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Add a dedicated debug-logging option to config.toml #76588

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Merged
merged 3 commits into from
Sep 13, 2020
Merged

Add a dedicated debug-logging option to config.toml #76588

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15aa6f3
add debug-logging to config.toml
guswynn Sep 10, 2020
56f5c7f
comments + add max_level_info so false works with debug_assertions on
guswynn Sep 11, 2020
0be66d7
just max_level_info
guswynn Sep 11, 2020
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2 changes: 1 addition & 1 deletion compiler/rustc_driver/Cargo.toml
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Expand Up @@ -38,4 +38,4 @@ winapi = { version = "0.3", features = ["consoleapi", "debugapi", "processenv"]

[features]
llvm = ['rustc_interface/llvm']
release_max_level_info = ['tracing/release_max_level_info']
release_max_level_info = ['tracing/release_max_level_info', 'tracing/max_level_info']
6 changes: 3 additions & 3 deletions config.toml.example
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Expand Up @@ -321,19 +321,19 @@
# binary, otherwise they are omitted.
#
# Defaults to rust.debug value
#debug-assertions = false
#debug-assertions = debug

# Whether or not debug assertions are enabled for the standard library.
# Overrides the `debug-assertions` option, if defined.
#
# Defaults to rust.debug-assertions value
#debug-assertions-std = false
#debug-assertions-std = debug-assertions

# Whether or not to leave debug! and trace! calls in the rust binary.
# Overrides the `debug-assertions` option, if defined.
#
# Defaults to rust.debug-assertions value
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Hm, so this brings up two interesting questions:

  • Should we default to this being on? If you're doing a lot of rustc development, it can certainly be helpful to have debug logs, but it can also be a pretty annoying slowdown (IIRC, benchmarks show 5-10%).
  • Show we tie to to the old way of turning it on, i.e., debug-assertions?

cc @jyn514, we might want an MCP or similar here to figure out what people think good defaults would be.

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@jyn514 jyn514 Sep 11, 2020 •
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I think it should start as off-by-default. There was a lot of discussion in #76588 about enabling logging and it was almost a 10% perf hit on some benchmarks: https://perf.rust-lang.org/compare.html?start=22e6099330cde0e7b1529774fe27874f8326de7a&end=ededceef5651050bda1a2058af270da498bb1333.

That said, I would love to get the perf impact low enough that this can be on by default (or even always on).

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That said, I would love to get the perf impact low enough that this can be on by default (or even always on).

One possible way to do this is to separate debug! from trace! and have that be opt-in instead. AFAIK most of the compiler uses debug! currently, but I separate the two in rustdoc and it's worked very well. In particular, collect_intra_doc_links prints ludicrous amounts of info with trace but only ~15 lines or so per module with debug: https://github.com/rust-lang/rust/blob/master/src/librustdoc/passes/collect_intra_doc_links.rs#L647

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As it is implemented now, it should be off by default, and on wit debug-assertions, which matched exactly the semantics of the current config.toml

#debug-logging = true
#debug-logging = debug-assertions

# Debuginfo level for most of Rust code, corresponds to the `-C debuginfo=N` option of `rustc`.
# `0` - no debug info
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