Stage1: Add compile error for an empty switch on a integer

src/range_set.cpp

@@ -40,6 +40,9 @@ void rangeset_sort(RangeSet *rs) {
 }
 
 bool rangeset_spans(RangeSet *rs, BigInt *first, BigInt *last) {
+    if (rs->src_range_list.length == 0)
+        return false;
+
     rangeset_sort(rs);
 
     const Range *first_range = &rs->src_range_list.at(0).range;

test/compile_errors.zig

@@ -2,6 +2,16 @@ const tests = @import("tests.zig");
 const builtin = @import("builtin");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.add(
+        "empty switch on an integer",
+        \\export fn entry() void {
+        \\    var x: u32 = 0;
+        \\    switch(x) {}
+        \\}
+    ,
+        "tmp.zig:3:5: error: switch must handle all possibilities",
+    );
+
     cases.add(
         "regression test #2980: base type u32 is not type checked properly when assigning a value within a struct",
         \\const Foo = struct {