Add compile error for @ptrCast from 0-bit pointer to non-0-bit pointer

Fixes #1469

Author: tadeokondrak

src/ir.cpp

@@ -29460,6 +29460,20 @@ static IrInstGen *ir_analyze_ptr_cast(IrAnalyze *ira, IrInst* source_instr, IrIn
         return ira->codegen->invalid_inst_gen;
     }
 
+    if (safety_check_on &&
+        !type_has_bits(ira->codegen, dest_type) &&
+        type_has_bits(ira->codegen, if_slice_ptr_type))
+    {
+        ErrorMsg *msg = ir_add_error(ira, source_instr,
+            buf_sprintf("'%s' and '%s' do not have the same in-memory representation",
+                buf_ptr(&src_type->name), buf_ptr(&dest_type->name)));
+        add_error_note(ira->codegen, msg, ptr_src->source_node,
+                buf_sprintf("'%s' has in-memory bits", buf_ptr(&src_type->name)));
+        add_error_note(ira->codegen, msg, dest_type_src->source_node,
+                buf_sprintf("'%s' has no in-memory bits", buf_ptr(&dest_type->name)));
+        return ira->codegen->invalid_inst_gen;
+    }
+
     // For slices, follow the `ptr` field.
     if (is_slice(src_type)) {
         TypeStructField *ptr_field = src_type->data.structure.fields[slice_ptr_index];

test/compile_errors.zig

@@ -2,6 +2,18 @@ const tests = @import("tests.zig");
 const std = @import("std");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.add("casting non-zero-sized-type pointer to zero-sized-type pointer",
+        \\export fn entry() void {
+        \\    var i = @as(usize, 0);
+        \\    var v = @ptrCast(*void, &i);
+        \\    v.* = {};
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:3:13: error: '*usize' and '*void' do not have the same in-memory representation",
+        "tmp.zig:3:30: note: '*usize' has in-memory bits",
+        "tmp.zig:3:22: note: '*void' has no in-memory bits",
+    });
+
     cases.add("slice sentinel mismatch",
         \\export fn entry() void {
         \\    const y: [:1]const u8 = &[_:2]u8{ 1, 2 };