add initializer code blocks

src/macros.rs

@@ -1202,6 +1202,21 @@ macro_rules! __init_internal {
         // have been initialized. Therefore we can now dismiss the guards by forgetting them.
         $(::core::mem::forget($guards);)*
     };
+    (init_slot($($use_data:ident)?):
+        @data($data:ident),
+        @slot($slot:ident),
+        @guards($($guards:ident,)*),
+        // arbitrary code block
+        @munch_fields(_: { $($code:tt)* }, $($rest:tt)*),
+    ) => {
+        { $($code)* }
+        $crate::__init_internal!(init_slot($($use_data)?):
+            @data($data),
+            @slot($slot),
+            @guards($($guards,)*),
+            @munch_fields($($rest)*),
+        );
+    };
     (init_slot($use_data:ident): // `use_data` is present, so we use the `data` to init fields.
         @data($data:ident),
         @slot($slot:ident),
@@ -1351,6 +1366,20 @@ macro_rules! __init_internal {
             );
         }
     };
+    (make_initializer:
+        @slot($slot:ident),
+        @type_name($t:path),
+        @munch_fields(_: { $($code:tt)* }, $($rest:tt)*),
+        @acc($($acc:tt)*),
+    ) => {
+        // code blocks are ignored for the initializer check
+        $crate::__init_internal!(make_initializer:
+            @slot($slot),
+            @type_name($t),
+            @munch_fields($($rest)*),
+            @acc($($acc)*),
+        );
+    };
     (make_initializer:
         @slot($slot:ident),
         @type_name($t:path),

tests/ui/compile-fail/init/wrong_generics2.stderr

@@ -12,7 +12,7 @@ help: you might have forgotten to add the struct literal inside the block
  --> src/macros.rs
   |
   ~                 ::core::ptr::write($slot, $t { SomeStruct {
-  |9                    $($acc)*
+  |4                    $($acc)*
   ~                 } });
   |
 

tests/underscore.rs

@@ -0,0 +1,31 @@
+use pin_init::{try_init, Init};
+
+pub struct Foo {
+    x: u64,
+}
+
+fn foo() -> bool {
+    false
+}
+
+fn bar() -> bool {
+    true
+}
+
+impl Foo {
+    pub fn new() -> impl Init<Self, ()> {
+        try_init!(Self {
+            _: {
+                if foo() {
+                    return Err(());
+                }
+            },
+            x: 0,
+            _: {
+                if bar() {
+                    return Err(());
+                }
+            }
+        }? ())
+    }
+}