Test that externally-defined functions going safe -> unsafe are caught.

test_crates/safe_vs_unsafe_extern_fn/new/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "safe_vs_unsafe_extern_fn"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/safe_vs_unsafe_extern_fn/new/src/lib.rs

@@ -0,0 +1,29 @@
+#![feature(unsafe_extern_blocks)]  // Remove after our lowest tested Rust version is 1.82+.
+
+unsafe extern "C" {
+    pub fn originally_legacy_now_unsafe_extern_and_implicit_unsafe();
+
+    pub unsafe fn originally_legacy_now_unsafe_extern_and_explicit_unsafe();
+
+    pub safe fn originally_legacy_now_unsafe_extern_and_safe();
+}
+
+unsafe extern "C" {
+    pub fn originally_explicit_now_implicit_unsafe();
+
+    pub unsafe fn originally_implicit_now_explicit_unsafe();
+
+    pub fn originally_safe_now_implicit_unsafe();
+
+    pub unsafe fn originally_safe_now_explicit_unsafe();
+}
+
+// This is the "legacy" way of specifying `extern`.
+extern "C" {
+    pub fn originally_implicit_unsafe_now_legacy();
+
+    pub fn originally_explicit_unsafe_now_legacy();
+
+    // This is a breaking change!
+    pub fn originally_safe_now_legacy();
+}

test_crates/safe_vs_unsafe_extern_fn/old/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+publish = false
+name = "safe_vs_unsafe_extern_fn"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

test_crates/safe_vs_unsafe_extern_fn/old/src/lib.rs

@@ -0,0 +1,27 @@
+#![feature(unsafe_extern_blocks)]  // Remove after our lowest tested Rust version is 1.82+.
+
+extern "C" {
+    pub fn originally_legacy_now_unsafe_extern_and_implicit_unsafe();
+
+    pub fn originally_legacy_now_unsafe_extern_and_explicit_unsafe();
+
+    pub fn originally_legacy_now_unsafe_extern_and_safe();
+}
+
+unsafe extern "C" {
+    pub unsafe fn originally_explicit_now_implicit_unsafe();
+
+    pub fn originally_implicit_now_explicit_unsafe();
+
+    pub safe fn originally_safe_now_implicit_unsafe();
+
+    pub safe fn originally_safe_now_explicit_unsafe();
+}
+
+unsafe extern "C" {
+    pub fn originally_implicit_unsafe_now_legacy();
+
+    pub unsafe fn originally_explicit_unsafe_now_legacy();
+
+    pub safe fn originally_safe_now_legacy();
+}

test_outputs/query_execution/function_unsafe_added.snap

@@ -15,4 +15,36 @@ expression: "&query_execution_results"
       "visibility_limit": String("public"),
     },
   ],
+  "./test_crates/safe_vs_unsafe_extern_fn/": [
+    {
+      "name": String("originally_safe_now_implicit_unsafe"),
+      "path": List([
+        String("safe_vs_unsafe_extern_fn"),
+        String("originally_safe_now_implicit_unsafe"),
+      ]),
+      "span_begin_line": Uint64(16),
+      "span_filename": String("src/lib.rs"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "name": String("originally_safe_now_explicit_unsafe"),
+      "path": List([
+        String("safe_vs_unsafe_extern_fn"),
+        String("originally_safe_now_explicit_unsafe"),
+      ]),
+      "span_begin_line": Uint64(18),
+      "span_filename": String("src/lib.rs"),
+      "visibility_limit": String("public"),
+    },
+    {
+      "name": String("originally_safe_now_legacy"),
+      "path": List([
+        String("safe_vs_unsafe_extern_fn"),
+        String("originally_safe_now_legacy"),
+      ]),
+      "span_begin_line": Uint64(28),
+      "span_filename": String("src/lib.rs"),
+      "visibility_limit": String("public"),
+    },
+  ],
 }