Merge pull request #519 from esben-semmle/js/nullish-coalescing-extractor-and-ql

JS: nullish coalescing support in extractor and QL

change-notes/1.20/extractor-javascript.md

@@ -0,0 +1,21 @@
+[[ condition: enterprise-only ]]
+
+# Improvements to JavaScript analysis
+
+> NOTES
+>
+> Please describe your changes in terms that are suitable for
+> customers to read. These notes will have only minor tidying up
+> before they are published as part of the release notes.
+>
+> This file is written for lgtm users and should contain *only*
+> notes about changes that affect lgtm enterprise users. Add
+> any other customer-facing changes to the `studio-java.md`
+> file.
+>
+
+## General improvements
+
+## Changes to code extraction
+
+* The extractor now supports [Nullish Coalescing](https://github.com/tc39/proposal-nullish-coalescing) expressions.

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

@@ -508,8 +508,12 @@ public class Parser {
 	private Token readToken_question() { // '?'
 		int next = charAt(this.pos + 1);
 		int next2 = charAt(this.pos + 2);
-		if (this.options.esnext() && next == '.' && !('0' <= next2 && next2 <= '9')) // '?.', but not '?.X' where X is a digit
-			return this.finishOp(TokenType.questiondot, 2);
+		if (this.options.esnext()) {
+			if (next == '.' && !('0' <= next2 && next2 <= '9')) // '?.', but not '?.X' where X is a digit
+				return this.finishOp(TokenType.questiondot, 2);
+			if (next == '?') // '??'
+				return this.finishOp(TokenType.questionquestion, 2);
+		}
 		return this.finishOp(TokenType.question, 1);
 	}
 

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

@@ -123,6 +123,7 @@ public class TokenType {
 		}
 	},
 	prefix = new TokenType(new Properties("prefix").beforeExpr().prefix().startsExpr()),
+	questionquestion = new TokenType(binop("??", 1)),
 	logicalOR = new TokenType(binop("||", 1)),
 	logicalAND = new TokenType(binop("&&", 2)),
 	bitwiseOR = new TokenType(binop("|", 3)),

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

@@ -331,9 +331,11 @@ public class CFGExtractor {
 			return nd.getKey().accept(this, v);
 		}
 
-		// for binary operators, the operands come first (but not for LogicalExpression, see above)
+		// for binary operators, the operands come first (but not for short-circuiting expressions), see above)
 		@Override
 		public Node visit(BinaryExpression nd, Void v) {
+			if ("??".equals(nd.getOperator()))
+				return nd;
 			return nd.getLeft().accept(this, v);
 		}
 
@@ -1583,8 +1585,16 @@ public class CFGExtractor {
 
 		@Override
 		public Void visit(BinaryExpression nd, SuccessorInfo i) {
-			this.seq(nd.getLeft(), nd.getRight(), nd);
-			succ(nd, i.getGuardedSuccessors(nd));
+			if ("??".equals(nd.getOperator())) {
+				// the nullish coalescing operator is short-circuiting, but we do not add guards for it
+				succ(nd, First.of(nd.getLeft()));
+				Object leftSucc = union(First.of(nd.getRight()), i.getAllSuccessors());  // short-circuiting happens with both truthy and falsy values
+				visit(nd.getLeft(), leftSucc, null);
+				nd.getRight().accept(this, i);
+			} else {
+				this.seq(nd.getLeft(), nd.getRight(), nd);
+				succ(nd, i.getGuardedSuccessors(nd));
+			}
 			return null;
 		}
 

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

@@ -72,6 +72,7 @@ public class ExprKinds {
 		binOpKinds.put("&=", 58);
 		binOpKinds.put("**", 87);
 		binOpKinds.put("**=", 88);
+		binOpKinds.put("??", 107);
 	}
 
 	private static final Map<String, Integer> unOpKinds = new LinkedHashMap<String, Integer>();

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

@@ -41,7 +41,7 @@ public class Main {
 	 * such a way that it may produce different tuples for the same file under the same
 	 * {@link ExtractorConfig}.
 	 */
-	public static final String EXTRACTOR_VERSION = "2018-11-22_a";
+	public static final String EXTRACTOR_VERSION = "2018-11-23";
 
 	public static final Pattern NEWLINE = Pattern.compile("\n");
 

javascript/extractor/tests/esnext/input/nullish-coalescing.js

@@ -0,0 +1,7 @@
+x1 ?? y1;
+
+x2 || y2 ?? z2;
+x3 ?? y3 || z3;
+
+x4 && y4 ?? z4;
+x5 ?? y5 && z5;

javascript/extractor/tests/esnext/output/trap/nullish-coalescing.js.trap

@@ -0,0 +1,494 @@
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+guard_node(#20131,1,#20049)
+hasLocation(#20131,#20050)
+successor(#20131,#20052)
+#20132=*
+guard_node(#20132,0,#20049)
+hasLocation(#20132,#20050)
+successor(#20132,#20055)
+successor(#20132,#20058)
+successor(#20049,#20131)
+successor(#20049,#20132)
+successor(#20052,#20055)
+successor(#20052,#20058)
+successor(#20055,#20058)
+successor(#20028,#20030)
+successor(#20030,#20032)
+successor(#20032,#20034)
+successor(#20034,#20037)
+successor(#20034,#20043)
+successor(#20034,#20040)
+#20133=*
+guard_node(#20133,1,#20037)
+hasLocation(#20133,#20038)
+successor(#20133,#20043)
+#20134=*
+guard_node(#20134,0,#20037)
+hasLocation(#20134,#20038)
+successor(#20134,#20040)
+successor(#20037,#20133)
+successor(#20037,#20134)
+successor(#20040,#20043)
+successor(#20013,#20015)
+successor(#20015,#20017)
+successor(#20017,#20019)
+#20135=*
+guard_node(#20135,1,#20019)
+hasLocation(#20135,#20020)
+successor(#20135,#20025)
+successor(#20135,#20028)
+#20136=*
+guard_node(#20136,0,#20019)
+hasLocation(#20136,#20020)
+successor(#20136,#20022)
+successor(#20019,#20135)
+successor(#20019,#20136)
+successor(#20022,#20025)
+successor(#20022,#20028)
+successor(#20025,#20028)
+successor(#20003,#20005)
+successor(#20005,#20007)
+successor(#20007,#20010)
+successor(#20007,#20013)
+successor(#20010,#20013)
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+numlines(#10000,7,5,0)
+filetype(#10000,"javascript")

javascript/ql/src/semmle/javascript/Expr.qll

@@ -1288,6 +1288,15 @@ class LogOrExpr extends @logorexpr, BinaryExpr {
   override ControlFlowNode getFirstControlFlowNode() { result = this }
 }
 
+/** A nullish coalescing '??' expression. */
+class NullishCoalescingExpr extends @nullishcoalescingexpr, BinaryExpr {
+  override string getOperator() {
+    result = "??"
+  }
+
+  override ControlFlowNode getFirstControlFlowNode() { result = this }
+}
+
 /**
  * A logical binary expression, that is, either a logical
  * 'or' or a logical 'and' expression.
@@ -1295,7 +1304,8 @@ class LogOrExpr extends @logorexpr, BinaryExpr {
 class LogicalBinaryExpr extends BinaryExpr {
   LogicalBinaryExpr() {
     this instanceof LogAndExpr or
-    this instanceof LogOrExpr
+    this instanceof LogOrExpr or
+    this instanceof NullishCoalescingExpr
   }
 }
 

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -338,6 +338,7 @@ case @expr.kind of
 | 104 = @decorator_list
 | 105 = @non_null_assertion
 | 106 = @bigintliteral
+| 107 = @nullishcoalescingexpr
 ;
 
 @varaccess = @proper_varaccess | @export_varaccess;
@@ -357,7 +358,7 @@ case @expr.kind of
 
 @comparison = @equalitytest | @ltexpr | @leexpr | @gtexpr | @geexpr;
 
-@binaryexpr = @comparison | @lshiftexpr | @rshiftexpr | @urshiftexpr | @addexpr | @subexpr | @mulexpr | @divexpr | @modexpr | @expexpr | @bitorexpr | @xorexpr | @bitandexpr | @inexpr | @instanceofexpr | @logandexpr | @logorexpr;
+@binaryexpr = @comparison | @lshiftexpr | @rshiftexpr | @urshiftexpr | @addexpr | @subexpr | @mulexpr | @divexpr | @modexpr | @expexpr | @bitorexpr | @xorexpr | @bitandexpr | @inexpr | @instanceofexpr | @logandexpr | @logorexpr | @nullishcoalescingexpr;
 
 @assignment = @assignexpr | @assignaddexpr | @assignsubexpr | @assignmulexpr | @assigndivexpr | @assignmodexpr | @assignexpexpr | @assignlshiftexpr | @assignrshiftexpr | @assignurshiftexpr | @assignorexpr | @assignxorexpr | @assignandexpr;
 
@@ -1081,4 +1082,4 @@ xmllocations(
 
 isOptionalChaining(int id: @optionalchainable ref);
 
-/* Last updated 2018/10/22. */
+/* Last updated 2018/10/23. */

javascript/ql/src/semmlecode.javascript.dbscheme.stats

@@ -1370,6 +1370,10 @@
 <v>100</v>
 </e>
 <e>
+<k>@nullishcoalescingexpr</k>
+<v>100</v>
+</e>
+<e>
 <k>@xmldtd</k>
 <v>1</v>
 </e>
@@ -1397,6 +1401,10 @@
 <k>@optionalchainable</k>
 <v>100</v>
 </e>
+<e>
+<k>@nullishcoalescingexpr</k>
+<v>100</v>
+</e>
 </typesizes>
 <stats>
 <relation>

javascript/ql/test/library-tests/DataFlow/flowStep.expected

@@ -25,6 +25,7 @@
 | tst.js:4:5:4:12 | y | tst.js:12:6:12:6 | y |
 | tst.js:4:5:4:12 | y | tst.js:13:5:13:5 | y |
 | tst.js:4:5:4:12 | y | tst.js:14:9:14:9 | y |
+| tst.js:4:5:4:12 | y | tst.js:105:6:105:6 | y |
 | tst.js:4:9:4:12 | "hi" | tst.js:4:5:4:12 | y |
 | tst.js:9:2:9:2 | x | tst.js:9:1:9:3 | (x) |
 | tst.js:10:4:10:4 | y | tst.js:10:1:10:4 | x, y |
@@ -59,6 +60,7 @@
 | tst.js:25:1:25:3 | x | tst.js:32:1:32:0 | x |
 | tst.js:25:1:25:3 | x | tst.js:57:7:57:7 | x |
 | tst.js:25:1:25:3 | x | tst.js:58:11:58:11 | x |
+| tst.js:25:1:25:3 | x | tst.js:105:1:105:1 | x |
 | tst.js:28:2:28:1 | x | tst.js:29:3:29:3 | x |
 | tst.js:28:2:29:3 | () =>\\n  x | tst.js:28:1:30:1 | (() =>\\n ... ables\\n) |
 | tst.js:29:3:29:3 | x | tst.js:28:1:30:3 | (() =>\\n ... les\\n)() |
@@ -117,6 +119,8 @@
 | tst.js:101:13:101:16 | rest | tst.js:101:3:101:16 | [ , z ] = rest |
 | tst.js:102:10:102:18 | x + y + z | tst.js:98:1:103:17 | (functi ... 3, 0 ]) |
 | tst.js:103:4:103:16 | [ 19, 23, 0 ] | tst.js:98:11:98:24 | [ x, ...rest ] |
+| tst.js:105:1:105:1 | x | tst.js:105:1:105:6 | x ?? y |
+| tst.js:105:6:105:6 | y | tst.js:105:1:105:6 | x ?? y |
 | tst.ts:1:1:1:1 | A | tst.ts:1:11:1:11 | A |
 | tst.ts:1:1:1:1 | A | tst.ts:7:1:7:0 | A |
 | tst.ts:1:1:5:1 | A | tst.ts:7:1:7:0 | A |

javascript/ql/test/library-tests/DataFlow/tst.js

@@ -102,4 +102,5 @@ var vs2 = ( for (v of o) v );     // generator comprehensions are not analysed
   return x + y + z;
 })([ 19, 23, 0 ]);
 
+x ?? y;                           // flow through short-circuiting operator
 // semmle-extractor-options: --experimental

javascript/ql/test/library-tests/TypeInference/NullishCoalescing/test.expected

@@ -0,0 +1,19 @@
+| v1 | file://:0:0:0:0 | true |
+| v2 | file://:0:0:0:0 | false |
+| v2 | file://:0:0:0:0 | undefined |
+| v4 | file://:0:0:0:0 | false |
+| v4 | file://:0:0:0:0 | true |
+| v4 | file://:0:0:0:0 | undefined |
+| v5 | file://:0:0:0:0 | false |
+| v5 | file://:0:0:0:0 | true |
+| v5 | file://:0:0:0:0 | undefined |
+| v6 | file://:0:0:0:0 | false |
+| v6 | file://:0:0:0:0 | true |
+| v6 | file://:0:0:0:0 | undefined |
+| v7 | file://:0:0:0:0 | false |
+| v7 | file://:0:0:0:0 | true |
+| v7 | file://:0:0:0:0 | undefined |
+| v7 | tst.js:22:15:22:16 | object literal |
+| x | file://:0:0:0:0 | false |
+| x | file://:0:0:0:0 | true |
+| x | file://:0:0:0:0 | undefined |

javascript/ql/test/library-tests/TypeInference/NullishCoalescing/test.ql

@@ -0,0 +1,5 @@
+import javascript
+
+from Variable v, Expr e
+where e = v.getAnAssignedExpr()
+select v, e.analyze().getAValue()

javascript/ql/test/library-tests/TypeInference/NullishCoalescing/tst.js

@@ -0,0 +1,24 @@
+(function() {
+    var x = f()? undefined: f()? false: true;
+
+    if (x || false) {
+        v1 = x;
+    } else {
+        v2 = x;
+    }
+
+    if (x && false) {
+        v3 = x;
+    } else {
+        v4 = x;
+    }
+
+    if (x ?? false) {
+        v5 = x;
+    } else {
+        v6 = x;
+    }
+
+    v7 = x ?? {};
+});
+// semmle-extractor-options: --experimental

javascript/upgrades/81e6619c681f7844e8ddc38db102e75b428c830c/upgrade.properties

@@ -0,0 +1,2 @@
+description: 'introduce @nullishcoalescingexpr'
+compatibility: backwards