fix: improve shadow_scope (#242)

Author: morgante

.grit/patterns/js/test_scope_shadow.md renamed to .grit/patterns/js/_test_scope_shadow.md

@@ -2,43 +2,16 @@
 tags: [utility, test]
 ---
 
-## Test shadow scope
-
-This tests the `shadows_identifier` pattern by finding all cases where a variable is shadowed.
+## Shadow Identifiers
 
+This tests the `scope_for_identifier` pattern by finding all cases where a variable is shadowed.
 
 ```grit
 language js
 
-// Implementation
-pattern shadows_identifier($name) {
-  or {
-    statement_block($statements) where {
-      $statements <: some variable($declarations) where {
-        $declarations <: contains variable_declarator(name=$name)
-      }
-    },
-    arrow_function($parameters) where {
-      $parameters <: contains $name
-    },
-    function_declaration($parameters) where {
-      $parameters <: contains $name
-    },
-    for_in_statement() as $statement where {
-      $statement <: contains $name
-    },
-    for_statement() as $statement where {
-      $statement <: contains $name
-    },
-    `try { $_ } catch($catch) { $_ }` where {
-      $catch <: contains $name
-    },
-  }
-}
-
 // Test case
 file($body) where {
-  $body <: contains bubble shadows_identifier(`x`) as $scope where {
+  $body <: contains bubble identifier_scope(`x`) as $scope where {
     $scope <: contains `x` => `shadowed`
   }
 }
@@ -68,6 +41,28 @@ function notShadowingVar() {
 shadowingExample();
 ```
 
+## Anonymous function variable definition
+
+```js
+var shadowingExample = function (x) {
+  console.log(x);
+};
+var notShadowingVar = function (y) {
+  console.log(y);
+};
+shadowingExample();
+```
+
+```js
+var shadowingExample = function (shadowed) {
+  console.log(shadowed);
+};
+var notShadowingVar = function (y) {
+  console.log(y);
+};
+shadowingExample();
+```
+
 ## If statement
 
 ```js

.grit/patterns/js/replace_wildcard_imports.md

@@ -30,7 +30,7 @@ pattern replace_wildcard_import() {
   `import * as $alias from $src` as $import where {
     $refs = [],
     $kept_refs = [],
-    $program <: contains used_alias($alias, $refs, $kept_refs) until shadows_identifier(name=$alias),
+    $program <: contains used_alias($alias, $refs, $kept_refs) until identifier_scope(name=$alias),
     $refs = distinct($refs),
     $joined_refs = join($refs, `, `),
     // Try the different scenarios

.grit/patterns/js/shadow_scope.grit

@@ -0,0 +1,28 @@
+
+pattern identifier_scope($name) {
+  or {
+    statement_block($statements) where {
+      $statements <: some variable($declarations) where {
+        $declarations <: contains variable_declarator(name=$name)
+      }
+    },
+    function($parameters) where {
+      $parameters <: contains $name
+    },
+    arrow_function($parameters) where {
+      $parameters <: contains $name
+    },
+    function_declaration($parameters) where {
+      $parameters <: contains $name
+    },
+    for_in_statement() as $statement where {
+      $statement <: contains $name
+    },
+    for_statement() as $statement where {
+      $statement <: contains $name
+    },
+    `try { $_ } catch($catch) { $_ }` where {
+      $catch <: contains $name
+    },
+  }
+}

.grit/patterns/js/variable_scoping.md

@@ -0,0 +1,56 @@
+---
+tags:
+  - docs
+  - full-examples
+---
+
+# Variable Scoping with `identifier_scope`
+
+Default Grit patterns are not generally aware of variable scoping, but you can use the `identifier_scope` pattern to find (or exclude) [scopes](https://developer.mozilla.org/en-US/docs/Glossary/Scope) where an identifier has been _locally_ defined.
+
+This is most often used when you want to target an import from a shared module but exclude scopes where the identifier is shadowed locally.
+
+For example, this pattern would rename `t` from the `translation` library to `translate` unless `t` is shadowed locally:
+
+```grit
+language js
+
+`t` as $t => `translate` where {
+  $t <: imported_from(from=`"translation"`),
+  $t <: not within identifier_scope(name=`t`)
+}
+```
+
+Here is a simple example file where `t` is shadowed locally:
+
+```js
+import { t } from 'translation';
+
+console.log(t('hello world'));
+
+function normal() {
+  console.log(t('hello world'));
+}
+
+// t is an argument to this function, so the global t is not used and we should *not* rename it here.
+function shadowed(t) {
+  console.log(t('hello world'));
+}
+```
+
+When we rewrite it, the shadowed `t` is not renamed:
+
+```js
+import { translate } from 'translation';
+
+console.log(translate('hello world'));
+
+function normal() {
+  console.log(translate('hello world'));
+}
+
+// t is an argument to this function, so the global t is not used and we should *not* rename it here.
+function shadowed(t) {
+  console.log(t('hello world'));
+}
+```