44440e5c18
fmt::Show is for debugging, and can and should be implemented for
all public types. This trait is used with `{:?}` syntax. There still
exists #[derive(Show)].
fmt::String is for types that faithfully be represented as a String.
Because of this, there is no way to derive fmt::String, all
implementations must be purposeful. It is used by the default format
syntax, `{}`.
This will break most instances of `{}`, since that now requires the type
to impl fmt::String. In most cases, replacing `{}` with `{:?}` is the
correct fix. Types that were being printed specifically for users should
receive a fmt::String implementation to fix this.
Part of #20013
[breaking-change]
58 lines
2.3 KiB
Rust
58 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: 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!("{0:x} {0:X}", 1); //~ ERROR: redeclared with type `X`
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format!("{foo:x} {foo:X}", foo=1); //~ ERROR: redeclared with type `X`
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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 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!(); //~ ERROR: requires at least a format string argument
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format!("" 1); //~ ERROR: expected token: `,`
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format!("", 1 1); //~ ERROR: expected token: `,`
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}
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