Symbols create a tooling gap

[sethladd]

Symbols are often used to refer to fields or classes. Currently, the tools aren't able to give good feedback or assistance when symbols are used. e.g. if a symbol that is meant to refer to a field name, the tools have no way to detect if the symbol was misspelled, and no way to help refactor-rename.

We now have symbols, which are often used to represent names in Dart code, I'm concerned we're losing some tooling ability.

e.g. this is common in Polymer.dart code:

    bindProperty(this, const Symbol('timestamp'),
        () => notifyProperty(this, const Symbol('second')));

The first symbol is the name of a field, the second symbol is the name of a getter. If I rename my field, the symbol is left untouched. And if I misspell the symbol name...

This lies at the intersection of tooling, API design, and maybe language. Do you think we can do better here? Should the API be changed or should the tools help here?

[anders-sandholm]

Added Area-Tools label.

[DartBot]

This comment was originally written by @seaneagan

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mailing list discussion:

https://groups.google.com/a/dartlang.org/d/msg/misc/a0Fk1XSn6Fc/1DJvkLIkjc4J

Refining some ideas from there:

1. Symbol literal extensions:

symbolLiteral:
  librarySymbolLiteral libraryMemberSymbolLiteral?
| librarySymbolLiteral? classSymbolLiteral classMemberSymbolLiteral?
| classMemberSymbolLiteral

librarySymbolLiteral: ‘#’ identifier (‘.’ identifier)*

classSymbolLiteral: ‘#’ qualified

classMemberSymbolLiteral: ‘#’ operator | (identifier '='?)

libraryMemberSymbolLiteral: ‘#’ identifier '='?

Examples:

#MyClass
#MyClass#myMember
#MyClass#+
#MyClass#staticMethod
#my.lib.name
#my.lib.name#topLevel
#my.lib.name#MyClass#myMember

Dot-less library identifiers could still conflict with class or member identifiers, but at least class identifiers have different naming conventions (UpperCamelCase).

2. More explicit Symbol constructors:

class Symbol {
  const Symbol.fromType(Type type, [Symbol member]);
  const Symbol.fromLibrary(Symbol libraryName, [Symbol member]);
  //...
}

Examples:

const Symbol.fromType(MyClass)
const Symbol.fromType(MyClass, #myMember)
const Symbol.fromType(MyClass, #+)
const Symbol.fromType(MyClass, #staticMethod)
const Symbol.fromLibrary(#my.lib.name)
const Symbol.fromLibrary(#my.lib.name, #topLevel)

which could be improved a tiny bit with first class libraries.

[DartBot]

This comment was originally written by greg.lo...@gmail.com

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I just caught by doing a refactor rename of a field, and forgot to update the name of a symbol in my code. I understand, that it usually will not be possible to rename these automatically as the symbol could refer to any number of methods/getters in the code.

But perhaps the editor could provide a warning if there are symbols with a matching name which may need to be updated.

[sethladd]

Removed Area-Tools label.
Added Area-Editor label.

[DartBot]

This comment was originally written by @zoechi

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I guess https://code.google.com/p/dart/issues/detail?id=15793 could be solved with this one too if Symbol would expose a name property to get the string back from the symbol.

[clayberg]

Set owner to @scheglov.
Added this to the 1.2 milestone.
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Added Priority-Medium label.

[clayberg]

Removed this from the 1.2 milestone.
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[scheglov]

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[kasperl]

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[kasperl]

Removed this from the 1.5 milestone.
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[kasperl]

Removed this from the 1.6 milestone.
Added Oldschool-Milestone-1.6 label.

[sethladd]

Added NotPlanned label.

[DartBot]

This comment was originally written by @Andersmholmgren

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Oh no :-(. How come?

[scheglov]

Removed Area-Editor, Oldschool-Milestone-1.6 labels.
Added Area-Analyzer, Oldschool-Milestone-1.7, Analyzer-Refactoring, Triaged labels.

[sethladd]

Did you mean to set Oldschool-Milestone-7 ?

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Removed Oldschool-Milestone-1.7 label.