ptrCast builtin now gives an error for removing const qualifier

closes #384

src/analyze.cpp

@@ -3753,6 +3753,19 @@ uint32_t get_ptr_align(TypeTableEntry *type) {
     }
 }
 
+bool get_ptr_const(TypeTableEntry *type) {
+    TypeTableEntry *ptr_type = get_codegen_ptr_type(type);
+    if (ptr_type->id == TypeTableEntryIdPointer) {
+        return ptr_type->data.pointer.is_const;
+    } else if (ptr_type->id == TypeTableEntryIdFn) {
+        return true;
+    } else if (ptr_type->id == TypeTableEntryIdPromise) {
+        return true;
+    } else {
+        zig_unreachable();
+    }
+}
+
 AstNode *get_param_decl_node(FnTableEntry *fn_entry, size_t index) {
     if (fn_entry->param_source_nodes)
         return fn_entry->param_source_nodes[index];

src/analyze.hpp

@@ -55,6 +55,7 @@ bool type_is_codegen_pointer(TypeTableEntry *type);
 
 TypeTableEntry *get_codegen_ptr_type(TypeTableEntry *type);
 uint32_t get_ptr_align(TypeTableEntry *type);
+bool get_ptr_const(TypeTableEntry *type);
 TypeTableEntry *validate_var_type(CodeGen *g, AstNode *source_node, TypeTableEntry *type_entry);
 TypeTableEntry *container_ref_type(TypeTableEntry *type_entry);
 bool type_is_complete(TypeTableEntry *type_entry);

src/ir.cpp

@@ -16816,6 +16816,11 @@ static TypeTableEntry *ir_analyze_instruction_ptr_cast(IrAnalyze *ira, IrInstruc
         return ira->codegen->builtin_types.entry_invalid;
     }
 
+    if (get_ptr_const(src_type) && !get_ptr_const(dest_type)) {
+        ir_add_error(ira, &instruction->base, buf_sprintf("cast discards const qualifier"));
+        return ira->codegen->builtin_types.entry_invalid;
+    }
+
     if (instr_is_comptime(ptr)) {
         ConstExprValue *val = ir_resolve_const(ira, ptr, UndefOk);
         if (!val)

std/buf_map.zig

@@ -62,9 +62,7 @@ pub const BufMap = struct {
     }
 
     fn free(self: &BufMap, value: []const u8) void {
-        // remove the const
+        self.hash_map.allocator.free(value);
-        const mut_value = @ptrCast(&u8, value.ptr)[0..value.len];
-        self.hash_map.allocator.free(mut_value);
     }
 
     fn copy(self: &BufMap, value: []const u8) ![]const u8 {

std/buf_set.zig

@@ -50,9 +50,7 @@ pub const BufSet = struct {
     }
 
     fn free(self: &BufSet, value: []const u8) void {
-        // remove the const
+        self.hash_map.allocator.free(value);
-        const mut_value = @ptrCast(&u8, value.ptr)[0..value.len];
-        self.hash_map.allocator.free(mut_value);
     }
 
     fn copy(self: &BufSet, value: []const u8) ![]const u8 {

std/os/index.zig

@@ -1634,7 +1634,7 @@ pub fn argsFree(allocator: &mem.Allocator, args_alloc: []const []u8) void {
     for (args_alloc) |arg| {
         total_bytes += @sizeOf([]u8) + arg.len;
     }
-    const unaligned_allocated_buf = @ptrCast(&u8, args_alloc.ptr)[0..total_bytes];
+    const unaligned_allocated_buf = @ptrCast(&const u8, args_alloc.ptr)[0..total_bytes];
     const aligned_allocated_buf = @alignCast(@alignOf([]u8), unaligned_allocated_buf);
     return allocator.free(aligned_allocated_buf);
 }

std/special/compiler_rt/udivmod.zig

@@ -11,8 +11,8 @@ pub fn udivmod(comptime DoubleInt: type, a: DoubleInt, b: DoubleInt, maybe_rem:
     const SignedDoubleInt = @IntType(true, DoubleInt.bit_count);
     const Log2SingleInt = @import("../../math/index.zig").Log2Int(SingleInt);
 
-    const n = *@ptrCast(&[2]SingleInt, &a); // TODO issue #421
+    const n = *@ptrCast(&const [2]SingleInt, &a); // TODO issue #421
-    const d = *@ptrCast(&[2]SingleInt, &b); // TODO issue #421
+    const d = *@ptrCast(&const [2]SingleInt, &b); // TODO issue #421
     var q: [2]SingleInt = undefined;
     var r: [2]SingleInt = undefined;
     var sr: c_uint = undefined;

test/cases/cast.zig

@@ -16,7 +16,7 @@ test "integer literal to pointer cast" {
 test "pointer reinterpret const float to int" {
     const float: f64 = 5.99999999999994648725e-01;
     const float_ptr = &float;
-    const int_ptr = @ptrCast(&i32, float_ptr);
+    const int_ptr = @ptrCast(&const i32, float_ptr);
     const int_val = *int_ptr;
     assert(int_val == 858993411);
 }

test/cases/misc.zig

@@ -261,7 +261,7 @@ test "generic malloc free" {
     const a = memAlloc(u8, 10) catch unreachable;
     memFree(u8, a);
 }
-const some_mem : [100]u8 = undefined;
+var some_mem : [100]u8 = undefined;
 fn memAlloc(comptime T: type, n: usize) error![]T {
     return @ptrCast(&T, &some_mem[0])[0..n];
 }

test/compile_errors.zig

@@ -1,6 +1,14 @@
 const tests = @import("tests.zig");
 
 pub fn addCases(cases: &tests.CompileErrorContext) void {
+    cases.add("@ptrCast discards const qualifier",
+        \\export fn entry() void {
+        \\    const x: i32 = 1234;
+        \\    const y = @ptrCast(&i32, &x);
+        \\}
+    ,
+        ".tmp_source.zig:3:15: error: cast discards const qualifier");
+
     cases.add("comptime slice of undefined pointer non-zero len",
         \\export fn entry() void {
         \\    const slice = (&i32)(undefined)[0..1];