Add a feature to stop linking the default panic

CHANGELOG.md

@@ -9,11 +9,13 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - [#821]: Cleanup
 - [#813]: doc: add note for the alloc feature flag
+- [#812]: `defmt`: Add a feature to stop linking a default panic handler
 - [#811]: `book`: Add some examples for byte slice/array hints as well
 - [#800]: `defmt-macros`: Fix generic trait bounds in Format derive macro
 
 [#821]: https://github.com/knurling-rs/defmt/pull/821
 [#813]: https://github.com/knurling-rs/defmt/pull/813
+[#812]: https://github.com/knurling-rs/defmt/pull/812
 [#811]: https://github.com/knurling-rs/defmt/pull/811
 [#800]: https://github.com/knurling-rs/defmt/pull/800
 

defmt/Cargo.toml

@@ -20,6 +20,7 @@ version = "0.3.6"
 [features]
 alloc = []
 ip_in_core = []
+avoid-default-panic = []
 
 # Encoding feature flags. These should only be set by end-user crates, not by library crates.
 #

defmt/build.rs

@@ -1,9 +1,16 @@
 use std::{env, error::Error, fs, path::PathBuf};
 
 fn main() -> Result<(), Box<dyn Error>> {
+    // Read the linker script
+    let mut linker_script = fs::read_to_string("defmt.x.in")?;
+
+    // Optionally exclude default panic handler
+    if cfg!(feature = "avoid-default-panic") {
+        linker_script = avoid_default_panic(linker_script);
+    }
+
     // Put the linker script somewhere the linker can find it
     let out = &PathBuf::from(env::var("OUT_DIR")?);
-    let linker_script = fs::read_to_string("defmt.x.in")?;
     fs::write(out.join("defmt.x"), linker_script)?;
     println!("cargo:rustc-link-search={}", out.display());
     let target = env::var("TARGET")?;
@@ -23,3 +30,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     }
     Ok(())
 }
+
+fn avoid_default_panic(linker_script: String) -> String {
+    linker_script.replacen("PROVIDE(_defmt_panic = __defmt_default_panic);", "", 1)
+}