add JS support the using keyword

Author: erik-krogh

javascript/extractor/src/com/semmle/jcorn/ESNextParser.java

@@ -51,6 +51,9 @@
 public class ESNextParser extends JSXParser {
   public ESNextParser(Options options, String input, int startPos) {
     super(options.allowImportExportEverywhere(true), input, startPos);
+
+    // recognise `using` as a keyword. See https://github.com/tc39/proposal-explicit-resource-management
+    this.keywords.add("using");
   }
 
   /*

javascript/extractor/src/com/semmle/jcorn/Parser.java

@@ -2737,7 +2737,7 @@ protected Statement parseStatement(boolean declaration, boolean topLevel, Set<St
       return this.parseThrowStatement(startLoc);
     } else if (starttype == TokenType._try) {
       return this.parseTryStatement(startLoc);
-    } else if (starttype == TokenType._const || starttype == TokenType._var) {
+    } else if (starttype == TokenType._const || starttype == TokenType._var || starttype == TokenType._using) {
       if (kind == null) kind = String.valueOf(this.value);
       if (!declaration && !kind.equals("var")) this.unexpected();
       return this.parseVarStatement(startLoc, kind);
@@ -2840,7 +2840,7 @@ protected Statement parseForStatement(Position startLoc) {
     this.expect(TokenType.parenL);
     if (this.type == TokenType.semi) return this.parseFor(startLoc, null);
     boolean isLet = this.isLet();
-    if (this.type == TokenType._var || this.type == TokenType._const || isLet) {
+    if (this.type == TokenType._var || this.type == TokenType._const || isLet || this.type == TokenType._using) { // TODO: Add test for this.
       Position initStartLoc = this.startLoc;
       String kind = isLet ? "let" : String.valueOf(this.value);
       this.next();
@@ -3122,7 +3122,7 @@ protected VariableDeclaration parseVar(Position startLoc, boolean isFor, String
       Expression init = null;
       if (this.eat(TokenType.eq)) {
         init = this.parseMaybeAssign(isFor, null, null);
-      } else if (kind.equals("const")
+      } else if ((kind.equals("const") || kind.equals("using"))
           && !(this.type == TokenType._in
               || (this.options.ecmaVersion() >= 6 && this.isContextual("of")))) {
         this.raiseRecoverable(

javascript/extractor/src/com/semmle/jcorn/TokenType.java

@@ -180,6 +180,7 @@ public void updateContext(Parser parser, TokenType prevType) {
       _try = new TokenType(kw("try")),
       _var = new TokenType(kw("var")),
       _const = new TokenType(kw("const")),
+      _using = new TokenType(kw("using")),
       _while = new TokenType(kw("while").isLoop()),
       _with = new TokenType(kw("with")),
       _new = new TokenType(kw("new").beforeExpr().startsExpr()),

javascript/extractor/src/com/semmle/js/ast/VariableDeclaration.java

@@ -28,8 +28,8 @@ public <Q, A> A accept(Visitor<Q, A> v, Q q) {
   }
 
   /**
-   * The kind of this variable declaration statement; one of <code>"var"</code>, <code>"let"</code>
-   * or <code>"const"</code>.
+   * The kind of this variable declaration statement; one of <code>"var"</code>, <code>"let"</code>,
+   * <code>"const"</code>, or <code>"using"</code>.
    */
   public String getKind() {
     return kind;
@@ -42,6 +42,7 @@ public String getKind() {
    */
   public boolean isBlockScoped(ECMAVersion ecmaVersion) {
     return "let".equals(kind)
+        || "using".equals(kind)
         || ecmaVersion.compareTo(ECMAVersion.ECMA2015) >= 0 && "const".equals(kind);
   }
 

javascript/extractor/src/com/semmle/js/extractor/StmtKinds.java

@@ -58,6 +58,7 @@ public class StmtKinds {
     declKinds.put("var", 18);
     declKinds.put("const", 22);
     declKinds.put("let", 23);
+    declKinds.put("using", 40);
   }
 
   public static int getStmtKind(final Statement stmt) {

javascript/ql/lib/semmle/javascript/PrintAst.qll

@@ -246,13 +246,15 @@ private module PrintJavaScript {
     }
 
     /**
-     * Gets "var" or "const" or "let" depending on what type of declaration `decl` is.
+     * Gets "var" or "const" or "let" or "using" depending on what type of declaration `decl` is.
      */
     private string getDeclarationKeyword(DeclStmt decl) {
       decl instanceof VarDeclStmt and result = "var"
       or
       decl instanceof ConstDeclStmt and result = "const"
       or
+      decl instanceof UsingDeclStmt and result = "using"
+      or
       decl instanceof LetStmt and result = "let"
     }
   }

javascript/ql/lib/semmle/javascript/Stmt.qll

@@ -1041,6 +1041,17 @@ class VarDeclStmt extends @var_decl_stmt, DeclStmt { }
  */
 class ConstDeclStmt extends @const_decl_stmt, DeclStmt { }
 
+/**
+ * A `using` declaration statement.
+ *
+ * Example:
+ *
+ * ```
+ * using file = new TextFile("file.txt");
+ * ```
+ */
+class UsingDeclStmt extends @using_decl_stmt, DeclStmt { }
+
 /**
  * A `let` declaration statement.
  *

javascript/ql/lib/semmlecode.javascript.dbscheme

@@ -162,9 +162,10 @@ case @stmt.kind of
 | 37 = @external_module_declaration
 | 38 = @export_as_namespace_declaration
 | 39 = @global_augmentation_declaration
+| 40 = @using_decl_stmt
 ;
 
-@decl_stmt = @var_decl_stmt | @const_decl_stmt | @let_stmt | @legacy_let_stmt;
+@decl_stmt = @var_decl_stmt | @const_decl_stmt | @let_stmt | @legacy_let_stmt | @using_decl_stmt;
 
 @export_declaration = @export_all_declaration | @export_default_declaration | @export_named_declaration;
 

javascript/ql/src/Declarations/AssignmentToConst.ql

@@ -13,8 +13,9 @@
 import javascript
 import semmle.javascript.RestrictedLocations
 
-from ConstDeclStmt cds, VariableDeclarator decl, VarDef def, Variable v
+from DeclStmt cds, VariableDeclarator decl, VarDef def, Variable v
 where
+  (cds instanceof ConstDeclStmt or cds instanceof UsingDeclStmt) and
   decl = cds.getADecl() and
   def.getAVariable() = v and
   decl.getBindingPattern().getAVariable() = v and

javascript/ql/src/Statements/UselessConditional.ql

@@ -39,6 +39,8 @@ predicate isSymbolicConstant(Variable v) {
   exists(VarDef vd | vd = getSingleDef(v) |
     vd.(VariableDeclarator).getDeclStmt() instanceof ConstDeclStmt
     or
+    vd.(VariableDeclarator).getDeclStmt() instanceof UsingDeclStmt
+    or
     isConstant(vd.getSource())
   )
 }