Rollup merge of #152897 - jdonszelmann:logging, r=jieyouxu

Add optional json logging

I became slightly frustrated with rust's logging output, and wanted to experiment a little with slightly postprocessing it with custom scripts. I think this is a pretty uninteresting change otherwise, shouldn't affect anyone else nor bother anyone. It's small enough that we can remove it again, nor is any of this stable or expected to be.

r? @jieyouxu

Author: JonathanBrouwer

Cargo.lock

@@ -5751,6 +5751,16 @@ dependencies = [
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-serde"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "704b1aeb7be0d0a84fc9828cae51dab5970fee5088f83d1dd7ee6f6246fc6ff1"
+dependencies = [
+ "serde",
+ "tracing-core",
+]
+
 [[package]]
 name = "tracing-subscriber"
 version = "0.3.20"
@@ -5762,12 +5772,15 @@ dependencies = [
  "once_cell",
  "parking_lot",
  "regex-automata",
+ "serde",
+ "serde_json",
  "sharded-slab",
  "smallvec",
  "thread_local",
  "tracing",
  "tracing-core",
  "tracing-log",
+ "tracing-serde",
 ]
 
 [[package]]

compiler/rustc_log/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 tracing = "0.1.41"
 tracing-core = "0.1.34"
-tracing-subscriber = { version = "0.3.3", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
+tracing-subscriber = { version = "0.3.3", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi", "json"] }
 tracing-tree = "0.3.1"
 # tidy-alphabetical-end
 

compiler/rustc_log/src/lib.rs

@@ -35,15 +35,18 @@
 
 use std::env::{self, VarError};
 use std::fmt::{self, Display};
+use std::fs::File;
 use std::io::{self, IsTerminal};
+use std::sync::Mutex;
 
 use tracing::dispatcher::SetGlobalDefaultError;
 use tracing::{Event, Subscriber};
-use tracing_subscriber::Registry;
 use tracing_subscriber::filter::{Directive, EnvFilter, LevelFilter};
 use tracing_subscriber::fmt::FmtContext;
-use tracing_subscriber::fmt::format::{self, FormatEvent, FormatFields};
+use tracing_subscriber::fmt::format::{self, FmtSpan, FormatEvent, FormatFields};
+use tracing_subscriber::fmt::writer::BoxMakeWriter;
 use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::{Layer, Registry};
 // Re-export tracing
 pub use {tracing, tracing_core, tracing_subscriber};
 
@@ -55,12 +58,15 @@ pub struct LoggerConfig {
     pub verbose_entry_exit: Result<String, VarError>,
     pub verbose_thread_ids: Result<String, VarError>,
     pub backtrace: Result<String, VarError>,
+    pub json: Result<String, VarError>,
+    pub output_target: Result<String, VarError>,
     pub wraptree: Result<String, VarError>,
     pub lines: Result<String, VarError>,
 }
 
 impl LoggerConfig {
     pub fn from_env(env: &str) -> Self {
+        // NOTE: documented in the dev guide. If you change this, also update it!
         LoggerConfig {
             filter: env::var(env),
             color_logs: env::var(format!("{env}_COLOR")),
@@ -69,6 +75,8 @@ impl LoggerConfig {
             backtrace: env::var(format!("{env}_BACKTRACE")),
             wraptree: env::var(format!("{env}_WRAPTREE")),
             lines: env::var(format!("{env}_LINES")),
+            json: env::var(format!("{env}_FORMAT_JSON")),
+            output_target: env::var(format!("{env}_OUTPUT_TARGET")),
         }
     }
 }
@@ -136,23 +144,59 @@ where
         Err(_) => false,
     };
 
-    let mut layer = tracing_tree::HierarchicalLayer::default()
-        .with_writer(io::stderr)
-        .with_ansi(color_logs)
-        .with_targets(true)
-        .with_verbose_exit(verbose_entry_exit)
-        .with_verbose_entry(verbose_entry_exit)
-        .with_indent_amount(2)
-        .with_indent_lines(lines)
-        .with_thread_ids(verbose_thread_ids)
-        .with_thread_names(verbose_thread_ids);
-
-    if let Ok(v) = cfg.wraptree {
-        match v.parse::<usize>() {
-            Ok(v) => layer = layer.with_wraparound(v),
-            Err(_) => return Err(Error::InvalidWraptree(v)),
+    let json = match cfg.json {
+        Ok(v) => &v == "1",
+        Err(_) => false,
+    };
+
+    let output_target: BoxMakeWriter = match cfg.output_target {
+        Ok(v) => match File::options().create(true).write(true).truncate(true).open(&v) {
+            Ok(i) => BoxMakeWriter::new(Mutex::new(i)),
+            Err(e) => {
+                eprintln!("couldn't open {v} as a log target: {e:?}");
+                BoxMakeWriter::new(io::stderr)
+            }
+        },
+        Err(_) => BoxMakeWriter::new(io::stderr),
+    };
+
+    let layer = if json {
+        let format = tracing_subscriber::fmt::format()
+            .json()
+            .with_span_list(true)
+            .with_source_location(true);
+
+        let fmt_layer = tracing_subscriber::fmt::layer()
+            .json()
+            .event_format(format)
+            .with_writer(output_target)
+            .with_target(true)
+            .with_ansi(false)
+            .with_thread_ids(verbose_thread_ids)
+            .with_thread_names(verbose_thread_ids)
+            .with_span_events(FmtSpan::ACTIVE);
+        Layer::boxed(fmt_layer)
+    } else {
+        let mut layer = tracing_tree::HierarchicalLayer::default()
+            .with_writer(output_target)
+            .with_ansi(color_logs)
+            .with_targets(true)
+            .with_verbose_exit(verbose_entry_exit)
+            .with_verbose_entry(verbose_entry_exit)
+            .with_indent_amount(2)
+            .with_indent_lines(lines)
+            .with_thread_ids(verbose_thread_ids)
+            .with_thread_names(verbose_thread_ids);
+
+        if let Ok(v) = cfg.wraptree {
+            match v.parse::<usize>() {
+                Ok(v) => layer = layer.with_wraparound(v),
+                Err(_) => return Err(Error::InvalidWraptree(v)),
+            }
         }
-    }
+
+        Layer::boxed(layer)
+    };
 
     let subscriber = build_subscriber();
     // NOTE: It is important to make sure that the filter is applied on the last layer

src/doc/rustc-dev-guide/src/tracing.md

@@ -12,6 +12,25 @@ To see the logs, you need to set the `RUSTC_LOG` environment variable to your lo
 The full syntax of the log filters can be found in the [rustdoc
 of `tracing-subscriber`](https://docs.rs/tracing-subscriber/0.2.24/tracing_subscriber/filter/struct.EnvFilter.html#directives).
 
+## Environment variables
+
+This is an overview of the environment variables rustc accepts to customize
+its tracing output. The definition of these can mostly be found in `compiler/rustc_log/src/lib.rs`.
+
+|  Name                     | Usage                                                                                                                   |
+| ------------------------- | ----------------------------------------------------------------------------------------------------------------------- |
+| `RUSTC_LOG`               | Tracing filters (see the rest of this page)                                                                             |
+| `RUSTC_LOG_COLOR`         | `always`, `never` or `auto`.                                                                                            |
+| `RUSTC_LOG_ENTRY_EXIT`    | if set and not '0', log span entry/exit.                                                                                |
+| `RUSTC_LOG_THREAD_IDS`    | if set and equal to '1', also log thread ids.                                                                           |
+| `RUSTC_LOG_BACKTRACE`     | Capture and print a backtrace if a trace is emitted with a target that matches the provided string value.               |
+| `RUSTC_LOG_LINES`         | If `1`, indents log lines based on depth.                                                                               |
+| `RUSTC_LOG_FORMAT_JSON`   | If `1`, outputs logs as JSON. The exact parameters can be found in `rustc_log/src/lib.rs` but the format is *UNSTABLE*. |
+| `RUSTC_LOG_OUTPUT_TARGET` | If provided, logs go to the provided file name instead of stderr.                                                       |
+
+
+
+
 ## Function level filters
 
 Lots of functions in rustc are annotated with

src/tools/tidy/src/deps.rs

@@ -450,6 +450,7 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "tracing-attributes",
     "tracing-core",
     "tracing-log",
+    "tracing-serde",
     "tracing-subscriber",
     "tracing-tree",
     "twox-hash",