transpile: Add snapshot test for main function

Author: Rua

c2rust-transpile/tests/snapshots/main.c

@@ -0,0 +1,3 @@
+int main(int argc, char **argv, char **envp) {
+    return 0;
+}

c2rust-transpile/tests/snapshots/[email protected]

@@ -0,0 +1,51 @@
+---
+source: c2rust-transpile/tests/snapshots.rs
+expression: cat tests/snapshots/main.rs
+input_file: c2rust-transpile/tests/snapshots/main.c
+---
+#![allow(
+    dead_code,
+    non_camel_case_types,
+    non_snake_case,
+    non_upper_case_globals,
+    unused_assignments,
+    unused_mut
+)]
+unsafe fn main_0(
+    mut argc: ::core::ffi::c_int,
+    mut argv: *mut *mut ::core::ffi::c_char,
+    mut envp: *mut *mut ::core::ffi::c_char,
+) -> ::core::ffi::c_int {
+    return 0 as ::core::ffi::c_int;
+}
+pub fn main() {
+    let mut args_strings: Vec<Vec<u8>> = ::std::env::args()
+        .map(|arg| {
+            ::std::ffi::CString::new(arg)
+                .expect("Failed to convert argument into CString.")
+                .into_bytes_with_nul()
+        })
+        .collect();
+    let mut args_ptrs: Vec<*mut ::core::ffi::c_char> = args_strings
+        .iter_mut()
+        .map(|arg| arg.as_mut_ptr() as *mut ::core::ffi::c_char)
+        .chain(::core::iter::once(::core::ptr::null_mut()))
+        .collect();
+    let mut vars: Vec<*mut ::core::ffi::c_char> = Vec::new();
+    for (var_name, var_value) in ::std::env::vars() {
+        let var: String = format!("{}={}", var_name, var_value);
+        vars.push(
+            ::std::ffi::CString::new(var)
+                .expect("Failed to convert environment variable into CString.")
+                .into_raw(),
+        );
+    }
+    vars.push(::core::ptr::null_mut());
+    unsafe {
+        ::std::process::exit(main_0(
+            (args_ptrs.len() - 1) as ::core::ffi::c_int,
+            args_ptrs.as_mut_ptr() as *mut *mut ::core::ffi::c_char,
+            vars.as_mut_ptr() as *mut *mut ::core::ffi::c_char,
+        ) as i32)
+    }
+}