C: Fix an issue with assigning to unitialized variables at end of blocks

Assigning to an uninitialized variable as the last statement in a
block is almost certainly a type, and if that occurs then the
lift_assign re-write will introduce empty blocks causing this error to
occur. Now when we see such an empty block when converting to A-normal
form we turn it into unit, and emit a warning stating that an empty
block has been found as well as the probable cause (uninitialized
variable).

2 files changed, 14 insertions, 0 deletions

diff --git a/test/c/anf_block.expect b/test/c/anf_block.expect
new file mode 100644
index 00000000..9766475a
--- /dev/null
+++ b/test/c/anf_block.expect
@@ -0,0 +1 @@
+ok
diff --git a/test/c/anf_block.sail b/test/c/anf_block.sail
new file mode 100644
index 00000000..bd26f67a
--- /dev/null
+++ b/test/c/anf_block.sail
@@ -0,0 +1,13 @@
+
+val print = "print_endline" : string -> unit
+
+val main : unit -> unit
+
+function main() = {
+  match () {
+    _ => {
+      TEST = ()
+    }
+  };
+  print("ok")
+}
\ No newline at end of file