Add foreign formatting directive detection.

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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.

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This commit is contained in:

Daniel Keep

2016-11-11 15:23:15 +11:00

parent e96b9d2bb4

commit 455723c638

6 changed files with 1163 additions and 2 deletions

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src/libsyntax_ext/format_foreign.rs Normal file

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