefix = "";
    let mut lines = s.lines();

    // We first search for a non-empty line to find a prefix.
    for line in &mut lines {
        let mut whitespace_idx = line.len();
        for (idx, ch) in line.char_indices() {
            if !ch.is_whitespace() {
                whitespace_idx = idx;
                break;
            }
        }

        // Check if the line had anything but whitespace
        if whitespace_idx < line.len() {
            prefix = &line[..whitespace_idx];
            break;
        }
    }

    // We then continue looking through the remaining lines to
    // possibly shorten the prefix.
    for line in &mut lines {
        let mut whitespace_idx = line.len();
        for ((idx, a), b) in line.char_indices().zip(prefix.chars()) {
            if a != b {
                whitespace_idx = idx;
                break;
            }
        }

        // Check if the line had anything but whitespace and if we
        // have found a shorter prefix
        if whitespace_idx < line.len() && whitespace_idx < prefix.len() {
            prefix = &line[..whitespace_idx];
        }
    }

    // We now go over the lines a second time to build the result.
    let mut result = String::new();
    for line in s.lines() {
        if line.starts_with(&prefix) && line.chars().any(|c| !c.is_whitespace()) {
            let (_, tail) = line.split_at(prefix.len());
            result.push_str(tail);
        }
        result.push('\n');
    }

    if result.ends_with('\n') && !s.ends_with('\n') {
        let new_len = result.len() - 1;
        result.truncate(new_len);
    }

    result
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Add newlines. Ensures that the final line in the vector also
    /// has a newline.
    fn add_nl(lines: &[&str]) -> String {
        lines.join("\n") + "\n"
    }

    #[test]
    fn indent_empty() {
        assert_eq!(indent("\n", "  "), "\n");
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn indent_nonempty() {
        let x = vec!["  foo",
                     "bar",
                     "  baz"];
        let y = vec!["//  foo",
                     "//bar",
                     "//  baz"];
        assert_eq!(indent(&add_nl(&x), "//"), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn indent_empty_line() {
        let x = vec!["  foo",
                     "bar",
                     "",
                     "  baz"];
        let y = vec!["//  foo",
                     "//bar",
                     "",
                     "//  baz"];
        assert_eq!(indent(&add_nl(&x), "//"), add_nl(&y));
    }

    #[test]
    fn dedent_empty() {
        assert_eq!(dedent(""), "");
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_multi_line() {
        let x = vec!["    foo",
                     "  bar",
                     "    baz"];
        let y = vec!["  foo",
                     "bar",
                     "  baz"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_empty_line() {
        let x = vec!["    foo",
                     "  bar",
                     "   ",
                     "    baz"];
        let y = vec!["  foo",
                     "bar",
                     "",
                     "  baz"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_blank_line() {
        let x = vec!["      foo",
                     "",
                     "        bar",
                     "          foo",
                     "          bar",
                     "          baz"];
        let y = vec!["foo",
                     "",
                     "  bar",
                     "    foo",
                     "    bar",
                     "    baz"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_whitespace_line() {
        let x = vec!["      foo",
                     " ",
                     "        bar",
                     "          foo",
                     "          bar",
                     "          baz"];
        let y = vec!["foo",
                     "",
                     "  bar",
                     "    foo",
                     "    bar",
                     "    baz"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_mixed_whitespace() {
        let x = vec!["\tfoo",
                     "  bar"];
        let y = vec!["\tfoo",
                     "  bar"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_tabbed_whitespace() {
        let x = vec!["\t\tfoo",
                     "\t\t\tbar"];
        let y = vec!["foo",
                     "\tbar"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_mixed_tabbed_whitespace() {
        let x = vec!["\t  \tfoo",
                     "\t  \t\tbar"];
        let y = vec!["foo",
                     "\tbar"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_mixed_tabbed_whitespace2() {
        let x = vec!["\t  \tfoo",
                     "\t    \tbar"];
        let y = vec!["\tfoo",
                     "  \tbar"];
        assert_eq!(dedent(&add_nl(&x)), add_nl(&y));
    }

    #[test]
    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn dedent_preserve_no_terminating_newline() {
        let x = vec!["  foo",
                     "    bar"].join("\n");
        let y = vec!["foo",
                     "  bar"].join("\n");
        assert_eq!(dedent(&x), y);
    }
}