RFC: label doc (#10275)

* RFC: label doc

* Update functions in doc-utils

commands.md

@@ -271,6 +271,18 @@ With `negate: true`, corresponds to `ifBreak(doc, indent(doc), { groupId })`
 
 It doesn't make sense to apply `indentIfBreak` to the current group because "indent if the current group is broken" is the normal behavior of `indent`. That's why `groupId` is required.
 
+### `label`
+
+_Added in v2.3.0_
+
+```ts
+declare function label(label: string, doc: Doc): Doc;
+```
+
+Mark a doc with a string label. This doesn't affect how the doc is printed, but can be useful for heuristics based on doc introspection.
+
+E.g., to decide how to print an assignment expression, we might want to know whether its right-hand side has been printed as a method call chain, not as a plain function call. If the method chain printing code uses `label` to mark its result, checking that condition can be as easy as `rightHandSideDoc.label === 'method-chain'`.
+
 ### `hardlineWithoutBreakParent` and `literallineWithoutBreakParent`
 
 _Added in v2.3.0_

src/document/doc-builders.js

@@ -259,6 +259,10 @@ function addAlignmentToDoc(doc, size, tabWidth) {
   return aligned;
 }
 
+function label(label, contents) {
+  return { type: "label", label, contents };
+}
+
 module.exports = {
   concat,
   join,
@@ -284,4 +288,5 @@ module.exports = {
   dedent,
   hardlineWithoutBreakParent,
   literallineWithoutBreakParent,
+  label,
 };

src/document/doc-debug.js

@@ -173,6 +173,10 @@ function printDocToDebug(doc) {
       return "lineSuffixBoundary";
     }
 
+    if (doc.type === "label") {
+      return `label(${JSON.stringify(doc.label)}, ${printDoc(doc.contents)})`;
+    }
+
     throw new Error("Unknown doc type " + doc.type);
   }
 

src/document/doc-printer.js

@@ -258,6 +258,9 @@ function fits(next, restCommands, width, options, hasLineSuffix, mustBeFlat) {
             return false;
           }
           break;
+        case "label":
+          cmds.push([ind, mode, doc.contents]);
+          break;
       }
     }
   }
@@ -553,6 +556,9 @@ function printDocToString(doc, options) {
               break;
           }
           break;
+        case "label":
+          cmds.push([ind, mode, doc.contents]);
+          break;
         default:
       }
     }

src/document/doc-utils.js

@@ -227,8 +227,10 @@ function stripDocTrailingHardlineFromDoc(doc) {
   switch (doc.type) {
     case "align":
     case "indent":
+    case "indent-if-break":
     case "group":
-    case "line-suffix": {
+    case "line-suffix":
+    case "label": {
       const contents = stripDocTrailingHardlineFromDoc(doc.contents);
       return { ...doc, contents };
     }
@@ -270,6 +272,7 @@ function cleanDocFn(doc) {
       break;
     case "align":
     case "indent":
+    case "indent-if-break":
     case "line-suffix":
       if (!doc.contents) {
         return "";

src/language-js/print/member-chain.js

@@ -24,7 +24,15 @@ const {
 const { locEnd } = require("../loc");
 
 const {
-  builders: { join, hardline, group, indent, conditionalGroup, breakParent },
+  builders: {
+    join,
+    hardline,
+    group,
+    indent,
+    conditionalGroup,
+    breakParent,
+    label,
+  },
   utils: { willBreak },
 } = require("../../document");
 const printCallArguments = require("./call-arguments");
@@ -374,6 +382,8 @@ function printMemberChain(path, options, print) {
     );
   }
 
+  let result;
+
   // We don't want to print in one line if at least one of these conditions occurs:
   //  * the chain has comments,
   //  * the chain is an expression statement and all the arguments are literal-like ("fluent configuration" pattern),
@@ -389,16 +399,18 @@ function printMemberChain(path, options, print) {
     printedGroups.slice(0, -1).some(willBreak) ||
     lastGroupWillBreakAndOtherCallsHaveFunctionArguments()
   ) {
-    return group(expanded);
+    result = group(expanded);
+  } else {
+    result = [
+      // We only need to check `oneLine` because if `expanded` is chosen
+      // that means that the parent group has already been broken
+      // naturally
+      willBreak(oneLine) || shouldHaveEmptyLineBeforeIndent ? breakParent : "",
+      conditionalGroup([oneLine, expanded]),
+    ];
   }
 
-  return [
+  return label("member-chain", result);
-    // We only need to check `oneLine` because if `expanded` is chosen
-    // that means that the parent group has already been broken
-    // naturally
-    willBreak(oneLine) || shouldHaveEmptyLineBeforeIndent ? breakParent : "",
-    conditionalGroup([oneLine, expanded]),
-  ];
 }
 
 module.exports = printMemberChain;

tests_integration/__tests__/debug-api.js

@@ -66,6 +66,7 @@ describe("API", () => {
       indentIfBreak,
       group,
       line,
+      label,
     } = builders;
 
     expect(formatDoc([indent(hardline), indent(literalline)])).toBe(
@@ -86,5 +87,9 @@ describe("API", () => {
     expect(
       formatDoc(indentIfBreak(group(["1", line, "2"]), { groupId: "Q" }))
     ).toBe('indentIfBreak(group(["1", line, "2"]), { groupId: "Q" })');
+
+    expect(formatDoc(label("foo", group(["1", line, "2"])))).toBe(
+      'label("foo", group(["1", line, "2"]))'
+    );
   });
 });