compile error tests for implicit C pointer casting

See #1059

src/ir.cpp

@@ -8683,16 +8683,6 @@ static ConstCastOnly types_match_const_cast_only(IrAnalyze *ira, ZigType *wanted
     bool actual_opt_or_ptr = actual_ptr_type != nullptr &&
         (actual_type->id == ZigTypeIdPointer || actual_type->id == ZigTypeIdOptional);
     if (wanted_opt_or_ptr && actual_opt_or_ptr) {
-        bool ok_allows_zero = (wanted_allows_zero &&
-                (actual_allows_zero || wanted_ptr_type->data.pointer.is_const)) ||
-            (!wanted_allows_zero && !actual_allows_zero);
-        if (!ok_allows_zero) {
-            result.id = ConstCastResultIdBadAllowsZero;
-            result.data.bad_allows_zero = allocate_nonzero<ConstCastBadAllowsZero>(1);
-            result.data.bad_allows_zero->wanted_type = wanted_type;
-            result.data.bad_allows_zero->actual_type = actual_type;
-            return result;
-        }
         ConstCastOnly child = types_match_const_cast_only(ira, wanted_ptr_type->data.pointer.child_type,
                 actual_ptr_type->data.pointer.child_type, source_node, !wanted_ptr_type->data.pointer.is_const);
         if (child.id == ConstCastResultIdInvalid)
@@ -8705,6 +8695,16 @@ static ConstCastOnly types_match_const_cast_only(IrAnalyze *ira, ZigType *wanted
             result.data.pointer_mismatch->actual_child = actual_ptr_type->data.pointer.child_type;
             return result;
         }
+        bool ok_allows_zero = (wanted_allows_zero &&
+                (actual_allows_zero || wanted_ptr_type->data.pointer.is_const)) ||
+            (!wanted_allows_zero && !actual_allows_zero);
+        if (!ok_allows_zero) {
+            result.id = ConstCastResultIdBadAllowsZero;
+            result.data.bad_allows_zero = allocate_nonzero<ConstCastBadAllowsZero>(1);
+            result.data.bad_allows_zero->wanted_type = wanted_type;
+            result.data.bad_allows_zero->actual_type = actual_type;
+            return result;
+        }
         if ((err = type_resolve(g, actual_ptr_type->data.pointer.child_type, ResolveStatusAlignmentKnown))) {
             result.id = ConstCastResultIdInvalid;
             return result;
@@ -10846,22 +10846,20 @@ static void report_recursive_error(IrAnalyze *ira, AstNode *source_node, ConstCa
             break;
         }
         case ConstCastResultIdBadAllowsZero: {
-            bool wanted_allows_zero = ptr_allows_addr_zero(cast_result->data.bad_allows_zero->wanted_type);
+            ZigType *wanted_type = cast_result->data.bad_allows_zero->wanted_type;
-            bool actual_allows_zero = ptr_allows_addr_zero(cast_result->data.bad_allows_zero->actual_type);
+            ZigType *actual_type = cast_result->data.bad_allows_zero->actual_type;
-            ZigType *wanted_ptr_type = get_src_ptr_type(cast_result->data.bad_allows_zero->wanted_type);
+            bool wanted_allows_zero = ptr_allows_addr_zero(wanted_type);
-            ZigType *actual_ptr_type = get_src_ptr_type(cast_result->data.bad_allows_zero->actual_type);
+            bool actual_allows_zero = ptr_allows_addr_zero(actual_type);
-            ZigType *wanted_elem_type = wanted_ptr_type->data.pointer.child_type;
-            ZigType *actual_elem_type = actual_ptr_type->data.pointer.child_type;
             if (actual_allows_zero && !wanted_allows_zero) {
                 add_error_note(ira->codegen, parent_msg, source_node,
                         buf_sprintf("'%s' could have null values which are illegal in type '%s'",
-                            buf_ptr(&actual_elem_type->name),
+                            buf_ptr(&actual_type->name),
-                            buf_ptr(&wanted_elem_type->name)));
+                            buf_ptr(&wanted_type->name)));
             } else {
                 add_error_note(ira->codegen, parent_msg, source_node,
                         buf_sprintf("mutable '%s' allows illegal null values stored to type '%s'",
-                            buf_ptr(&cast_result->data.bad_allows_zero->wanted_type->name),
+                            buf_ptr(&wanted_type->name),
-                            buf_ptr(&cast_result->data.bad_allows_zero->actual_type->name)));
+                            buf_ptr(&actual_type->name)));
             }
             break;
         }

test/compile_errors.zig

@@ -1,6 +1,42 @@
 const tests = @import("tests.zig");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.addTest(
+        "implicit cast between C pointer and Zig pointer - bad const/align/child",
+        \\export fn a() void {
+        \\    var x: [*c]u8 = undefined;
+        \\    var y: *align(4) u8 = x;
+        \\}
+        \\export fn b() void {
+        \\    var x: [*c]const u8 = undefined;
+        \\    var y: *u8 = x;
+        \\}
+        \\export fn c() void {
+        \\    var x: [*c]u8 = undefined;
+        \\    var y: *u32 = x;
+        \\}
+        \\export fn d() void {
+        \\    var y: *align(1) u32 = undefined;
+        \\    var x: [*c]u32 = y;
+        \\}
+        \\export fn e() void {
+        \\    var y: *const u8 = undefined;
+        \\    var x: [*c]u8 = y;
+        \\}
+        \\export fn f() void {
+        \\    var y: *u8 = undefined;
+        \\    var x: [*c]u32 = y;
+        \\}
+    ,
+        ".tmp_source.zig:3:27: error: cast increases pointer alignment",
+        ".tmp_source.zig:7:18: error: cast discards const qualifier",
+        ".tmp_source.zig:11:19: error: expected type '*u32', found '[*c]u8'",
+        ".tmp_source.zig:11:19: note: pointer type child 'u8' cannot cast into pointer type child 'u32'",
+        ".tmp_source.zig:15:22: error: cast increases pointer alignment",
+        ".tmp_source.zig:19:21: error: cast discards const qualifier",
+        ".tmp_source.zig:23:22: error: expected type '[*c]u32', found '*u8'",
+    );
+
     cases.addTest(
         "implicit casting null c pointer to zig pointer",
         \\comptime {
@@ -39,6 +75,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\}
     ,
         ".tmp_source.zig:6:24: error: expected type '*const [*]const u8', found '[*c]const [*c]const u8'",
+        ".tmp_source.zig:6:24: note: pointer type child '[*c]const u8' cannot cast into pointer type child '[*]const u8'",
         ".tmp_source.zig:6:24: note: '[*c]const u8' could have null values which are illegal in type '[*]const u8'",
         ".tmp_source.zig:13:35: error: expected type '[*c]const [*c]u8', found '*[*]u8'",
         ".tmp_source.zig:13:35: note: pointer type child '[*]u8' cannot cast into pointer type child '[*c]u8'",