JS: Emit variables for 'this'

[asgerf]

Makes the JS extractor treat this as a variable. That is:

• A variable entity is generated for each scope that introduces this (top-levels, classes, and non-arrow functions).
• ThisExpr is bound to the corresponding variable entity.

The upgrade script however does not implement scoping rules (and declares partial compatibility), but the QL side of things do not make use of these new bindings yet. The idea is to merge the extractor changes well in advance of the corresponding QL changes, so we avoid disruptions caused by the incompatibility change.

[Copilot]

Pull request overview

Updates the JavaScript extractor to model this as a variable and bind ThisExpression occurrences to the corresponding scope-specific this variable, with accompanying TRAP expectation updates and a partial-compat downgrade note.

Changes:

• Emit a this variable for top-level, class, and non-arrow-function scopes in the extractor.
• Bind ThisExpression nodes to the appropriate this variable entity.
• Update many JS extractor TRAP outputs and add a partial-compat upgrade descriptor.

Reviewed changes

Copilot reviewed 78 out of 278 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java	Emit this variables in relevant scopes and bind ThisExpression to them.
javascript/downgrades/26a123164be893893e2aa0374d820785decf55af/upgrade.properties	Declares partial compatibility for the downgrade/upgrade step.
javascript/extractor/tests/es2015/output/trap/super_ctor.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/spreadelement.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/restparms.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/property_pattern_with_default.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/odasa-2593.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/no-substitution.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/new_target.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/let2.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import7.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import6.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import5.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import4.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import3.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import2.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/import1.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export9.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export8.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export7.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export6.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export5.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export4.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export3.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export2.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export11.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export10.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/export1.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/delegating_yield.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/defaultargs.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/const.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/complex_object_pattern.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/complex_array_pattern.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/classexpr2.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/classexpr.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/classdecl.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/class_extends.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/array_pattern_with_rest.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/es2015/output/trap/array_pattern_with_default.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/errors/output/trap/kwident.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/errors/output/trap/invalid-assignment-pattern.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/errors/output/trap/empty.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/encoding/output/trap/unicode.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/e4x/output/trap/regress.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/default-encoding/output/trap/latin1.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/comments/output/trap/jsdoc.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/comments/output/trap/empty_comment.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/comments/output/trap/comments.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/closure/output/trap/googDotDeclareModuleId.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/cfg/output/trap/seq.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/cfg/output/trap/classexpr3.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/cfg/output/trap/classexpr2.js.trap	Updates expected TRAP output to include emitted this variables.
javascript/extractor/tests/cfg/output/trap/classexpr1.js.trap	Updates expected TRAP output to include emitted this variables.

Comments suppressed due to low confidence (5)

javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java:1549

• Typo in comment: 'initialiers' should be 'initializers'.

      scopeManager.addVariables("this"); // 'this' in static field initialiers refers to the class

javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java:822

• The string literal "this" is repeated across multiple sites for both declaration and binding. Consider centralizing it as a constant (e.g., a private static final String THIS_NAME = \"this\";) to reduce duplication and avoid future inconsistencies (especially if related logic later expands to special-casing).

      scopeManager.addVariables("this");

javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java:1076

• The string literal "this" is repeated across multiple sites for both declaration and binding. Consider centralizing it as a constant (e.g., a private static final String THIS_NAME = \"this\";) to reduce duplication and avoid future inconsistencies (especially if related logic later expands to special-casing).

      if (!(nd instanceof ArrowFunctionExpression)) {
        scopeManager.addVariables("this");
      }

javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java:1549

• The string literal "this" is repeated across multiple sites for both declaration and binding. Consider centralizing it as a constant (e.g., a private static final String THIS_NAME = \"this\";) to reduce duplication and avoid future inconsistencies (especially if related logic later expands to special-casing).

      scopeManager.addVariables("this"); // 'this' in static field initialiers refers to the class

javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java:1903

• The string literal "this" is repeated across multiple sites for both declaration and binding. Consider centralizing it as a constant (e.g., a private static final String THIS_NAME = \"this\";) to reduce duplication and avoid future inconsistencies (especially if related logic later expands to special-casing).

        addVariableBinding("bind", key, "this");

[Copilot]

The PR adds binding emission for ThisExpression, but the updated TRAP fixtures in this diff mostly show only the new variables(..., \"this\", ...) entries, not an actual bind relation for a this occurrence. Add at least one extractor test input that contains this usages (e.g., top-level this, non-arrow function this, arrow capturing outer this, and class static field/block this) and assert the resulting TRAP includes the expected bind fact(s) pointing at the correct scope-specific this variable.

Suggested change

	if (c.idcontext == IdContext.VAR_BIND || c.idcontext == IdContext.VAR_IN_TYPE_BIND) {
	addVariableBinding("bind", key, "this");
	}
	return key;
	}
	@Override
	public Label visit(JSXMemberExpression nd, Context c) {
	addVariableBinding("bind", key, "this");
	return key;
	}
	@Override
	public Label visit(JSXMemberExpression nd, Context c) {
	public Label visit(JSXMemberExpression nd, Context c) {

[Napalys]

Looks good to me 👍