fix: add EOL at the end of a JSON file

lib/file.ts

@@ -1,7 +1,7 @@
-import { detectEOL } from "./std/fs.ts";
+import { detectEOL, EOL, formatEOL } from "./std/fs.ts";
 import { toUrl } from "./dependency.ts";
 import { type DependencyUpdate } from "./update.ts";
-import { readImportMapJson } from "./import_map.ts";
+import { parseImportMapJson } from "./import_map.ts";
 
 /**
  * Write the given array of DependencyUpdate to files.
@@ -102,7 +102,7 @@ async function writeToModule(
     ) => [dependency.code.span.start.line, dependency]),
   );
   const content = await Deno.readTextFile(update.path);
-  const eol = detectEOL(content) ?? "\n";
+  const eol = detectEOL(content) ?? EOL;
   await Deno.writeTextFile(
     update.path,
     content
@@ -127,9 +127,14 @@ async function writeToImportMap(
   /** The dependency update to apply. */
   update: FileUpdate<"import_map">,
 ) {
-  const json = await readImportMapJson(update.path);
+  const content = await Deno.readTextFile(update.path);
+  const json = parseImportMapJson(content);
   for (const dependency of update.dependencies) {
     json.imports[dependency.map.key] = toUrl(dependency.to);
   }
-  await Deno.writeTextFile(update.path, JSON.stringify(json, null, 2));
+  const eol = detectEOL(content) ?? EOL;
+  await Deno.writeTextFile(
+    update.path,
+    formatEOL(JSON.stringify(json, null, 2), eol) + eol,
+  );
 }

lib/import_map.ts

@@ -53,12 +53,21 @@ export async function readImportMapJson(
 ): Promise<ImportMapJson> {
   const data = await Deno.readTextFile(url);
   try {
-    return ensure(parseJsonc(data), isImportMapJson);
+    return parseImportMapJson(data);
   } catch {
     throw new SyntaxError(`${url} does not have a valid import map`);
   }
 }
 
+/**
+ * Parse a JSON including import maps from the given string.
+ */
+export function parseImportMapJson(
+  data: string,
+): ImportMapJson {
+  return ensure(parseJsonc(data), isImportMapJson);
+}
+
 /**
  * Read an import map from the given file path or URL.
  * @param url - The URL of the import map.

lib/std/fs.ts

@@ -1,6 +1,7 @@
 export { existsSync } from "https://deno.land/std@0.218.2/fs/exists.ts";
 export {
   detect as detectEOL,
+  EOL,
   format as formatEOL,
   LF,
 } from "https://deno.land/std@0.218.2/fs/eol.ts";

test/snapshots/file_test.ts.snap

@@ -224,7 +224,8 @@ snapshot[`write - import_map_referred/mod.ts 1`] = `
   "imports": {
     "dax": "https://deno.land/x/dax@123.456.789/mod.ts"
   }
-}',
+}
+',
 ]
 `;
 
@@ -418,7 +419,8 @@ snapshot[`write - import_map/mod.ts 1`] = `
     "flag": "jsr:@luca/flag@123.456.789",
     "/": "./"
   }
-}',
+}
+',
 ]
 `;