conf 0.4.5

A derive-based config parser for CLI args, env, and structured config files
Documentation 
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

use clap_lex::RawArgs;
use std::ffi::OsString;

/// In some cases, you may want to grab a config file path from CLI args before doing the
/// main parse, so that you can load the config file content and pass it to conf::conf_builder(),
/// if the config file path was present.
///
/// This helper function uses `clap_lex` to do that, which is already indirectly a dependency of
/// `conf` anyways. It is only meant to be used for a one-off like this that is needed before the
/// main parse.
///
/// See `examples/serde/basic.rs` for example usage.
///
/// Limitations:
///
/// * Only returns the first example that it finds on the command line. Don't use this with a multi
///   option, only with a parameter.
/// * No error reporting. If the parameter is found but has no argument, we just return `None`. That
///   is expected to be caught in the `Conf::parse` step.
/// * No auto-generated docs.
///
/// If you use this, you should add a dummy parameter of the same name to your top-level config
/// struct, even if it is not used later in the program, so that you don't get an "unexpected
/// argument" error during the main parse, and so that this parameter will appear in the `--help`.
pub fn find_parameter(
    name: &str,
    args_os: impl IntoIterator<Item: Into<OsString>>,
) -> Option<OsString> {
    let raw = RawArgs::new(args_os);
    let mut cursor = raw.cursor();
    raw.next(&mut cursor); // Skip the bin

    while let Some(arg) = raw.next(&mut cursor) {
        if arg.is_escape() {
            return None;
        } else if let Some((maybe_flag, maybe_value)) = arg.to_long() {
            let Ok(flag) = maybe_flag else {
                continue;
            };

            if flag != name {
                continue;
            }

            // We found what we are searching for, now the two possibilities are
            // --flag=value
            // and
            // --flag value
            if let Some(value) = maybe_value {
                return Some(value.to_owned());
            } else {
                // Note: If there is no next value, it should be thought of as an error,
                // but we just return None, and let the main parse do the error reporting.
                return raw.next_os(&mut cursor).map(|os_str| os_str.to_owned());
            }
        }
    }

    None
}

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

    #[test]
    fn test_find_parameter() {
        assert_eq!(None, find_parameter("foo", ["."]));

        assert_eq!(
            "x",
            find_parameter("foo", [".", "--foo=x"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(None, find_parameter("fo", [".", "--foo=x"]));
        assert_eq!(None, find_parameter("fooo", [".", "--foo=x"]));
        assert_eq!(
            "x",
            find_parameter("foo", [".", "-zed", "z", "--foo=x"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(None, find_parameter("fo", [".", "-zed", "z", "--foo=x"]));
        assert_eq!(None, find_parameter("fooo", [".", "-zed", "z", "--foo=x"]));

        assert_eq!(
            "x",
            find_parameter("foo", [".", "--foo", "x"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(None, find_parameter("fo", [".", "--foo", "x"]));
        assert_eq!(None, find_parameter("fooo", [".", "--foo", "x"]));
        assert_eq!(
            "x",
            find_parameter("foo", [".", "-zed", "z", "--foo", "x"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(None, find_parameter("fo", [".", "-zed", "z", "--foo", "x"]));
        assert_eq!(
            None,
            find_parameter("fooo", [".", "-zed", "z", "--foo", "x"])
        );

        assert_eq!(None, find_parameter("foo", [".", "--foo"]));
        assert_eq!(None, find_parameter("foo", [".", "--bar=9", "--foo"]));

        assert_eq!(
            "x",
            find_parameter("foo", [".", "--foo=x", "--foo", "y"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(
            "x",
            find_parameter("foo", [".", "--foo", "x", "--foo", "y"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(
            "x",
            find_parameter("foo", [".", "--bar=9", "--foo=x", "--foo", "y"])
                .unwrap()
                .to_string_lossy()
        );
        assert_eq!(
            "x",
            find_parameter("foo", [".", "--bar=9", "--foo", "x", "--foo", "y"])
                .unwrap()
                .to_string_lossy()
        );

        assert_eq!(
            None,
            find_parameter("fo", [".", "--bar=9", "--foo=x", "--foo", "y"])
        );
        assert_eq!(
            None,
            find_parameter("fo", [".", "--bar=9", "--foo", "x", "--foo", "y"])
        );
    }
}