Sema: add "cannot convert to payload type" error notes

src/Sema.zig

@@ -2749,7 +2749,15 @@ fn ensureResultUsed(
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag()) {
         .Void, .NoReturn => return,
-        .ErrorSet, .ErrorUnion => return sema.fail(block, src, "error is ignored. consider using `try`, `catch`, or `if`", .{}),
+        .ErrorSet, .ErrorUnion => {
+            const msg = msg: {
+                const msg = try sema.errMsg(block, src, "error is ignored", .{});
+                errdefer msg.destroy(sema.gpa);
+                try sema.errNote(block, src, msg, "consider using `try`, `catch`, or `if`", .{});
+                break :msg msg;
+            };
+            return sema.failWithOwnedErrorMsg(block, msg);
+        },
         else => return sema.fail(block, src, "expression value is ignored", .{}),
     }
 }
@@ -2763,7 +2771,15 @@ fn zirEnsureResultNonError(sema: *Sema, block: *Block, inst: Zir.Inst.Index) Com
     const src = inst_data.src();
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag()) {
-        .ErrorSet, .ErrorUnion => return sema.fail(block, src, "error is discarded. consider using `try`, `catch`, or `if`", .{}),
+        .ErrorSet, .ErrorUnion => {
+            const msg = msg: {
+                const msg = try sema.errMsg(block, src, "error is discarded", .{});
+                errdefer msg.destroy(sema.gpa);
+                try sema.errNote(block, src, msg, "consider using `try`, `catch`, or `if`", .{});
+                break :msg msg;
+            };
+            return sema.failWithOwnedErrorMsg(block, msg);
+        },
         else => return,
     }
 }
@@ -20402,6 +20418,23 @@ fn coerceExtra(
         const msg = try sema.errMsg(block, inst_src, "expected type '{}', found '{}'", .{ dest_ty.fmt(sema.mod), inst_ty.fmt(sema.mod) });
         errdefer msg.destroy(sema.gpa);
 
+        // E!T to T
+        if (inst_ty.zigTypeTag() == .ErrorUnion and
+            (try sema.coerceInMemoryAllowed(block, inst_ty.errorUnionPayload(), dest_ty, false, target, dest_ty_src, inst_src)) == .ok)
+        {
+            try sema.errNote(block, inst_src, msg, "cannot convert error union to payload type", .{});
+            try sema.errNote(block, inst_src, msg, "consider using `try`, `catch`, or `if`", .{});
+        }
+
+        // ?T to T
+        var buf: Type.Payload.ElemType = undefined;
+        if (inst_ty.zigTypeTag() == .Optional and
+            (try sema.coerceInMemoryAllowed(block, inst_ty.optionalChild(&buf), dest_ty, false, target, dest_ty_src, inst_src)) == .ok)
+        {
+            try sema.errNote(block, inst_src, msg, "cannot convert optional to payload type", .{});
+            try sema.errNote(block, inst_src, msg, "consider using `.?`, `orelse`, or `if`", .{});
+        }
+
         try in_memory_result.report(sema, block, inst_src, msg);
         break :msg msg;
     };

test/cases/compile_errors/assigning_to_struct_or_union_fields_that_are_not_optionals_with_a_function_that_returns_an_optional.zig

@@ -15,7 +15,9 @@ export fn entry() void {
 }
 
 // error
-// backend=stage1
+// backend=stage2
 // target=native
 //
-// tmp.zig:11:27: error: cannot convert optional to payload type. consider using `.?`, `orelse`, or `if`. expected type 'u8', found '?u8'
+// :11:27: error: expected type 'u8', found '?u8'
+// :11:27: note: cannot convert optional to payload type
+// :11:27: note: consider using `.?`, `orelse`, or `if`

test/cases/compile_errors/discarding_error_value.zig

@@ -9,4 +9,5 @@ fn foo() !void {
 // backend=stage2
 // target=native
 //
-// :2:12: error: error is discarded. consider using `try`, `catch`, or `if`
+// :2:12: error: error is discarded
+// :2:12: note: consider using `try`, `catch`, or `if`

test/cases/compile_errors/ignored_deferred_function_call.zig

@@ -7,4 +7,5 @@ fn bar() anyerror!i32 { return 0; }
 // backend=stage2
 // target=native
 //
-// :2:14: error: error is ignored. consider using `try`, `catch`, or `if`
+// :2:14: error: error is ignored
+// :2:14: note: consider using `try`, `catch`, or `if`

test/cases/compile_errors/ignored_expression_in_while_continuation.zig

@@ -17,6 +17,9 @@ fn bad() anyerror!void {
 // backend=stage2
 // target=native
 //
-// :2:24: error: error is ignored. consider using `try`, `catch`, or `if`
+// :2:24: error: error is ignored
-// :6:25: error: error is ignored. consider using `try`, `catch`, or `if`
+// :2:24: note: consider using `try`, `catch`, or `if`
-// :10:25: error: error is ignored. consider using `try`, `catch`, or `if`
+// :6:25: error: error is ignored
+// :6:25: note: consider using `try`, `catch`, or `if`
+// :10:25: error: error is ignored
+// :10:25: note: consider using `try`, `catch`, or `if`

test/cases/compile_errors/issue_5618_coercion_of_optional_anyopaque_to_anyopaque_must_fail.zig

@@ -0,0 +1,14 @@
+export fn foo() void {
+    var u: ?*anyopaque = null;
+    var v: *anyopaque = undefined;
+    v = u;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :4:9: error: expected type '*anyopaque', found '?*anyopaque'
+// :4:9: note: cannot convert optional to payload type
+// :4:9: note: consider using `.?`, `orelse`, or `if`
+// :4:9: note: '?*anyopaque' could have null values which are illegal in type '*anyopaque'

test/cases/compile_errors/regression_test_2980_base_type_u32_is_not_type_checked_properly_when_assigning_a_value_within_a_struct.zig

@@ -15,7 +15,9 @@ export fn entry() void {
 }
 
 // error
-// backend=stage1
+// backend=stage2
 // target=native
 //
-// tmp.zig:12:25: error: cannot convert error union to payload type. consider using `try`, `catch`, or `if`. expected type 'u32', found '@typeInfo(@typeInfo(@TypeOf(get_uval)).Fn.return_type.?).ErrorUnion.error_set!u32'
+// :12:25: error: expected type 'u32', found '@typeInfo(@typeInfo(@TypeOf(tmp.get_uval)).Fn.return_type.?).ErrorUnion.error_set!u32'
+// :12:25: note: cannot convert error union to payload type
+// :12:25: note: consider using `try`, `catch`, or `if`

test/cases/compile_errors/result_location_incompatibility_mismatching_handle_is_ptr.zig

@@ -12,7 +12,9 @@ pub const Container = struct {
 };
 
 // error
-// backend=stage1
+// backend=stage2
 // target=native
 //
-// tmp.zig:3:36: error: cannot convert optional to payload type. consider using `.?`, `orelse`, or `if`. expected type 'i32', found '?i32'
+// :3:36: error: expected type 'i32', found '?i32'
+// :3:36: note: cannot convert optional to payload type
+// :3:36: note: consider using `.?`, `orelse`, or `if`

test/cases/compile_errors/result_location_incompatibility_mismatching_handle_is_ptr_generic_call.zig

@@ -12,7 +12,9 @@ pub const Container = struct {
 };
 
 // error
-// backend=stage1
+// backend=stage2
 // target=native
 //
-// tmp.zig:3:36: error: cannot convert optional to payload type. consider using `.?`, `orelse`, or `if`. expected type 'i32', found '?i32'
+// :3:36: error: expected type 'i32', found '?i32'
+// :3:36: note: cannot convert optional to payload type
+// :3:36: note: consider using `.?`, `orelse`, or `if`

test/cases/compile_errors/stage1/obj/issue_5618_coercion_of_optional_anyopaque_to_anyopaque_must_fail.zig

@@ -1,11 +0,0 @@
-export fn foo() void {
-    var u: ?*anyopaque = null;
-    var v: *anyopaque = undefined;
-    v = u;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:4:9: error: cannot convert optional to payload type. consider using `.?`, `orelse`, or `if`. expected type '*anyopaque', found '?*anyopaque'