Fix using concat() on single Doc (#9994)

Co-authored-by: Sosuke Suzuki <aosukeke@gmail.com>

.eslintrc.yml

@@ -111,6 +111,7 @@ overrides:
   - files: src/**/*.js
     rules:
       prettier-internal-rules/no-doc-builder-concat: off
+      prettier-internal-rules/no-single-doc-concat: error
       prettier-internal-rules/prefer-fast-path-each: error
       prettier-internal-rules/prefer-is-non-empty-array: error
   - files: src/document/*.js

scripts/tools/eslint-plugin-prettier-internal-rules/index.js

@@ -7,6 +7,7 @@ module.exports = {
     "jsx-identifier-case": require("./jsx-identifier-case"),
     "no-doc-builder-concat": require("./no-doc-builder-concat"),
     "no-node-comments": require("./no-node-comments"),
+    "no-single-doc-concat": require("./no-single-doc-concat"),
     "prefer-fast-path-each": require("./prefer-fast-path-each"),
     "prefer-is-non-empty-array": require("./prefer-is-non-empty-array"),
     "require-json-extensions": require("./require-json-extensions"),

scripts/tools/eslint-plugin-prettier-internal-rules/no-single-doc-concat.js

@@ -0,0 +1,44 @@
+"use strict";
+
+// TODO: Remove this rule when deprecated `concat` is not using in codebase, #9993.
+
+const selector = [
+  "CallExpression",
+  '[callee.type="Identifier"]',
+  '[callee.name="concat"]',
+  "[arguments.length=1]",
+  '[arguments.0.type="ArrayExpression"]',
+  "[arguments.0.elements.length=1]",
+].join("");
+
+const messageId = "no-single-doc-concat";
+
+module.exports = {
+  meta: {
+    type: "suggestion",
+    docs: {
+      url:
+        "https://github.com/prettier/prettier/blob/master/scripts/eslint-plugin-prettier-internal-rules/no-single-doc-concat.js",
+    },
+    messages: {
+      [messageId]: "Do not use `concat()` to concat single `Doc`.",
+    },
+    fixable: "code",
+  },
+  create(context) {
+    const sourceCode = context.getSourceCode();
+    return {
+      [selector](node) {
+        context.report({
+          node,
+          messageId,
+          fix: (fixer) =>
+            fixer.replaceText(
+              node,
+              sourceCode.getText(node.arguments[0].elements[0])
+            ),
+        });
+      },
+    };
+  },
+};

scripts/tools/eslint-plugin-prettier-internal-rules/test.js

@@ -144,6 +144,17 @@ test("no-node-comments", {
   ],
 });
 
+test("no-single-doc-concat", {
+  valid: [],
+  invalid: [
+    {
+      code: 'concat([path.call(print, "params")])',
+      output: 'path.call(print, "params")',
+      errors: 1,
+    },
+  ],
+});
+
 test("prefer-fast-path-each", {
   valid: ["const foo = path.map()"],
   invalid: [

src/language-css/printer-postcss.js

@@ -213,7 +213,7 @@ function genericPrint(path, options, print) {
         if (node.function) {
           return concat([
             node.name,
-            concat([path.call(print, "params")]),
+            path.call(print, "params"),
             isTemplatePlaceholderNodeWithoutSemiColon ? "" : ";",
           ]);
         }
@@ -223,7 +223,7 @@ function genericPrint(path, options, print) {
             "@",
             node.name,
             ": ",
-            node.value ? concat([path.call(print, "value")]) : "",
+            node.value ? path.call(print, "value") : "",
             node.raws.between.trim() ? node.raws.between.trim() + " " : "",
             node.nodes
               ? concat([

src/language-graphql/printer-graphql.js

@@ -21,7 +21,7 @@ function genericPrint(path, options, print) {
     case "Document": {
       const parts = [];
       path.each((pathChild, index, definitions) => {
-        parts.push(concat([pathChild.call(print)]));
+        parts.push(pathChild.call(print));
         if (index !== definitions.length - 1) {
           parts.push(hardline);
           if (

src/language-handlebars/printer-glimmer.js

@@ -138,11 +138,14 @@ function print(path, options, print) {
       // same, there is no value for this AttrNode and it should be printed
       // without the `=""`. Example: `<img data-test>` -> `<img data-test>`
       if (isEmptyText && locStart(n.value) === locEnd(n.value)) {
-        return concat([n.name]);
+        return n.name;
       }
       const value = path.call(print, "value");
       const quotedValue = isText
-        ? printStringLiteral(getDocParts(value).join(), options)
+        ? printStringLiteral(
+            typeof value === "string" ? value : getDocParts(value).join(),
+            options
+          )
         : value;
       return concat([n.name, "=", quotedValue]);
     }
@@ -157,7 +160,7 @@ function print(path, options, print) {
     }
 
     case "Hash": {
-      return concat([join(line, path.map(print, "pairs"))]);
+      return join(line, path.map(print, "pairs"));
     }
     case "HashPair": {
       return concat([n.key, "=", path.call(print, "value")]);
@@ -201,7 +204,7 @@ function print(path, options, print) {
         // TODO: format style and srcset attributes
         // and cleanup concat that is not necessary
         if (!isInAttributeOfName(path, "class")) {
-          return concat([n.chars]);
+          return n.chars;
         }
 
         let leadingSpace = "";

src/language-js/print/call-arguments.js

@@ -82,7 +82,7 @@ function printCallArguments(path, options, print) {
 
     let shouldBreak = false;
     iterateFunctionParametersPath(argPath, (parameterPath) => {
-      shouldBreak = shouldBreak || willBreak(concat([print(parameterPath)]));
+      shouldBreak = shouldBreak || willBreak(print(parameterPath));
     });
 
     return shouldBreak;

src/language-js/print/jsx.js

@@ -118,7 +118,7 @@ function printJsxElementInternal(path, options, print) {
 
   const rawJsxWhitespace = options.singleQuote ? "{' '}" : '{" "}';
   const jsxWhitespace = isMdxBlock
-    ? concat([" "])
+    ? " "
     : ifBreak(concat([rawJsxWhitespace, softline]), " ");
 
   const isFacebookTranslationTag =

src/language-js/printer-estree.js

@@ -488,9 +488,7 @@ function printPathNoParens(path, options, print, args) {
         }, "expressions");
         return group(concat(parts));
       }
-      return group(
-        concat([join(concat([",", line]), path.map(print, "expressions"))])
-      );
+      return group(join(concat([",", line]), path.map(print, "expressions")));
     }
     case "ThisExpression":
       return "this";

src/language-yaml/print/mapping-item.js

@@ -23,7 +23,7 @@ function printMappingItem(node, parentNode, path, print, options) {
   const isEmptyMappingValue = isEmptyNode(value);
 
   if (isEmptyMappingKey && isEmptyMappingValue) {
-    return concat([": "]);
+    return ": ";
   }
 
   const printedKey = path.call(print, "key");