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tracing: fix macros "use of moved value" with log #1823

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merged 12 commits into from
Jan 29, 2022
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tracing: Move LogValueSet into __macro_support
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Skepfyr committed Jan 11, 2022
commit 68b56d0d8fa82ea70f6c31174afc3885aebb148d
50 changes: 49 additions & 1 deletion tracing/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -980,7 +980,8 @@ pub mod __macro_support {
use crate::{collect::Interest, Metadata};
use core::fmt;
use core::sync::atomic::{AtomicUsize, Ordering};
use tracing_core::Once;
use tracing_core::field::{ValueSet, Visit};
use tracing_core::{Field, Once};

/// Callsite implementation used by macro-generated code.
///
Expand Down Expand Up @@ -1109,6 +1110,53 @@ pub mod __macro_support {
.finish()
}
}

/// Utility to format [`ValueSet`] for logging, used by macro-generated code.
///
/// /!\ WARNING: This is *not* a stable API! /!\
/// This type, and all code contained in the `__macro_support` module, is
/// a *private* API of `tracing`. It is exposed publicly because it is used
/// by the `tracing` macros, but it is not part of the stable versioned API.
/// Breaking changes to this module may occur in small-numbered versions
/// without warning.
#[derive(Debug)]
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pub struct LogValueSet<'a>(pub &'a ValueSet<'a>);
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i have a slight preference for giving this a new constructor, rather than a pub field, so that we can add new fields to it while still supporting earlier versions of the macros. however, i doubt this is an issue in practice, so it may not really matter...

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impl<'a> std::fmt::Display for LogValueSet<'a> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let mut visit = LogVisitor {
f,
is_first: true,
result: Ok(()),
};
self.0.record(&mut visit);
visit.result
}
}

struct LogVisitor<'a, 'b> {
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f: &'a mut std::fmt::Formatter<'b>,
is_first: bool,
result: std::fmt::Result,
}

impl Visit for LogVisitor<'_, '_> {
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fn record_debug(&mut self, field: &Field, value: &dyn std::fmt::Debug) {
let res = if self.is_first {
self.is_first = false;
if field.name() == "message" {
write!(self.f, "{:?}", value)
} else {
write!(self.f, "{}={:?}", field.name(), value)
}
} else {
write!(self.f, " {}={:?}", field.name(), value)
};
Comment on lines +1154 to +1163
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nit, take it or leave it: this might look slightly nicer as a match?

Suggested change
let res = if self.is_first {
self.is_first = false;
if field.name() == "message" {
write!(self.f, "{:?}", value)
} else {
write!(self.f, "{}={:?}", field.name(), value)
}
} else {
write!(self.f, " {}={:?}", field.name(), value)
};
let res = match field.name() {
"message" if self.is_first() => write!(self.f, "{:?}", value),
"message" => write!(self.f, " {:?}", value),
name if self.is_first => write!(self.f, "{}={:?}", name, value),
name => write!(self.f, " {}={:?}", name, value,
};
self.is_first = false;

though, up to you

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I prefer the explicit something is only weird about the first one of the if. However, your snippet does produce a different output to mine, in the case of message not being the first field. Mine would produce:

foo=bar message=Hi! baz=quux

whereas yours would produce:

foo=bar Hi! baz=quux

Is that behaviour ok, or should I change it to be in line with yours?

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in practice, the valueset! macro will always re-order the message field to come first, so it doesn't really matter whether we handle it differently if it isn't the first field. i don't have a strong opinion about this code, so it's fine to leave it the way you had it if you prefer.

if let Err(err) = res {
self.result = self.result.and(Err(err));
}
}
}
}

mod sealed {
Expand Down
38 changes: 2 additions & 36 deletions tracing/src/macros.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2172,41 +2172,7 @@ macro_rules! __tracing_log {
macro_rules! __tracing_log {
(target: $target:expr, $level:expr, $value_set:ident ) => {
$crate::if_log_enabled! { $level, {
use $crate::{log, field};
struct LogValueSet<'a>(&'a field::ValueSet<'a>);
impl<'a> std::fmt::Display for LogValueSet<'a> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let mut visit = Visit {
f,
is_first: true,
result: Ok(()),
};
self.0.record(&mut visit);
visit.result
}
}
struct Visit<'a, 'b> {
f: &'a mut std::fmt::Formatter<'b>,
is_first: bool,
result: std::fmt::Result,
}
impl field::Visit for Visit<'_, '_> {
fn record_debug(&mut self, field: &field::Field, value: &dyn std::fmt::Debug) {
let res = if self.is_first {
self.is_first = false;
if field.name() == "message" {
write!(self.f, "{:?}", value)
} else {
write!(self.f, "{}={:?}", field.name(), value)
}
} else {
write!(self.f, " {}={:?}", field.name(), value)
};
if let Err(err) = res {
self.result = self.result.and(Err(err));
}
}
}
use $crate::log;
let level = $crate::level_to_log!($level);
if level <= log::max_level() {
let log_meta = log::Metadata::builder()
Expand All @@ -2220,7 +2186,7 @@ macro_rules! __tracing_log {
.module_path(Some(module_path!()))
.line(Some(line!()))
.metadata(log_meta)
.args(format_args!("{}", LogValueSet(&$value_set)))
.args(format_args!("{}", $crate::__macro_support::LogValueSet(&$value_set)))
.build());
}
}
Expand Down