Add POC

.gitignore

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+node_modules/

4.7.4.d.ts

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+declare module "main" {
+    export const main: ({ conflict: a }: {
+        conflict: number;
+    }, { conflict: b }: {
+        conflict: number;
+    }, { dupe: c, dupe: d }: {
+        dupe: number;
+    }, { function: e }: {
+        function: number;
+    }) => number;
+}

4.7.4/package.json

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+{
+  "devDependencies": {
+    "typescript": "4.7.4"
+  },
+  "scripts": {
+    "build": "tsc --declaration --emitDeclarationOnly --outfile ../4.7.4.d.ts ../main.ts"
+  }
+}

4.8.3.d.ts

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+declare module "main" {
+    export const main: ({ conflict }: {
+        conflict: number;
+    }, { conflict }: {
+        conflict: number;
+    }, { dupe, dupe }: {
+        dupe: number;
+    }, { function }: {
+        function: number;
+    }) => number;
+}

4.8.3/package.json

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+{
+  "devDependencies": {
+    "typescript": "4.8.3"
+  },
+  "scripts": {
+    "build": "tsc --declaration --emitDeclarationOnly --outfile ../4.8.3.d.ts ../main.ts"
+  }
+}

README.md

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 # TypeScript 4.8 declaration poc
+
+```shell
+npm install
+```
+
+```shell
+npm run build
+
+# > build
+# > npm run --quiet build --workspaces
+#
+#
+# > build
+# > tsc --declaration --emitDeclarationOnly --outfile ../4.7.4.d.ts ../main.ts
+#
+# > build
+# > tsc --declaration --emitDeclarationOnly --outfile ../4.8.3.d.ts ../main.ts
+```
+
+```shell
+npm run lint
+
+# > lint
+# > tsc --noEmit *.d.ts
+#
+# 4.8.3.d.ts:8:19 - error TS1005: ':' expected.
+#
+# 8     }, { function }: {
+#                     ~
+#
+#
+# Found 1 error in 4.8.3.d.ts:8
+```

main.ts

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+export const main = (
+  { conflict: a }: { conflict: number },
+  { conflict: b }: { conflict: number },
+  { dupe: c, dupe: d }: { dupe: number },
+  { function: e }: { function: number }
+) => a + b + c + d + e;

package.json

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+{
+  "scripts": {
+    "build": "npm run build --workspaces",
+    "lint": "tsc --noEmit *.d.ts"
+  },
+  "workspaces": [
+    "4.7.4",
+    "4.8.3"
+  ]
+}