allow linebreaks in member expressions in template interpolations (#16116)

* allow linebreaks in member expressions in template interpolations

* lint

* add changelog

changelog_unreleased/javascript/16116.md

@@ -0,0 +1,19 @@
+#### Allow linebreaks in member expressions in template interpolations (#16116 by @bakkot)
+
+When there is already a linebreak in a template interpolation, allow it to stay there even if it is a member expression. Note that (as of [#15209](https://github.com/prettier/prettier/pull/15209)) Prettier will not insert a linebreak inside an interpolation when one is not already present.
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+`template with ${
+    very.very.very.very.very.very.very.very.very.very.very.long.chain
+}`;
+
+// Prettier stable
+`template with ${very.very.very.very.very.very.very.very.very.very.very.long.chain}`;
+
+// Prettier main
+`template with ${
+  very.very.very.very.very.very.very.very.very.very.very.long.chain
+}`;
+```

src/language-js/print/template-literal.js

@@ -20,7 +20,6 @@ import {
   isBinaryCastExpression,
   isBinaryish,
   isMemberExpression,
-  isSimpleTemplateLiteral,
 } from "../utils/index.js";
 
 function printTemplateLiteral(path, print, options) {
@@ -39,18 +38,7 @@ function printTemplateLiteral(path, print, options) {
   }
   const parts = [];
 
-  let expressionDocs = path.map(print, expressionsKey);
-  const isSimple = isSimpleTemplateLiteral(node);
-
-  if (isSimple) {
-    expressionDocs = expressionDocs.map(
-      (doc) =>
-        printDocToString(doc, {
-          ...options,
-          printWidth: Number.POSITIVE_INFINITY,
-        }).formatted,
-    );
-  }
+  const expressionDocs = path.map(print, expressionsKey);
 
   parts.push(lineSuffixBoundary, "`");
 
@@ -82,44 +70,43 @@ function printTemplateLiteral(path, print, options) {
 
     let expressionDoc = expressionDocs[index];
 
-    if (!isSimple) {
-      const expression = node[expressionsKey][index];
+    const expression = node[expressionsKey][index];
 
-      let interpolationHasNewline = hasNewlineInRange(
-        options.originalText,
-        locEnd(quasi),
-        locStart(node.quasis[index + 1]),
-      );
+    let interpolationHasNewline = hasNewlineInRange(
+      options.originalText,
+      locEnd(quasi),
+      locStart(node.quasis[index + 1]),
+    );
 
-      if (!interpolationHasNewline) {
-        // Never add a newline to an interpolation which didn't already have one...
-        const renderedExpression = printDocToString(expressionDoc, {
-          ...options,
-          printWidth: Number.POSITIVE_INFINITY,
-        }).formatted;
+    if (!interpolationHasNewline) {
+      // Never add a newline to an interpolation which didn't already have one...
+      const renderedExpression = printDocToString(expressionDoc, {
+        ...options,
+        printWidth: Number.POSITIVE_INFINITY,
+      }).formatted;
 
-        // ... unless one will be introduced anyway, e.g. by a nested function.
-        // This case is rare, so we can pay the cost of re-rendering.
-        if (renderedExpression.includes("\n")) {
-          interpolationHasNewline = true;
-        } else {
-          expressionDoc = renderedExpression;
-        }
+      // ... unless one will be introduced anyway, e.g. by a nested function.
+      // This case is rare, so we can pay the cost of re-rendering.
+      if (renderedExpression.includes("\n")) {
+        interpolationHasNewline = true;
+      } else {
+        expressionDoc = renderedExpression;
       }
+    }
 
-      // Breaks at the template element boundaries (${ and }) are preferred to breaking
-      // in the middle of a MemberExpression
-      if (
-        interpolationHasNewline &&
-        (hasComment(expression) ||
-          isMemberExpression(expression) ||
-          expression.type === "ConditionalExpression" ||
-          expression.type === "SequenceExpression" ||
-          isBinaryCastExpression(expression) ||
-          isBinaryish(expression))
-      ) {
-        expressionDoc = [indent([softline, expressionDoc]), softline];
-      }
+    // Breaks at the template element boundaries (${ and }) are preferred to breaking
+    // in the middle of a MemberExpression
+    if (
+      interpolationHasNewline &&
+      (hasComment(expression) ||
+        expression.type === "Identifier" ||
+        isMemberExpression(expression) ||
+        expression.type === "ConditionalExpression" ||
+        expression.type === "SequenceExpression" ||
+        isBinaryCastExpression(expression) ||
+        isBinaryish(expression))
+    ) {
+      expressionDoc = [indent([softline, expressionDoc]), softline];
     }
 
     const aligned =

src/language-js/utils/index.js

@@ -420,68 +420,6 @@ const isMemberExpression = skipChainExpression(
   createTypeCheckFunction(["MemberExpression", "OptionalMemberExpression"]),
 );
 
-/**
- *
- * @param {any} node
- * @returns {boolean}
- */
-function isSimpleTemplateLiteral(node) {
-  let expressionsKey = "expressions";
-  if (node.type === "TSTemplateLiteralType") {
-    expressionsKey = "types";
-  }
-  const expressions = node[expressionsKey];
-
-  if (expressions.length === 0) {
-    return false;
-  }
-
-  return expressions.every((expr) => {
-    if (isSimpleAtomicExpression(expr) || isSimpleMemberExpression(expr)) {
-      return true;
-    }
-  });
-}
-
-function isSimpleMemberExpression(
-  node,
-  { maxDepth = Number.POSITIVE_INFINITY } = {},
-) {
-  if (hasComment(node)) {
-    return false;
-  }
-  if (node.type === "ChainExpression") {
-    return isSimpleMemberExpression(node.expression, { maxDepth });
-  }
-  if (!isMemberExpression(node)) {
-    return false;
-  }
-
-  let head = node;
-  let depth = 0;
-  while (isMemberExpression(head) && depth++ <= maxDepth) {
-    if (!isSimpleAtomicExpression(head.property)) {
-      return false;
-    }
-    head = head.object;
-    if (hasComment(head)) {
-      return false;
-    }
-  }
-  return isSimpleAtomicExpression(head);
-}
-
-/**
- * This is intended to return true for small expressions
- * which cannot be broken.
- */
-function isSimpleAtomicExpression(node) {
-  if (hasComment(node)) {
-    return false;
-  }
-  return isLiteral(node) || isSingleWordType(node);
-}
-
 /**
  * Attempts to gauge the rough complexity of a node, for example
  * to detect deeply-nested booleans, call expressions with lots of arguments, etc.
@@ -1209,11 +1147,8 @@ export {
   isPrettierIgnoreComment,
   isRegExpLiteral,
   isSignedNumericLiteral,
-  isSimpleAtomicExpression,
   isSimpleCallArgument,
   isSimpleExpressionByNodeCount,
-  isSimpleMemberExpression,
-  isSimpleTemplateLiteral,
   isSimpleType,
   isStringLiteral,
   isTemplateOnItsOwnLine,

tests/format/js/strings/__snapshots__/jsfmt.spec.js.snap

@@ -415,6 +415,12 @@ and this other one: \${
 which already had a linebreak so can be broken up
 \`;
 
+// https://github.com/prettier/prettier/issues/16114
+message = \`this is a long messsage a simple interpolation without a linebreak \${foo} <- like this\`;
+
+message = \`whereas this messsage has a linebreak in the interpolation \${
+  foo} <- like this\`;
+
 =====================================output=====================================
 foo(
   \`a long string \${1 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3} with expr\`,
@@ -537,6 +543,13 @@ and this other one: \${this(
 which already had a linebreak so can be broken up
 \`;
 
+// https://github.com/prettier/prettier/issues/16114
+message = \`this is a long messsage a simple interpolation without a linebreak \${foo} <- like this\`;
+
+message = \`whereas this messsage has a linebreak in the interpolation \${
+  foo
+} <- like this\`;
+
 ================================================================================
 `;
 
@@ -615,6 +628,12 @@ and this other one: \${
 which already had a linebreak so can be broken up
 \`;
 
+// https://github.com/prettier/prettier/issues/16114
+message = \`this is a long messsage a simple interpolation without a linebreak \${foo} <- like this\`;
+
+message = \`whereas this messsage has a linebreak in the interpolation \${
+  foo} <- like this\`;
+
 =====================================output=====================================
 foo(
   \`a long string \${1 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3 + 2 + 3} with expr\`
@@ -737,5 +756,12 @@ and this other one: \${this(
 which already had a linebreak so can be broken up
 \`;
 
+// https://github.com/prettier/prettier/issues/16114
+message = \`this is a long messsage a simple interpolation without a linebreak \${foo} <- like this\`;
+
+message = \`whereas this messsage has a linebreak in the interpolation \${
+  foo
+} <- like this\`;
+
 ================================================================================
 `;

tests/format/js/strings/template-literals.js

@@ -65,3 +65,9 @@ and this other one: ${
 }
 which already had a linebreak so can be broken up
 `;
+
+// https://github.com/prettier/prettier/issues/16114
+message = `this is a long messsage a simple interpolation without a linebreak ${foo} <- like this`;
+
+message = `whereas this messsage has a linebreak in the interpolation ${
+  foo} <- like this`;