commit 6945a72009a573062e4815ab3d984a17124d553e
author Paul Berry <paulberry@google.com> Tue Sep 27 13:16:33 2022 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Sep 27 13:16:33 2022 +0000
tree 47d0468d926e6afe87c9a1b6bbfdc2170ca1b9dd
parent d7e130e930e2dceba30df421b7042822bc26468e

Patterns: initial parser support.

The parser now supports the following subset of the parser grammar:

- logical-or and logical-and patterns (called "binary patterns" to
  reflect analyzer nomenclature)

- extractor patterns

- cast patterns

- list patterns

- map patterns

- null-assert patterns

- null-check patterns

- variable patterns where the variable is preceded by `var`, `final`,
  <type>, or `final <type>`

- if-case statements (and if-case within collections); without guards

- record patterns

- parenthesized patterns

- constant patterns where the constant is a plain expression not
  beginning with `const` (booleanLiteral, nullLiteral, numericLiteral,
  stringLiteral, identifier, or qualifiedName).

- relational patterns

- patterns in switch statements

- integration with the analyzer's AstBuilder class

Not implemented yet:

- constant patterns beginning with `const`

- variable patterns where the variable is a single identifier (note:
  this means that `_` is currently interpreted as a constant pattern
  rather than a "wildcard" variable pattern)

- guards (a.k.a. "when clauses")

- switch expressions

- pattern variable declarations

- patterns appearing in "for loop parts"

- pattern assignment

- several error checking and error recovery scenarios (see TODO
  comments)

- integration with the front_end's BodyBuilder class

- front_end style parser tests (currently the feature is tested using
  analyzer unit tests only)

Note that in patterns, `as` binds has higher precedence than `&` and
`|`, whereas in expressions, `&` and `|` have higher precedence than
`as`.  To reflect this, a new precedence has been added,
CAST_PATTERN_PRECEDENCE.

To reduce the risk to users during parser development, the parser
currently only attempts to parse patterns when instructed to do so
(i.e. when the language feature is enabled).  In the long term, I
intend to change the parser so that it always attempts to parse
patterns, and it is the responsibility of its listener to report
errors if patterns are used without enabling the language feature.

Change-Id: I360b535d2a6ebd35a0ee4d066b06e3ae8e3121ef
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/261020
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>