karvozavr / ast-info-plugin

AST Info plugin

Author - Dmitrii Abramov.

This plugin shows AST of selected code fragment and following statistics:

• Number of variable declarations inside selection
• Number of read variable accesses in selection
• Number of exceptions which may be thrown during execution of selected fragment

Usage

The easiest way to run the plugin is:
./gradlew runIde

To display AST and info for selection:

1. Select some code in editor.
2. Press AST Info button under AST Info menu-bar entry.
3. Tool Window with AST and statistics will appear.
4. To see info for another code fragment: GOTO 1.

Implementation Details

Plugin uses ToolWindow from Intellij API to present it's UI.

Internal Intellij AST representation - PSI (Program Structure Interface) is used to present tree structure in plugin.

AST by selection

Algorithm:

• Retrieve nodes of AST which correspond to begin and end of the selection.
• Find lowest common ancestor for begin and end node.
• If all ancestor children intersect with selection, return the subtree with root in ancestor.
• Otherwise the list of subtrees with roots in each ancestor child which intersects with the selection is returned.

Statistics by selection

Considering variable as local variable or field.

Declarations

Visiting all nodes in AST corresponding to selection and counting all variable and field declaration nodes.

Usages

Visiting all nodes in AST corresponding to selection and counting all Reference Expression nodes which are read access (i.e. this reference is not on the left of assignment operator).

Exceptions

Here I reused functionality of Intellij API (method com.intellij.codeInsight.ExceptionUtil::getThrownExceptions).

It traverses AST and processes all function calls and gets all exceptions from their function declaration throws list.

Also it processes all throw expressions and try statements (for try statement it correctly doesn't count exceptions which are catch by catch close).