455723c638
This teaches `format_args!` how to interpret format printf- and
shell-style format directives. This is used in cases where there are
unused formatting arguments, and the reason for that *might* be because
the programmer is trying to use the wrong kind of formatting string.
This was prompted by an issue encountered by simulacrum on the #rust IRC
channel. In short: although `println!` told them that they weren't using
all of the conversion arguments, the problem was in using printf-syle
directives rather than ones `println!` would undertand.
Where possible, `format_args!` will tell the programmer what they should
use instead. For example, it will suggest replacing `%05d` with `{:0>5}`,
or `%2$.*3$s` with `{1:.3$}`. Even if it cannot suggest a replacement,
it will explicitly note that Rust does not support that style of directive,
and direct the user to the `std::fmt` documentation.
60 lines
2.3 KiB
Rust
60 lines
2.3 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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fn main() {
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// bad arguments to the format! call
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format!("{}"); //~ ERROR: invalid reference to argument
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format!("{1}", 1); //~ ERROR: invalid reference to argument `1`
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//~^ ERROR: argument never used
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format!("{foo}"); //~ ERROR: no argument named `foo`
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format!("", 1, 2); //~ ERROR: multiple unused formatting arguments
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format!("{}", 1, 2); //~ ERROR: argument never used
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format!("{1}", 1, 2); //~ ERROR: argument never used
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format!("{}", 1, foo=2); //~ ERROR: named argument never used
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format!("{foo}", 1, foo=2); //~ ERROR: argument never used
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format!("", foo=2); //~ ERROR: named argument never used
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format!("{foo}", foo=1, foo=2); //~ ERROR: duplicate argument
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format!("", foo=1, 2); //~ ERROR: positional arguments cannot follow
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// bad number of arguments, see #15780
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format!("{0}");
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//~^ ERROR invalid reference to argument `0` (no arguments given)
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format!("{0} {1}", 1);
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//~^ ERROR invalid reference to argument `1` (there is 1 argument)
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format!("{0} {1} {2}", 1, 2);
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//~^ ERROR invalid reference to argument `2` (there are 2 arguments)
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format!("{0} {1}");
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//~^ ERROR invalid reference to argument `0` (no arguments given)
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//~^^ ERROR invalid reference to argument `1` (no arguments given)
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// bad named arguments, #35082
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format!("{valuea} {valueb}", valuea=5, valuec=7);
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//~^ ERROR there is no argument named `valueb`
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//~^^ ERROR named argument never used
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// bad syntax of the format string
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format!("{"); //~ ERROR: expected `'}'` but string was terminated
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format!("foo } bar"); //~ ERROR: unmatched `}` found
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format!("foo }"); //~ ERROR: unmatched `}` found
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format!("foo %s baz", "bar"); //~ ERROR: argument never used
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}
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