JS: support transform-react-jsx plugin

javascript/ql/src/Declarations/UnusedVariable.ql

@@ -56,10 +56,17 @@ predicate isPropertyFilter(UnusedLocal v) {
 predicate isReactImportForJSX(UnusedLocal v) {
   exists (ImportSpecifier is |
     is.getLocal() = v.getADeclaration() and
-    exists (JSXNode jsx | jsx.getTopLevel() = is.getTopLevel()) |
-    v.getName() = "React" or
-    // also accept legacy `@jsx` pragmas
+    exists (JSXNode jsx | jsx.getTopLevel() = is.getTopLevel())
+    |
+    v.getName() = "React"
+    or
+    // legacy `@jsx` pragmas
     exists (JSXPragma p | p.getTopLevel() = is.getTopLevel() | p.getDOMName() = v.getName())
+    or
+    // JSX pragma from a .babelrc file
+    exists (Babel::TransformReactJsxConfig plugin |
+      plugin.getConfig().getAContainerInScope() = is.getFile() and
+      plugin.getJSXFactoryVariableName() = v.getName())
   )
 }
 

javascript/ql/src/semmle/javascript/frameworks/Babel.qll

@@ -28,6 +28,18 @@ module Babel {
         result.(JSONArray).getElementStringValue(0) = pluginName
       )
     }
+
+    /**
+     * Gets a file affected by this Babel configuration.
+     */
+    Container getAContainerInScope() {
+      result = getFile().getParentContainer()
+      or
+      result = getAContainerInScope().getAChildContainer() and
+      // File-relative .babelrc search stops at any package.json or .babelrc file.
+      not result.getAChildContainer() = any(PackageJSON pkg).getFile() and
+      not result.getAChildContainer() = any(Config pkg).getFile()
+    }
   }
 
   /**
@@ -152,4 +164,33 @@ module Babel {
       result = pathExpr.getConfig().getFolder()
     }
   }
+
+  /**
+   * A configuration object for the `transform-react-jsx` plugin.
+   *
+   * The plugin option `{"pragma": xxx}` specifies a variable name used to instantiate
+   * JSX elements.
+   */
+  class TransformReactJsxConfig extends JSONArray {
+    Config cfg;
+
+    TransformReactJsxConfig() {
+      this = cfg.getPluginConfig("transform-react-jsx")
+    }
+
+    /** Gets the Babel configuration object. */
+    Config getConfig() {
+      result = cfg
+    }
+
+    /** Gets the options passed to this plugin. */
+    JSONObject getOptions() {
+      result = getElementValue(1)
+    }
+
+    /** Gets the name of the variable used to create JSX elements. */
+    string getJSXFactoryVariableName() {
+      result = getOptions().getPropStringValue("pragma")
+    }
+  }
 }

javascript/ql/test/query-tests/Declarations/UnusedVariable/UnusedVariable.expected

@@ -1,4 +1,3 @@
-| Babelrc/importPragma.jsx:1:1:1:27 | import  ... react'; | Unused import h. |
 | Babelrc/importPragma.jsx:2:1:2:27 | import  ... react'; | Unused import q. |
 | decorated.ts:1:1:1:126 | import  ... where'; | Unused import actionHandler. |
 | decorated.ts:4:10:4:12 | fun | Unused function fun. |