Allowing null pointers is undesirable #24
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This comment was originally written by cf...@gmail.com This is a duplicate of #22, Google Code returned a 502 when I submitted #22 so I didn't see it had gone through. Please delete this copy. |
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This comment was originally written by johnle...@google.com |
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Pulls in: * Added `prefer_is_not_empty` lint rule (#143). * Added `type_annotate_public_apis` lint rule (#24). * Added `avoid_as` lint rule (#145). * Fixed `non_constant_identifier_names` rule to special case underscore identifiers in callbacks. * Fix to escape `_`s in callback type validation (addresses false positives in `always_specify_types`) (#147). R=keertip@google.com Review URL: https://codereview.chromium.org/1434773002 .
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Here's a minimal repro that this CL fixes: `ui.dart` ```dart library dart.ui; import 'dart:ffi'; part 'foo.dart'; ``` `foo.dart` ```dart part of dart.ui; @Native<Void Function()>(symbol: 'foo_func', isLeaf: true) external void foo_func(); ``` When compiling with `compile_platform.dart` with `--target=dart2wasm`, the following error appears: ``` Unhandled exception: Verification error: Target=wasm, VerificationStage.afterModularTransformations: Invalid location with target 'wasm' on FunctionNode() (FunctionNode): RangeError (offset): Invalid value: Not in inclusive range 0..56: 91 Context: 'foo_func_$import'. Node: 'FunctionNode()'. #0 VerificationErrorListener.reportError (package:kernel/verifier.dart:81:5) #1 VerifyingVisitor.problem (package:kernel/verifier.dart:222:14) #2 VerifyingVisitor._getLocation (package:kernel/verifier.dart:1361:7) #3 VerifyingVisitor._hasLocation (package:kernel/verifier.dart:1370:26) #4 VerifyingVisitor.getSameLibraryLastSeenTreeNode (package:kernel/verifier.dart:1342:28) #5 VerifyingVisitor.localContext (package:kernel/verifier.dart:1382:24) #6 VerifyingVisitor.defaultDartType (package:kernel/verifier.dart:1491:41) #7 Visitor.visitVoidType (package:kernel/visitor.dart:1309:37) #8 VoidType.accept (package:kernel/ast.dart:11190:42) #9 FunctionNode.visitChildren (package:kernel/ast.dart:3919:16) #10 VerifyingVisitor.visitChildren (package:kernel/verifier.dart:259:10) #11 VerifyingVisitor.visitWithLocalScope (package:kernel/verifier.dart:266:5) #12 VerifyingVisitor.visitFunctionNode (package:kernel/verifier.dart:721:5) #13 FunctionNode.accept (package:kernel/ast.dart:3908:38) #14 VerifyingVisitor.visitProcedure (package:kernel/verifier.dart:620:19) #15 Procedure.accept (package:kernel/ast.dart:3311:40) #16 visitList (package:kernel/ast.dart:14488:14) #17 Library.visitChildren (package:kernel/ast.dart:591:5) #18 VerifyingVisitor.visitChildren (package:kernel/verifier.dart:259:10) #19 VerifyingVisitor.defaultTreeNode (package:kernel/verifier.dart:196:5) #20 TreeVisitor.visitLibrary (package:kernel/visitor.dart:503:35) #21 VerifyingVisitor.visitLibrary (package:kernel/verifier.dart:367:11) #22 Library.accept (package:kernel/ast.dart:577:38) #23 visitList (package:kernel/ast.dart:14488:14) #24 Component.visitChildren (package:kernel/ast.dart:14320:5) #25 VerifyingVisitor.visitChildren (package:kernel/verifier.dart:259:10) #26 VerifyingVisitor.visitComponent (package:kernel/verifier.dart:342:7) #27 Component.accept (package:kernel/ast.dart:14313:38) #28 VerifyingVisitor.check (package:kernel/verifier.dart:171:15) #29 verifyComponent (package:kernel/verifier.dart:69:20) ... ``` The issue seems to be that after doing this native transformation, the node's `fileUri` references the enclosing library (`ui.dart` above), but the `node.location` references the actual source file (`foo.dart` above) indirectly through `node.fileOffset`. This ends up being an issue when compiling the platform dill in Google3, but I didn't look into why `flutter build web --wasm` isn't broken. Internal bug: b/292172146 Change-Id: I2b8d7d215b2c36354860257ce651d50168e9523d Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/315360 Reviewed-by: Ömer Ağacan <omersa@google.com> Commit-Queue: Jia Hao Goh <jiahaog@google.com>
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This issue was originally filed by cf...@gmail.com
Short version: Null pointers are a really good way to mess up a program at runtime, and I'd like the Dart team to reevaluate whether they're absolutely required.
Slightly longer version: I would say the #1 cause of issues in my programs (excluding logical errors/requirements errors) are NPEs. Having a language support NPE removal, be it via some clever compiler warning or simply removing null altogether, would be wonderful. I'm personally partial to Scala's method of null removal, but I'm sure PL gurus like yourselves have seen many others.
Dart has a stated goal of avoiding the creation of programs that "are difficult to debug or maintain." NPEs are a huge pain point in this regard. I'd be really happy if the Dart team reevaluated whether they are absolutely required to achieve the other aims.
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