Better PHP7 support, more diagnostics, less false positives

The PHP7 support is still incomplete, but we're getting closer to fix that.

NoVerify works well in self-contained codebases that have all dependencies under their source root. It also requires all types to be resolvable and reports most usages of mixed-typed values as errors. We aware that it could be too strict for many users, perhaps there will be a flag that makes NoVerify more tolerant of untyped code in the future.

Feedback is appreciated.

How to get started

1. Download a binary for your platform.
2. Run NoVerify over your PHP project with noverify ./src/.

Try to avoid running NoVerify over a code that can include definition duplicates. It complicates running analysis over tests, but we're working on making this limitation go away.

More usage info: docs/linter-usage.md.

To list supported diagnostics run noverify --help. Example output:

Diagnostics (checks):
  accessLevel
    	Report erroneous member access.
  argCount
    	Report mismatching args count inside call expressions.
  arrayAccess
    	Report array access to non-array objects.
(+ more lines)

Recent changes

New checkers:

• regexpSimplify tells how to simplify patterns
• regexpVet finds suspicious pattern parts
• regexpSyntax reports syntax errors in patterns
• newAbstract forbids using abstract classes in new expressions
• nameCase requires the same spelling of classes and functions at definitions and usages
• unimplemented reports unimplemented interface/abstract methods
• misspell finds common misspellings in comments and some identifiers
• discardExpr reports "evaluated but not used" expressions
• voidResultUsed reports usage of void-typed expressions

Improvements:

• For simple use cases there is no need to set -cache now
• Linter now understand traits better
• isset/instanceof inside ternary expression condition is now respected (#288)
• Linter now collects info from @method and @property annotations
• Nullable types ?T are now supported
• function_exists() and method_exists() permit calling tested symbol inside if body
• Several improvements to a types inference
• UNUSED severity level is not used in non-LSP mode (#397)
• Case-insensitive symbols handling is improved

Performance:

• Directory traversal speed is increased significantly (#333)
• Lexing became 5-10% faster due to golex -> Ragel switch (#381)

Bug fixes:

• PHP7 style nowdoc/heredoc are now parsed correctly (#327)

Documentation:

• Added Finding the false-positive document