feat(core): expose init_logger publicly for uniform preprocessor logging

Preprocessor authors can now call `mdbook_core::utils::init_logger()` to use
mdBook's logger configuration (MDBOOK_LOG env var, INFO default, silenced noisy
deps like handlebars/html5ever).

Make mdbook-core standalone:
- Pin explicit `tracing-subscriber` dep (matches workspace version)
- Remove redundant workspace deps/transitive resolutions

Closes #2049

Co-authored-by: BlackboxAI <code@blackbox.ai>

Author: jhult

Cargo.lock

@@ -66,7 +66,6 @@ toml = "1.0.3"
 topological-sort = "0.2.2"
 tower-http = "0.6.8"
 tracing = "0.1.44"
-tracing-subscriber = { version = "0.3.22", features = ["env-filter"] }
 walkdir = "2.5.0"
 
 [package]
@@ -96,7 +95,6 @@ mdbook-driver.workspace = true
 mdbook-html.workspace = true
 opener.workspace = true
 tracing.workspace = true
-tracing-subscriber.workspace = true
 
 # Watch feature
 ignore = { workspace = true, optional = true }

Cargo.toml

@@ -14,6 +14,7 @@ serde.workspace = true
 serde_json.workspace = true
 toml.workspace = true
 tracing.workspace = true
+tracing-subscriber = { version = "0.3.22", features = ["env-filter"] }
 
 [dev-dependencies]
 tempfile.workspace = true

crates/mdbook-core/Cargo.toml

@@ -8,6 +8,49 @@ pub mod fs;
 mod html;
 mod toml_ext;
 
+/// Initialize the logger with mdBook's default configuration.
+///
+/// This function sets up a tracing subscriber that:
+/// - Uses the `MDBOOK_LOG` environment variable for filtering (or defaults to INFO level)
+/// - Silences noisy dependencies (handlebars, html5ever) unless explicitly requested
+/// - Writes to stderr
+/// - Shows the target only when MDBOOK_LOG is set
+///
+/// This is useful for preprocessor authors who want consistent logging
+/// with mdBook's internal logging.
+pub fn init_logger() {
+    let filter = tracing_subscriber::EnvFilter::builder()
+        .with_env_var("MDBOOK_LOG")
+        .with_default_directive(tracing_subscriber::filter::LevelFilter::INFO.into())
+        .from_env_lossy();
+    let log_env = std::env::var("MDBOOK_LOG");
+    // Silence some particularly noisy dependencies unless the user
+    // specifically asks for them.
+    let silence_unless_specified = |filter: tracing_subscriber::EnvFilter, target| {
+        if !log_env.as_ref().map_or(false, |s| {
+            s.split(',').any(|directive| directive.starts_with(target))
+        }) {
+            filter.add_directive(format!("{target}=warn").parse().unwrap())
+        } else {
+            filter
+        }
+    };
+    let filter = silence_unless_specified(filter, "handlebars");
+    let filter = silence_unless_specified(filter, "html5ever");
+
+    // Don't show the target by default, since it generally isn't useful
+    // unless you are overriding the level.
+    let with_target = log_env.is_ok();
+
+    tracing_subscriber::fmt()
+        .without_time()
+        .with_ansi(std::io::IsTerminal::is_terminal(&std::io::stderr()))
+        .with_writer(std::io::stderr)
+        .with_env_filter(filter)
+        .with_target(with_target)
+        .init();
+}
+
 pub(crate) use self::toml_ext::TomlExt;
 
 pub use self::html::{escape_html, escape_html_attribute};

crates/mdbook-core/src/utils/mod.rs

@@ -16,7 +16,7 @@ mod cmd;
 const VERSION: &str = concat!("v", clap::crate_version!());
 
 fn main() {
-    init_logger();
+    utils::init_logger();
 
     let command = create_clap_command();
 
@@ -90,39 +90,6 @@ fn create_clap_command() -> Command {
     app
 }
 
-fn init_logger() {
-    let filter = tracing_subscriber::EnvFilter::builder()
-        .with_env_var("MDBOOK_LOG")
-        .with_default_directive(tracing_subscriber::filter::LevelFilter::INFO.into())
-        .from_env_lossy();
-    let log_env = std::env::var("MDBOOK_LOG");
-    // Silence some particularly noisy dependencies unless the user
-    // specifically asks for them.
-    let silence_unless_specified = |filter: tracing_subscriber::EnvFilter, target| {
-        if !log_env.as_ref().map_or(false, |s| {
-            s.split(',').any(|directive| directive.starts_with(target))
-        }) {
-            filter.add_directive(format!("{target}=warn").parse().unwrap())
-        } else {
-            filter
-        }
-    };
-    let filter = silence_unless_specified(filter, "handlebars");
-    let filter = silence_unless_specified(filter, "html5ever");
-
-    // Don't show the target by default, since it generally isn't useful
-    // unless you are overriding the level.
-    let with_target = log_env.is_ok();
-
-    tracing_subscriber::fmt()
-        .without_time()
-        .with_ansi(std::io::IsTerminal::is_terminal(&std::io::stderr()))
-        .with_writer(std::io::stderr)
-        .with_env_filter(filter)
-        .with_target(with_target)
-        .init();
-}
-
 fn get_book_dir(args: &ArgMatches) -> PathBuf {
     if let Some(p) = args.get_one::<PathBuf>("dir") {
         // Check if path is relative from current dir, or absolute...