Package com.google.javascript.jscomp.lint

Class CheckUselessBlocks

java.lang.Object

com.google.javascript.jscomp.lint.CheckUselessBlocks

All Implemented Interfaces:

CompilerPass, NodeTraversal.Callback

public final class CheckUselessBlocks
extends Object
implements NodeTraversal.Callback, CompilerPass

Check for useless blocks. A block is considered useful if it is part of a control structure like if / else / while / switch / etc. or if it contains any block-scoped variables (let, const, class, or function declarations). Otherwise there is no reason to use it so it is likely a mistake. This would catch the classic error:

return {foo: 'bar'};

or more contrived cases like:

if (denied) { showAccessDenied(); } { grantAccess(); }

Inspired by ESLint (https://github.com/eslint/eslint/blob/master/lib/rules/no-lone-blocks.js)

Field Summary

Fields

Modifier and Type	Field	Description
static final DiagnosticType	USELESS_BLOCK

Constructor Summary

Constructors

Constructor	Description
CheckUselessBlocks(AbstractCompiler compiler)

Method Summary

Modifier and Type	Method	Description
void	process(Node externs, Node root)	Process the JS with root node root.
final boolean	shouldTraverse(NodeTraversal t, Node n, Node parent)	Visits a node in preorder (before its children) and decides whether the node and its children should be traversed.
void	visit(NodeTraversal t, Node n, Node parent)	Visits a node in postorder (after its children).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

USELESS_BLOCK

public static final DiagnosticType USELESS_BLOCK

Constructor Details

CheckUselessBlocks

public CheckUselessBlocks(AbstractCompiler compiler)

Method Details

process

public void process(Node externs,
 Node root)

Description copied from interface: CompilerPass

Process the JS with root node root. Can modify the contents of each Node tree

Specified by:

process in interface CompilerPass

Parameters:

externs - Top of external JS tree

root - Top of JS tree

shouldTraverse

public final boolean shouldTraverse(NodeTraversal t,
 Node n,
 Node parent)

Description copied from interface: NodeTraversal.Callback

Visits a node in preorder (before its children) and decides whether the node and its children should be traversed.

If this method returns true, the node will be visited by NodeTraversal.Callback.visit(NodeTraversal, Node, Node) in postorder and its children will be visited by both NodeTraversal.Callback.shouldTraverse(NodeTraversal, Node, Node) in preorder and by NodeTraversal.Callback.visit(NodeTraversal, Node, Node) in postorder.

If this method returns false, the node will not be visited by NodeTraversal.Callback.visit(NodeTraversal, Node, Node) and its children will neither be visited by NodeTraversal.Callback.shouldTraverse(NodeTraversal, Node, Node) nor NodeTraversal.Callback.visit(NodeTraversal, Node, Node).

Siblings are always visited left-to-right.

Implementations can have side-effects (e.g. modify the parse tree). Removing the current node is legal, but removing or reordering nodes above the current node may cause nodes to be visited twice or not at all.

Specified by:

shouldTraverse in interface NodeTraversal.Callback

Parameters:

t - The current traversal.

n - The current node.

parent - The parent of the current node.

Returns:

whether the children of this node should be visited

visit

public void visit(NodeTraversal t,
 Node n,
 Node parent)

Description copied from interface: NodeTraversal.Callback

Visits a node in postorder (after its children). A node is visited in postorder iff NodeTraversal.Callback.shouldTraverse(NodeTraversal, Node, Node) returned true for its parent and itself. In particular, the root node is never visited in postorder.

Siblings are always visited left-to-right.

Implementations can have side-effects (e.g. modify the parse tree). Removing the current node is legal, but removing or reordering nodes above the current node may cause nodes to be visited twice or not at all.

Specified by:

visit in interface NodeTraversal.Callback

Parameters:

t - The current traversal.

n - The current node.

parent - The parent of the current node.