JS: Follow immediate predecessors in path resolution

Author: asgerf

javascript/ql/lib/semmle/javascript/Paths.qll

@@ -380,6 +380,25 @@ private class PathExprString extends PathString {
   }
 }
 
+pragma[nomagic]
+private DataFlow::Node getAPathExprAlias(PathExpr expr) {
+  result.getImmediatePredecessor().asExpr() = expr
+  or
+  result.getImmediatePredecessor() = getAPathExprAlias(expr)
+}
+
+private class PathExprFromAlias extends PathExpr {
+  private PathExpr other;
+
+  PathExprFromAlias() { this = getAPathExprAlias(other).asExpr() }
+
+  override string getValue() { result = other.getValue() }
+
+  override Folder getAdditionalSearchRoot(int priority) {
+    result = other.getAdditionalSearchRoot(priority)
+  }
+}
+
 /**
  * A path expression of the form `p + q`, where both `p` and `q`
  * are path expressions.
@@ -413,6 +432,9 @@ private class ConcatPath extends PathExpr {
  * Examples include arguments to the CommonJS `require` function or AMD dependency arguments.
  */
 abstract class PathExprCandidate extends Expr {
+  pragma[nomagic]
+  private Expr getAPart1() { result = this or result = this.getAPart().getAChildExpr() }
+
   /**
    * Gets an expression that is nested inside this expression.
    *
@@ -421,5 +443,5 @@ abstract class PathExprCandidate extends Expr {
    * `ConstantString`s).
    */
   pragma[nomagic]
-  Expr getAPart() { result = this or result = this.getAPart().getAChildExpr() }
+  Expr getAPart() { result = this.getAPart1().flow().getImmediatePredecessor*().asExpr() }
 }

javascript/ql/test/library-tests/Modules/import-indirect-path.js

@@ -0,0 +1,5 @@
+require(__dirname + '/a');
+
+var x = __dirname;
+var y = '/a';
+require(x + y);

javascript/ql/test/library-tests/Modules/tests.expected

@@ -90,6 +90,8 @@ test_NamedImportSpecifier
 | reExportNamespaceClient.js:1:10:1:11 | ns |
 test_OtherImports
 | es2015_require.js:1:11:1:24 | require('./d') | d.js:1:1:5:0 | <toplevel> |
+| import-indirect-path.js:1:1:1:25 | require ... + '/a') | a.js:1:1:5:32 | <toplevel> |
+| import-indirect-path.js:5:1:5:14 | require(x + y) | a.js:1:1:5:32 | <toplevel> |
 test_ReExportDeclarations
 | b.js:7:1:7:21 | export  ...  './a'; | b.js:7:16:7:20 | './a' |
 | d.js:4:1:4:20 | export * from 'm/c'; | d.js:4:15:4:19 | 'm/c' |
@@ -103,6 +105,7 @@ test_getAnImportedModule
 | library-tests/Modules/es2015_require.js | library-tests/Modules/d.js |
 | library-tests/Modules/f.ts | library-tests/Modules/e.js |
 | library-tests/Modules/g.ts | library-tests/Modules/f.ts |
+| library-tests/Modules/import-indirect-path.js | library-tests/Modules/a.js |
 | library-tests/Modules/import-ts-with-js-extension.ts | library-tests/Modules/f.ts |
 | library-tests/Modules/m/c.js | library-tests/Modules/b.js |
 | library-tests/Modules/reExportNamespaceClient.js | library-tests/Modules/reExportNamespace.js |