encoding/jsonschema: wrap comment lines

Change-Id: I482ab0266c66f226490cb93d385da5f34d7f48d2
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5650
Reviewed-by: roger peppe <rogpeppe@gmail.com>

encoding/jsonschema/testdata/basic.txtar

@@ -10,30 +10,31 @@
     "person": {
       "description": "A person is a human being.",
       "type": "object",
-	  "required": [ "name" ],
+      "required": [ "name" ],
       "properties": {
         "name": { "type": "string" },
-		"address": {
-			"description": "where does this person live?",
-			"type": "string"
-		},
+        "address": {
+            "description": "where does this person live?",
+            "type": "string"
+        },
         "children": {
+          "description": "A very large comment that will be wrapped after a certain line length. Let's keep on going and see what happens.",
           "type": "array",
           "items": { "type": "string" },
           "default": []
         },
-		"home phone": {
-			"type": "string",
-			"deprecated": true
-		}
+        "home phone": {
+            "type": "string",
+            "deprecated": true
+        }
       }
     }
   }
 }
 
 -- out.cue --
 // Main schema
-// 
+//
 // Specify who you are and all.
 Schema :: _ @jsonschema(schema="http://json-schema.org/draft-07/schema#")
 Schema :: {
@@ -43,6 +44,9 @@ Schema :: {
 
 		// where does this person live?
 		address?: string
+
+		// A very large comment that will be wrapped after a certain line
+		// length. Let's keep on going and see what happens.
 		children?: [...string]
 		"home phone"?: string @deprecated()
 		...

internal/internal.go

@@ -127,9 +127,28 @@ func NewComment(isDoc bool, s string) *ast.CommentGroup {
 	}
 	scanner := bufio.NewScanner(strings.NewReader(s))
 	for scanner.Scan() {
-		cg.List = append(cg.List, &ast.Comment{Text: "// " + scanner.Text()})
+		scanner := bufio.NewScanner(strings.NewReader(scanner.Text()))
+		scanner.Split(bufio.ScanWords)
+		const maxRunesPerLine = 66
+		count := 2
+		buf := strings.Builder{}
+		buf.WriteString("//")
+		for scanner.Scan() {
+			s := scanner.Text()
+			n := len([]rune(s)) + 1
+			if count+n > maxRunesPerLine && count > 3 {
+				cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
+				count = 3
+				buf.Reset()
+				buf.WriteString("//")
+			}
+			buf.WriteString(" ")
+			buf.WriteString(s)
+			count += n
+		}
+		cg.List = append(cg.List, &ast.Comment{Text: buf.String()})
 	}
-	if last := len(cg.List) - 1; cg.List[last].Text == "// " {
+	if last := len(cg.List) - 1; cg.List[last].Text == "//" {
 		cg.List = cg.List[:last]
 	}
 	return cg