gccrs: allow casts from numeric types to floats

Fixes #3261

gcc/rust/ChangeLog:

	* typecheck/rust-casts.cc (TypeCastRules::cast_rules): allow casts to float

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3261.rs: New test.

Signed-off-by: Philip Herron <[email protected]>

gcc/rust/typecheck/rust-casts.cc

@@ -200,6 +200,16 @@ TypeCastRules::cast_rules ()
 	  }
 	  break;
 
+	  case TyTy::TypeKind::FLOAT: {
+	    // can only do this for number types not char
+	    bool from_char
+	      = from.get_ty ()->get_kind () == TyTy::TypeKind::CHAR;
+	    if (!from_char)
+	      return TypeCoercionRules::CoercionResult{{},
+						       to.get_ty ()->clone ()};
+	  }
+	  break;
+
 	case TyTy::TypeKind::INFER:
 	case TyTy::TypeKind::USIZE:
 	case TyTy::TypeKind::ISIZE:

gcc/testsuite/rust/compile/issue-3261.rs

@@ -0,0 +1,18 @@
+// { dg-options "-w" }
+fn main() {
+    let a: i8 = 50;
+    let b = a as f32;
+    let c = a as f64;
+
+    let a: i16 = 1337;
+    let b = a as f32;
+    let c = a as f64;
+
+    let a: i32 = 1337;
+    let b = a as f32;
+    let c = a as f64;
+
+    let a: i64 = 1337;
+    let b = a as f32;
+    let c = a as f64;
+}