From 7b2ec05b2ec247de83901e8504f7ba711d6027bb Mon Sep 17 00:00:00 2001
From: Ben Chaimberg <chaimber@amazon.com>
Date: Wed, 21 Jul 2021 09:01:26 -0700
Subject: [PATCH] feat(rosetta): hoist declare statements to top-level of
 document (#2897)

`declare` statements allow snippet writers to create a mock variable of a certain type that can be used within a snippet without having to provide a concrete value of that type. This is useful when referencing a type from another module without needing to create an instance of that type, which may be complex. Example:
```
declare const lambdaFunction: lambda.Function;
const myResource = ...
myResource.grantRead(lambdaFunction);
```
`declare` statements can only exist at the top level of a document, meaning snippets with fixtures may not be able to define a `declare` statement, since the snippet may be embedded into the fixture within a class, function, etc. This feature "hoists" `declare` statements to the top level of the document, similarly to how `import` statements are hoisted currently.
---
 packages/jsii-rosetta/lib/fixtures.ts         | 17 +++++-----
 packages/jsii-rosetta/test/fixtures.test.ts   | 31 +++++++++++++++++++
 .../test/rosetta/default.ts-fixture           |  1 +
 3 files changed, 42 insertions(+), 7 deletions(-)
 create mode 100644 packages/jsii-rosetta/test/rosetta/default.ts-fixture

diff --git a/packages/jsii-rosetta/lib/fixtures.ts b/packages/jsii-rosetta/lib/fixtures.ts
index 91276ca1ed..e87272c2ad 100644
--- a/packages/jsii-rosetta/lib/fixtures.ts
+++ b/packages/jsii-rosetta/lib/fixtures.ts
@@ -147,13 +147,16 @@ function sidelineImports(source: string): {
     ScriptKind.TS,
   );
   for (const statement of sourceFile.statements) {
-    switch (statement.kind) {
-      case SyntaxKind.ImportDeclaration:
-      case SyntaxKind.ImportEqualsDeclaration:
-        imports += statement.getFullText(sourceFile);
-        break;
-      default:
-        statements += statement.getFullText(sourceFile);
+    if (
+      statement.kind === SyntaxKind.ImportDeclaration ||
+      statement.kind === SyntaxKind.ImportEqualsDeclaration ||
+      (statement.kind === SyntaxKind.VariableStatement &&
+        statement.getChildAt(0).getChildAt(0).kind ===
+          SyntaxKind.DeclareKeyword)
+    ) {
+      imports += statement.getFullText(sourceFile);
+    } else {
+      statements += statement.getFullText(sourceFile);
     }
   }
 
diff --git a/packages/jsii-rosetta/test/fixtures.test.ts b/packages/jsii-rosetta/test/fixtures.test.ts
index 92e9f9ff7c..d315e86b17 100644
--- a/packages/jsii-rosetta/test/fixtures.test.ts
+++ b/packages/jsii-rosetta/test/fixtures.test.ts
@@ -16,4 +16,35 @@ describe('fixturize', () => {
 
     expect(fixturize(snippet)).toEqual(expect.objectContaining(snippet));
   });
+
+  test('separates imports and declarations', () => {
+    const source = `import * as ns from 'mod';
+declare const mock: Tpe;
+const val = new Cls();`;
+    const snippet = {
+      visibleSource: source,
+      where: 'where',
+      parameters: {
+        [SnippetParameters.$PROJECT_DIRECTORY]: 'test',
+      },
+      strict: true,
+    };
+
+    const fixturizedSnippet = fixturize(snippet);
+
+    expect(fixturizedSnippet.completeSource)
+      .toBe(`// Hoisted imports begin after !show marker below
+/// !show
+import * as ns from 'mod';
+declare const mock: Tpe;
+/// !hide
+// Hoisted imports ended before !hide marker above
+// Code snippet begins after !show marker below
+/// !show
+
+const val = new Cls();
+/// !hide
+// Code snippet ended before !hide marker above
+`);
+  });
 });
diff --git a/packages/jsii-rosetta/test/rosetta/default.ts-fixture b/packages/jsii-rosetta/test/rosetta/default.ts-fixture
new file mode 100644
index 0000000000..acd85cb41b
--- /dev/null
+++ b/packages/jsii-rosetta/test/rosetta/default.ts-fixture
@@ -0,0 +1 @@
+/// here