capi: Bubble up blaze_syms allocation errors properly

convert_symbolizedresults_to_c() is a fallible function, but so far we
have not checked its result but just returned it straight away. That can
result in a NULL pointer being returned without an error code set.
Despite being highly unlikely (Rust code would just panic earlier on
allocation failure) as it's only our C layer that handles these
situations more gracefully, this is not ideal and counter to our stated
contract.
Make sure to check the function's return value and set the last error
accordingly.

Signed-off-by: Daniel Müller <[email protected]>

capi/src/symbolize.rs

@@ -829,7 +829,11 @@ unsafe fn blaze_symbolize_impl(
         }
         Ok(results) => {
             let result = convert_symbolizedresults_to_c(results);
-            let () = set_last_err(blaze_err::BLAZE_ERR_OK);
+            if result.is_null() {
+                let () = set_last_err(blaze_err::BLAZE_ERR_OUT_OF_MEMORY);
+            } else {
+                let () = set_last_err(blaze_err::BLAZE_ERR_OK);
+            }
             result
         }
         Err(err) => {
@@ -1348,6 +1352,8 @@ mod tests {
         // Empty list of symbols.
         let results = vec![];
         let syms = convert_symbolizedresults_to_c(results);
+        assert!(!syms.is_null());
+
         let () = touch_syms(syms);
         let () = unsafe { blaze_syms_free(syms) };
 
@@ -1379,6 +1385,7 @@ mod tests {
             _non_exhaustive: (),
         })];
         let syms = convert_symbolizedresults_to_c(results);
+        assert!(!syms.is_null());
         let () = touch_syms(syms);
         let () = unsafe { blaze_syms_free(syms) };
 
@@ -1402,6 +1409,7 @@ mod tests {
             Symbolized::Unknown(Reason::InvalidFileOffset),
         ];
         let syms = convert_symbolizedresults_to_c(results);
+        assert!(!syms.is_null());
         let () = touch_syms(syms);
         let () = unsafe { blaze_syms_free(syms) };
     }