TS: Support type-only import/export

javascript/ql/src/semmle/javascript/AST.qll

@@ -125,7 +125,7 @@ class ASTNode extends @ast_node, Locatable {
    * Holds if this is part of an ambient declaration or type annotation in a TypeScript file.
    *
    * A declaration is ambient if it occurs under a `declare` modifier or is
-   * an interface declaration, type alias, or type annotation.
+   * an interface declaration, type alias, type annotation, or type-only import/export declaration.
    *
    * The TypeScript compiler emits no code for ambient declarations, but they
    * can affect name resolution and type checking at compile-time.

javascript/ql/src/semmle/javascript/ES2015Modules.qll

@@ -76,6 +76,16 @@ class ImportDeclaration extends Stmt, Import, @importdeclaration {
     // `import { createServer } from 'http'`
     result = DataFlow::destructuredModuleImportNode(this)
   }
+
+  /** Holds if this is declared with the `type` keyword, so it only imports types. */
+  predicate isTypeOnly() {
+    hasTypeKeyword(this)
+  }
+
+  override predicate isAmbient() {
+    Stmt.super.isAmbient() or
+    isTypeOnly()
+  }
 }
 
 /** A literal path expression appearing in an `import` declaration. */
@@ -256,6 +266,16 @@ abstract class ExportDeclaration extends Stmt, @exportdeclaration {
    * to module `a` or possibly to some other module from which `a` re-exports.
    */
   abstract DataFlow::Node getSourceNode(string name);
+
+  /** Holds if is declared with the `type` keyword, so only types are exported. */
+  predicate isTypeOnly() {
+    hasTypeKeyword(this)
+  }
+
+  override predicate isAmbient() {
+    Stmt.super.isAmbient() or
+    isTypeOnly()
+  }
 }
 
 /**
@@ -413,6 +433,18 @@ class ExportNamedDeclaration extends ExportDeclaration, @exportnameddeclaration
   }
 }
 
+/**
+ * An export declaration with the `type` modifier.
+ */
+private class TypeOnlyExportDeclaration extends ExportNamedDeclaration {
+  TypeOnlyExportDeclaration() { isTypeOnly() }
+
+  override predicate exportsAs(LexicalName v, string name) {
+    super.exportsAs(v, name) and
+    not v instanceof Variable
+  }
+}
+
 /**
  * An export specifier in an export declaration.
  *

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -385,6 +385,8 @@ case @expr.kind of
 
 @exportspecifier = @namedexportspecifier | @exportdefaultspecifier | @exportnamespacespecifier;
 
+@import_or_export_declaration = @importdeclaration | @exportdeclaration;
+
 @typeassertion = @astypeassertion | @prefixtypeassertion;
 
 @classdefinition = @classdeclstmt | @classexpr;
@@ -518,6 +520,7 @@ hasPublicKeyword (int id: @property ref);
 hasPrivateKeyword (int id: @property ref);
 hasProtectedKeyword (int id: @property ref);
 hasReadonlyKeyword (int id: @property ref);
+hasTypeKeyword (int id: @import_or_export_declaration ref);
 isOptionalMember (int id: @property ref);
 hasDefiniteAssignmentAssertion (int id: @field_or_vardeclarator ref);
 isOptionalParameterDeclaration (unique int parameter: @pattern ref);