cabi: Add getter for error debug info (#775)

Author: maxbrunet

CHANGELOG.md

@@ -5,6 +5,7 @@ All notable changes to MiniJinja are documented here.
 ## 2.10.0
 
 - Fix incorrect permissions when `--output` is used in the CLI.  #772
+- Added `mj_err_get_debug_info` to the C-ABI.  #775
 
 ## 2.9.0
 

minijinja-cabi/include/minijinja.h

@@ -207,6 +207,11 @@ void mj_env_set_undefined_behavior(struct mj_env *env,
  */
 MINIJINJA_API void mj_err_clear(void);
 
+/*
+ Returns the error's debug info if there is an error.
+ */
+MINIJINJA_API char *mj_err_get_debug_info(void);
+
 /*
  Returns the error's description if there is an error.
  */

minijinja-cabi/src/error.rs

@@ -1,6 +1,7 @@
 use std::cell::RefCell;
 use std::error::Error as _;
 use std::ffi::{c_char, CString};
+use std::fmt::Write;
 use std::ptr;
 
 use minijinja::{Error, ErrorKind};
@@ -48,6 +49,37 @@ pub extern "C" fn mj_err_print() -> bool {
     })
 }
 
+/// Returns the error's debug info if there is an error.
+///
+/// The value must be freed with `mj_str_free`.
+#[no_mangle]
+pub unsafe extern "C" fn mj_err_get_debug_info() -> *mut c_char {
+    LAST_ERROR
+        .with_borrow(|x| {
+            x.as_ref()
+                .and_then(|x| {
+                    let mut info = String::new();
+                    if x.name().is_some() {
+                        writeln!(info, "{}", x.display_debug_info()).unwrap();
+                    }
+                    let mut source_opt = x.source();
+                    while let Some(source) = source_opt {
+                        writeln!(info, "\ncaused by: {source}").unwrap();
+                        if let Some(source) = source.downcast_ref::<Error>() {
+                            if source.name().is_some() {
+                                writeln!(info, "{}", source.display_debug_info()).unwrap();
+                            }
+                        }
+                        source_opt = source.source();
+                    }
+                    info.into()
+                })
+                .and_then(|info| CString::new(info).ok())
+                .map(|cstr| cstr.into_raw())
+        })
+        .unwrap_or(ptr::null_mut())
+}
+
 /// Returns the error's description if there is an error.
 ///
 /// The value must be freed with `mj_str_free`.