lang

Documentation

Overview

Package lang parses failure association rule predicates. The predicate syntax defined here is intended to be a subset of BigQuery Standard SQL's Expression syntax, with the same semantics. This provides a few benefits:

• Well-known and understood syntax and semantics.
• Ability to leverage existing high-quality documentation to communicate language concepts to end-users.
• Simplified debugging of LUCI Analysis (by allowing direct copy- paste of expressions into BigQuery to verify clustering is correct).
• Possibility of using BigQuery as an execution engine in future.

Rules permitted by this package look similar to:

reason LIKE "% exited with code 5 %" AND NOT
  ( test = "arc.Boot" OR test = "arc.StartStop" )

The grammar for the language in Extended Backus-Naur form follows. The top-level production rule is BoolExpr.

BoolExpr = BoolTerm , ( "OR" , BoolTerm )* ; BoolTerm = BoolFactor , ( "AND" , BoolFactor )* ; BoolFactor = [ "NOT" ] BoolPrimary ; BoolPrimary = BoolItem | BoolPredicate ; BoolItem = BoolConst | "(" , BoolExpr , ")" | BoolFunc ; BoolConst = "TRUE" | "FALSE" ; BoolFunc = Identifier , "(" , StringExpr , ( "," , StringExpr )* , ")" ; BoolPredicate = StringExpr , BoolTest ; BoolTest = CompPredicate | NegatablePredicate ; CompPredicate = Operator , StringExpr ; Operator = "!=" | "<>" | "=" NegatablePredicate = [ "NOT" ] , ( InPredicate | LikePredicate ) ; InPredicate = "IN" , "(" , StringExpr , ( "," , StringExpr )* , ")" ; LikePredicate = "LIKE" , String ; StringExpr = String | Identifier ;

Where: - Identifier represents the production rule for identifiers. - String is the production rule for a double-quoted string literal. The precise definitions of which are omitted here but found in the implementation.

Index

• func Merge(rule1 string, rule2 string) (string, error)
• func ValidateLikePattern(likePattern string) error
• type Expr
  • func Parse(text string) (*Expr, error)
  • func (e *Expr) Evaluate(failure *clustering.Failure) bool
  • func (e *Expr) String() string

Functions

func Merge

func Merge(rule1 string, rule2 string) (string, error)

Merge merges two failure association rules with a logical "OR".

func ValidateLikePattern

func ValidateLikePattern(likePattern string) error

ValidateLikePattern validates the given string is a valid LIKE pattern. In particular, this checks that all escape sequences are valid, and that there is no unfinished trailing escape sequence (trailing '\').

Types

type Expr

type Expr struct {
	// contains filtered or unexported fields
}

Expr represents a predicate for a failure association rule.

func Parse

func Parse(text string) (*Expr, error)

Parse parses a failure association rule from the specified text. idents is the set of identifiers that are recognised by the application.

func (*Expr) Evaluate

func (e *Expr) Evaluate(failure *clustering.Failure) bool

Evaluate evaluates the given expression, using the given values for variables used in the expression.

func (*Expr) String

func (e *Expr) String() string

String returns the predicate as a string, with normalised formatting.