dist/ruby/nodes/patterns.js in prettier-2.0.0.pre.rc4 vs dist/ruby/nodes/patterns.js in prettier-2.0.0

@@ -17,28 +17,40 @@
     }
     return path.call(print);
 };
 const printAryPtn = (path, opts, print) => {
     const [constant, preargs, splatarg, postargs] = path.getValue().body;
-    let args = [];
+    let argDocs = [];
     if (preargs) {
-        args = args.concat(path.map((argPath) => printPatternArg(argPath, opts, print), "body", 1));
+        argDocs = argDocs.concat(path.map((argPath) => printPatternArg(argPath, opts, print), "body", 1));
     }
     if (splatarg) {
-        args.push(["*", path.call(print, "body", 2)]);
+        argDocs.push(["*", path.call(print, "body", 2)]);
     }
     if (postargs) {
-        args = args.concat(path.map(print, "body", 3));
+        argDocs = argDocs.concat(path.map(print, "body", 3));
     }
-    args = group(join([",", line], args));
-    if (constant || patterns.includes(path.getParentNode().type)) {
-        args = ["[", args, "]"];
+    let argDoc = group(join([",", line], argDocs));
+    // There are a couple of cases where we _must_ use brackets. They include:
+    //
+    // * When the number of arguments inside the array pattern is one 1, then we
+    //   have to include them, otherwise it matches the whole array. Consider the
+    //   difference between `in [elem]` and `in elem`.
+    // * If we have a wrapping constant, then we definitely need the brackets.
+    //   Consider the difference between `in Const[elem]` and `in Const elem`
+    // * If we're nested inside a parent pattern, then we have to have brackets.
+    //   Consider the difference between `in key: first, second` and
+    //   `in key: [first, second]`.
+    if (argDocs.length === 1 ||
+        constant ||
+        patterns.includes(path.getParentNode().type)) {
+        argDoc = ["[", argDoc, "]"];
     }
     if (constant) {
-        return [path.call(print, "body", 0), args];
+        return [path.call(print, "body", 0), argDoc];
     }
-    return args;
+    return argDoc;
 };
 exports.printAryPtn = printAryPtn;
 const printFndPtn = (path, opts, print) => {
     const [constant] = path.getValue().body;
     const docs = [
@@ -84,12 +96,13 @@
     }
     return args;
 };
 exports.printHshPtn = printHshPtn;
 const printIn = (path, opts, print) => {
+    const keyword = "in ";
     const parts = [
-        "in ",
-        align("in ".length, path.call((valuePath) => printPatternArg(valuePath, opts, print), "body", 0)),
+        keyword,
+        align(keyword.length, path.call((valuePath) => printPatternArg(valuePath, opts, print), "body", 0)),
         indent([hardline, path.call(print, "body", 1)])
     ];
     if (path.getValue().body[2]) {
         parts.push(hardline, path.call(print, "body", 2));
     }