add ability to set the errno value

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

perlmod-macro/src/attribs.rs

@@ -129,6 +129,7 @@ pub struct FunctionAttrs {
     pub cv_variable: Option<Ident>,
     pub prototype: Option<String>,
     pub serialize_error: bool,
+    pub errno: bool,
 }
 
 impl TryFrom<AttributeArgs> for FunctionAttrs {
@@ -160,6 +161,8 @@ impl TryFrom<AttributeArgs> for FunctionAttrs {
                         attrs.raw_return = true;
                     } else if path.is_ident("serialize_error") {
                         attrs.serialize_error = true;
+                    } else if path.is_ident("errno") {
+                        attrs.errno = true;
                     } else {
                         error!(path => "unknown attribute");
                     }

perlmod-macro/src/function.rs

@@ -368,6 +368,12 @@ fn handle_return_kind(
         TokenStream::new()
     };
 
+    let copy_errno = if attr.errno {
+        quote! { ::perlmod::error::copy_errno_to_libc(); }
+    } else {
+        TokenStream::new()
+    };
+
     let pthx = crate::pthx_param();
     match ret.value {
         ReturnValue::None => {
@@ -398,7 +404,9 @@ fn handle_return_kind(
                 #[doc(hidden)]
                 #vis extern "C" fn #xs_name(#pthx #cv_arg_name: *mut ::perlmod::ffi::CV) {
                     unsafe {
-                        match #impl_xs_name(#cv_arg_passed) {
+                        let res = #impl_xs_name(#cv_arg_passed);
+                        #copy_errno
+                        match res {
                             Ok(()) => (),
                             Err(sv) => ::perlmod::ffi::croak(sv),
                         }
@@ -441,7 +449,9 @@ fn handle_return_kind(
                 #[doc(hidden)]
                 #vis extern "C" fn #xs_name(#pthx #cv_arg_name: *mut ::perlmod::ffi::CV) {
                     unsafe {
-                        match #impl_xs_name(#cv_arg_passed) {
+                        let res = #impl_xs_name(#cv_arg_passed);
+                        #copy_errno
+                        match res {
                             Ok(sv) => ::perlmod::ffi::stack_push_raw(sv),
                             Err(sv) => ::perlmod::ffi::croak(sv),
                         }
@@ -523,7 +533,9 @@ fn handle_return_kind(
                 #[doc(hidden)]
                 #vis extern "C" fn #xs_name(#pthx #cv_arg_name: *mut ::perlmod::ffi::CV) {
                     unsafe {
-                        match #impl_xs_name(#cv_arg_passed) {
+                        let res = #impl_xs_name(#cv_arg_passed);
+                        #copy_errno
+                        match res {
                             Ok(sv) => { #push },
                             Err(sv) => ::perlmod::ffi::croak(sv),
                         }

perlmod-test/src/pkg142.rs

@@ -92,7 +92,7 @@ mod export {
         b: String,
     }
 
-    #[export(serialize_error)]
+    #[export(serialize_error, errno)]
     fn test_deserialized_error(fail: bool) -> Result<&'static str, MyError> {
         if fail {
             Err(MyError {
@@ -100,6 +100,7 @@ mod export {
                 b: "second".to_string(),
             })
         } else {
+            ::perlmod::error::set_errno(77);
             Ok("worked")
         }
     }

perlmod/src/error.rs

@@ -1,6 +1,8 @@
 //! Error types.
 
+use std::cell::Cell;
 use std::fmt;
+use std::os::raw::c_int;
 
 /// Error returned by `TryFrom` implementations between `Scalar`, `Array` and `Hash`.
 #[derive(Debug)]
@@ -84,3 +86,30 @@ impl fmt::Display for MagicError {
 }
 
 impl std::error::Error for MagicError {}
+
+thread_local! {
+    static ERRNO: Cell<c_int> = Cell::new(0);
+}
+
+/// Set the perlmod-specific `errno` value. This is *not* libc's `errno`, but a separate storage
+/// location not touched by other C or perl functions. An `#[export(errno)]` function will copy
+/// this value to libc's errno location at right before returning into the perl stack (*after* all
+/// side effects such as destructors have already finished).
+pub fn set_errno(value: c_int) {
+    ERRNO.with(|v| v.set(value))
+}
+
+/// *Not* `libc`'s `errno`, this retrieves a value previously set with [`set_errno`], see its
+/// description for details.
+pub fn get_errno() -> c_int {
+    ERRNO.with(|v| v.get())
+}
+
+/// This is part of the proc-macro API and is of little use to users of this crate directly.
+/// When manually implementing "xsubs" this can be used before returning as a shortcut to copying
+/// the perlmod errno value to libc.
+pub unsafe fn copy_errno_to_libc() {
+    unsafe {
+        libc::__errno_location().write(get_errno());
+    }
+}

test.pl

@@ -122,6 +122,7 @@ my $sub = RSPM::Foo142::test_substr_return($orig);
 print("[$orig] [$sub]\n");
 
 my $ok = RSPM::Foo142::test_deserialized_error(0);
+die "test_deserialized_error failed to set errno value\n" if $! != 77;
 die "test_deserialized_error failed to return a value\n" if $ok ne 'worked';
 $ok = eval { RSPM::Foo142::test_deserialized_error(1) };
 die "test_deserialized_error error case returned a value\n" if defined $ok;