Add support for RUST_LIB_BACKTRACE variable

src/lib.rs

@@ -36,6 +36,7 @@
 //! [medium](Verbosity::Medium) and `RUST_BACKTRACE=full` to
 //! [full](Verbosity::Full) verbosity levels.
 
+use std::env;
 use std::fs::File;
 use std::io::{BufRead, BufReader, ErrorKind};
 use std::panic::PanicInfo;
@@ -73,13 +74,26 @@ pub enum Verbosity {
 impl Verbosity {
     /// Get the verbosity level from the `RUST_BACKTRACE` env variable.
     pub fn from_env() -> Self {
-        match std::env::var("RUST_BACKTRACE") {
-            Ok(ref x) if x == "full" => Verbosity::Full,
-            Ok(_) => Verbosity::Medium,
-            Err(_) => Verbosity::Minimal,
+        Self::convert_env(env::var("RUST_BACKTRACE").ok())
+    }
+
+    pub fn lib_from_env() -> Self {
+        Self::convert_env(
+            env::var("RUST_LIB_BACKTRACE")
+                .or_else(|_| env::var("RUST_BACKTRACE"))
+                .ok(),
+        )
+    }
+
+    fn convert_env(env: Option<String>) -> Self {
+        match env {
+            Some(ref x) if x == "full" => Verbosity::Full,
+            Some(_) => Verbosity::Medium,
+            None => Verbosity::Minimal,
         }
     }
 }
+
 // ============================================================================================== //
 // [Panic handler and install logic]                                                              //
 // ============================================================================================== //
@@ -416,7 +430,9 @@ pub type Settings = BacktracePrinter;
 pub struct BacktracePrinter {
     message: String,
     verbosity: Verbosity,
+    lib_verbosity: Verbosity,
     strip_function_hash: bool,
+    is_panic_handler: bool,
     colors: ColorScheme,
     filters: Vec<Box<FilterCallback>>,
 }
@@ -425,9 +441,11 @@ impl Default for BacktracePrinter {
     fn default() -> Self {
         Self {
             verbosity: Verbosity::from_env(),
+            lib_verbosity: Verbosity::lib_from_env(),
             message: "The application panicked (crashed).".to_owned(),
             strip_function_hash: false,
             colors: ColorScheme::classic(),
+            is_panic_handler: false,
             filters: vec![Box::new(default_frame_filter)],
         }
     }
@@ -458,12 +476,20 @@ impl BacktracePrinter {
 
     /// Controls the verbosity level.
     ///
-    /// Defaults to `Verbosity::get_env()`.
+    /// Defaults to `Verbosity::from_env()`.
     pub fn verbosity(mut self, v: Verbosity) -> Self {
         self.verbosity = v;
         self
     }
 
+    /// Controls the lib verbosity level.
+    ///
+    /// Defaults to `Verbosity::lib_from_env()`.
+    pub fn lib_verbosity(mut self, v: Verbosity) -> Self {
+        self.lib_verbosity = v;
+        self
+    }
+
     /// Controls whether the hash part of functions is stripped.
     ///
     /// Defaults to `false`.
@@ -514,9 +540,10 @@ impl BacktracePrinter {
     ///
     /// This can be used if you want to combine the handler with other handlers.
     pub fn into_panic_handler(
-        self,
+        mut self,
         out: impl WriteColor + Sync + Send + 'static,
     ) -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
+        self.is_panic_handler = true;
         let out_stream_mutex = Mutex::new(out);
         Box::new(move |pi| {
             let mut lock = out_stream_mutex.lock().unwrap();
@@ -653,15 +680,15 @@ impl BacktracePrinter {
         }
 
         // Print some info on how to increase verbosity.
-        if self.verbosity == Verbosity::Minimal {
+        if self.current_verbosity() == Verbosity::Minimal {
             write!(out, "\nBacktrace omitted. Run with ")?;
             out.set_color(&self.colors.env_var)?;
             write!(out, "RUST_BACKTRACE=1")?;
             out.reset()?;
             writeln!(out, " environment variable to display it.")?;
         }
-        if self.verbosity <= Verbosity::Medium {
-            if self.verbosity == Verbosity::Medium {
+        if self.current_verbosity() <= Verbosity::Medium {
+            if self.current_verbosity() == Verbosity::Medium {
                 // If exactly medium, no newline was printed before.
                 writeln!(out)?;
             }
@@ -673,12 +700,20 @@ impl BacktracePrinter {
             writeln!(out, " to include source snippets.")?;
         }
 
-        if self.verbosity >= Verbosity::Medium {
+        if self.current_verbosity() >= Verbosity::Medium {
             self.print_trace(&backtrace::Backtrace::new(), out)?;
         }
 
         Ok(())
     }
+
+    fn current_verbosity(&self) -> Verbosity {
+        if self.is_panic_handler {
+            self.verbosity
+        } else {
+            self.lib_verbosity
+        }
+    }
 }
 
 // ============================================================================================== //