improve logging

build.rs

@@ -1,4 +1,5 @@
 fn main() {
+    generate_filter_snippet();
     linker_be_nice();
     // make sure linkall.x is the last linker script (otherwise might cause problems with flip-link)
     println!("cargo:rustc-link-arg=-Tlinkall.x");
@@ -68,3 +69,165 @@ fn linker_be_nice() {
         std::env::current_exe().unwrap().display()
     );
 }
+
+// Taken over from esp_println because impossible to just extend their existing env logger.
+// https://github.com/esp-rs/esp-hal/blob/8fa6d7e985e724d6ad998e34307429b0920da370/esp-println/build.rs
+fn generate_filter_snippet() {
+    use log::LevelFilter;
+    use std::{env, path::Path};
+
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    let dest_path = Path::new(&out_dir).join("log_filter.rs");
+
+    let filter = env::var("ESP_LOG");
+    let snippet = if let Ok(filter) = filter {
+        let res = parse_spec(&filter);
+
+        if !res.errors.is_empty() {
+            panic!("Error parsing `ESP_LOG`: {:?}", res.errors);
+        } else {
+            let max = res
+                .directives
+                .iter()
+                .map(|v| v.level)
+                .max()
+                .unwrap_or(LevelFilter::Off);
+            let max = match max {
+                LevelFilter::Off => "Off",
+                LevelFilter::Error => "Error",
+                LevelFilter::Warn => "Warn",
+                LevelFilter::Info => "Info",
+                LevelFilter::Debug => "Debug",
+                LevelFilter::Trace => "Trace",
+            };
+
+            let mut snippet = String::new();
+
+            snippet.push_str(&format!(
+                "pub(crate) const FILTER_MAX: log::LevelFilter = log::LevelFilter::{max};"
+            ));
+
+            snippet
+                .push_str("pub(crate) fn is_enabled(level: log::Level, _target: &str) -> bool {");
+
+            let mut global_level = None;
+            for directive in res.directives {
+                let level = match directive.level {
+                    LevelFilter::Off => "Off",
+                    LevelFilter::Error => "Error",
+                    LevelFilter::Warn => "Warn",
+                    LevelFilter::Info => "Info",
+                    LevelFilter::Debug => "Debug",
+                    LevelFilter::Trace => "Trace",
+                };
+
+                if let Some(name) = directive.name {
+                    // If a prefix matches, don't continue to the next directive
+                    snippet.push_str(&format!(
+                        "if _target.starts_with(\"{name}\") {{ return level <= log::LevelFilter::{level}; }}"
+                    ));
+                } else {
+                    if global_level.is_some() {
+                        panic!("Multiple global log levels specified in `ESP_LOG`");
+                    }
+                    global_level = Some(level);
+                }
+            }
+
+            // Place the fallback rule at the end
+            if let Some(level) = global_level {
+                snippet.push_str(&format!("level <= log::LevelFilter::{level}"));
+            } else {
+                snippet.push_str(" false");
+            }
+            snippet.push('}');
+            snippet
+        }
+    } else {
+        "pub(crate) const FILTER_MAX: log::LevelFilter = log::LevelFilter::Off; pub(crate) fn is_enabled(_level: log::Level, _target: &str) -> bool { true }".to_string()
+    };
+
+    std::fs::write(&dest_path, &snippet).unwrap();
+}
+
+#[derive(Default, Debug)]
+struct ParseResult {
+    pub(crate) directives: Vec<Directive>,
+    pub(crate) errors: Vec<String>,
+}
+
+impl ParseResult {
+    fn add_directive(&mut self, directive: Directive) {
+        self.directives.push(directive);
+    }
+
+    fn add_error(&mut self, message: String) {
+        self.errors.push(message);
+    }
+}
+
+#[derive(Debug)]
+struct Directive {
+    pub(crate) name: Option<String>,
+    pub(crate) level: log::LevelFilter,
+}
+
+/// Parse a logging specification string (e.g:
+/// `crate1,crate2::mod3,crate3::x=error/foo`) and return a vector with log
+/// directives.
+fn parse_spec(spec: &str) -> ParseResult {
+    use log::LevelFilter;
+
+    let mut result = ParseResult::default();
+
+    let mut parts = spec.split('/');
+    let mods = parts.next();
+
+    if let Some(m) = mods {
+        for s in m.split(',').map(|ss| ss.trim()) {
+            if s.is_empty() {
+                continue;
+            }
+            let mut parts = s.split('=');
+            let (log_level, name) =
+                match (parts.next(), parts.next().map(|s| s.trim()), parts.next()) {
+                    (Some(part0), None, None) => {
+                        // if the single argument is a log-level string or number,
+                        // treat that as a global fallback
+                        match part0.parse() {
+                            Ok(num) => (num, None),
+                            Err(_) => (LevelFilter::max(), Some(part0)),
+                        }
+                    }
+                    (Some(part0), Some(""), None) => (LevelFilter::max(), Some(part0)),
+                    (Some(part0), Some(part1), None) => {
+                        if let Ok(num) = part1.parse() {
+                            (num, Some(part0))
+                        } else {
+                            result.add_error(format!("invalid logging spec '{part1}'"));
+                            continue;
+                        }
+                    }
+                    _ => {
+                        result.add_error(format!("invalid logging spec '{s}'"));
+                        continue;
+                    }
+                };
+
+            result.add_directive(Directive {
+                name: name.map(|s| s.to_owned()),
+                level: log_level,
+            });
+        }
+    }
+
+    // Sort by length so that the most specific prefixes come first
+    result
+        .directives
+        .sort_by(|a, b| match (a.name.as_ref(), b.name.as_ref()) {
+            (Some(a), Some(b)) => b.len().cmp(&a.len()),
+            _ => std::cmp::Ordering::Equal,
+        });
+
+    result
+}