From 04efb3cb53f853fd6fd560eb248940c59472f425 Mon Sep 17 00:00:00 2001
From: Robert Bastian <4706271+robertbastian@users.noreply.github.com>
Date: Mon, 27 Nov 2023 08:31:02 +0100
Subject: [PATCH] Ignoring pointer of empty slices (#375)

---
 macro/src/lib.rs                              | 20 ++++++++++++++++---
 ...t__tests__method_taking_mutable_slice.snap |  6 +++++-
 .../diplomat__tests__method_taking_slice.snap |  6 +++++-
 .../diplomat__tests__method_taking_str.snap   |  8 ++++++--
 4 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/macro/src/lib.rs b/macro/src/lib.rs
index 7c42ad00a..d2ddb3d58 100644
--- a/macro/src/lib.rs
+++ b/macro/src/lib.rs
@@ -102,14 +102,28 @@ fn gen_params_invocation(param: &ast::Param, expanded_params: &mut Vec<Expr>) {
             let tokens = if let ast::TypeName::PrimitiveSlice(_, mutability, _) = &param.ty {
                 match mutability {
                     ast::Mutability::Mutable => quote! {
-                        unsafe { core::slice::from_raw_parts_mut(#data_ident, #len_ident) }
+                        if #len_ident == 0 {
+                            &mut []
+                        } else {
+                            unsafe { core::slice::from_raw_parts_mut(#data_ident, #len_ident) }
+                        }
                     },
                     ast::Mutability::Immutable => quote! {
-                        unsafe { core::slice::from_raw_parts(#data_ident, #len_ident) }
+                        if #len_ident == 0 {
+                            &[]
+                        } else {
+                            unsafe { core::slice::from_raw_parts(#data_ident, #len_ident) }
+                        }
                     },
                 }
             } else {
-                quote! {unsafe { core::slice::from_raw_parts(#data_ident, #len_ident) } }
+                quote! {
+                    if #len_ident == 0 {
+                        &[]
+                    } else {
+                        unsafe { core::slice::from_raw_parts(#data_ident, #len_ident) }
+                    }
+                }
             };
             expanded_params.push(parse2(tokens).unwrap());
         }
diff --git a/macro/src/snapshots/diplomat__tests__method_taking_mutable_slice.snap b/macro/src/snapshots/diplomat__tests__method_taking_mutable_slice.snap
index 341f4b9b9..839a44824 100644
--- a/macro/src/snapshots/diplomat__tests__method_taking_mutable_slice.snap
+++ b/macro/src/snapshots/diplomat__tests__method_taking_mutable_slice.snap
@@ -13,7 +13,11 @@ mod ffi {
     use diplomat_runtime::*;
     #[no_mangle]
     extern "C" fn Foo_fill_slice(s_diplomat_data: *mut f64, s_diplomat_len: usize) {
-        Foo::fill_slice(unsafe { core::slice::from_raw_parts_mut(s_diplomat_data, s_diplomat_len) })
+        Foo::fill_slice(if s_diplomat_len == 0 {
+            &mut []
+        } else {
+            unsafe { core::slice::from_raw_parts_mut(s_diplomat_data, s_diplomat_len) }
+        })
     }
     #[no_mangle]
     extern "C" fn Foo_destroy(this: Box<Foo>) {}
diff --git a/macro/src/snapshots/diplomat__tests__method_taking_slice.snap b/macro/src/snapshots/diplomat__tests__method_taking_slice.snap
index f88b027e4..9b1e7cce4 100644
--- a/macro/src/snapshots/diplomat__tests__method_taking_slice.snap
+++ b/macro/src/snapshots/diplomat__tests__method_taking_slice.snap
@@ -13,7 +13,11 @@ mod ffi {
     use diplomat_runtime::*;
     #[no_mangle]
     extern "C" fn Foo_from_slice(s_diplomat_data: *const f64, s_diplomat_len: usize) {
-        Foo::from_slice(unsafe { core::slice::from_raw_parts(s_diplomat_data, s_diplomat_len) })
+        Foo::from_slice(if s_diplomat_len == 0 {
+            &[]
+        } else {
+            unsafe { core::slice::from_raw_parts(s_diplomat_data, s_diplomat_len) }
+        })
     }
     #[no_mangle]
     extern "C" fn Foo_destroy(this: Box<Foo>) {}
diff --git a/macro/src/snapshots/diplomat__tests__method_taking_str.snap b/macro/src/snapshots/diplomat__tests__method_taking_str.snap
index b3e4b3043..01666e41f 100644
--- a/macro/src/snapshots/diplomat__tests__method_taking_str.snap
+++ b/macro/src/snapshots/diplomat__tests__method_taking_str.snap
@@ -1,6 +1,6 @@
 ---
 source: macro/src/lib.rs
-expression: "rustfmt_code(&gen_bridge(parse_quote! {\n                            mod ffi\n                            {\n                                struct Foo {} impl Foo\n                                {\n                                    pub fn from_str(s : & DiplomatStr) { unimplemented! () }\n                                }\n                            }\n                        }).to_token_stream().to_string())"
+expression: "rustfmt_code(&gen_bridge(parse_quote! {\n                            mod ffi\n                            {\n                                struct Foo {} impl Foo\n                                { pub fn from_str(s : & DiplomatStr) { unimplemented! () } }\n                            }\n                        }).to_token_stream().to_string())"
 ---
 mod ffi {
     #[repr(C)]
@@ -13,7 +13,11 @@ mod ffi {
     use diplomat_runtime::*;
     #[no_mangle]
     extern "C" fn Foo_from_str(s_diplomat_data: *const u8, s_diplomat_len: usize) {
-        Foo::from_str(unsafe { core::slice::from_raw_parts(s_diplomat_data, s_diplomat_len) })
+        Foo::from_str(if s_diplomat_len == 0 {
+            &[]
+        } else {
+            unsafe { core::slice::from_raw_parts(s_diplomat_data, s_diplomat_len) }
+        })
     }
     #[no_mangle]
     extern "C" fn Foo_destroy(this: Box<Foo>) {}