Add iterLines to Text interface

src/text.ts

@@ -104,6 +104,23 @@ export abstract class Text implements Iterable<string> {
   /// iterator will run in reverse.
   iterRange(from: number, to: number = this.length): TextIterator { return new PartialTextCursor(this, from, to) }
 
+  /// Return a cursor that iterates over the given range of lines,
+  /// _without_ returning the line breaks between, and yielding empty
+  /// strings for empty lines.
+  ///
+  /// When `from` and `to` are given, they should be 1-based line numbers.
+  iterLines(from?: number, to?: number) {
+    let inner
+    if (from == null) {
+      inner = this.iter()
+    } else {
+      if (to == null) to = this.lines + 1
+      let start = this.line(from).from
+      inner = this.iterRange(start, Math.max(start, to == this.lines + 1 ? this.length : to <= 1 ? 0 : this.line(to - 1).to))
+    }
+    return new LineCursor(inner)
+  }
+
   /// @internal
   abstract decompose(from: number, to: number, target: Text[], open: Open): void
 
@@ -466,6 +483,35 @@ class PartialTextCursor implements TextIterator {
   get lineBreak() { return this.cursor.lineBreak && this.value != "" }
 }
 
+class LineCursor implements TextIterator {
+  afterBreak = true
+  value = ""
+  done = false
+
+  constructor(readonly inner: TextIterator) {}
+
+  next(skip = 0) {
+    let {done, lineBreak, value} = this.inner.next(skip)
+    if (done) {
+      this.done = true
+      this.value = ""
+    } else if (lineBreak) {
+      if (this.afterBreak) {
+        this.value = ""
+      } else {
+        this.afterBreak = true
+        this.next()
+      }
+    } else {
+      this.value = value
+      this.afterBreak = false
+    }
+    return this
+  }
+
+  get lineBreak() { return false }
+}
+
 /// This type describes a line in the document. It is created
 /// on-demand when lines are [queried](#text.Text.lineAt).
 export class Line {

test/test-text.ts

@@ -165,6 +165,21 @@ describe("Text", () => {
     ist(doc0.iterRange(doc0.length - 2, doc0.length - 1).next().value, "9")
   })
 
+  it("can iterate over lines", () => {
+    let doc = Text.of(["ab", "cde", "", "", "f", "", "g"])
+    function get(from?: number, to?: number) {
+      let result = []
+      for (let i = doc.iterLines(from, to); !i.next().done;) result.push(i.value)
+      return result.join("\n")
+    }
+    ist(get(), "ab\ncde\n\n\nf\n\ng")
+    ist(get(1, doc.lines + 1), "ab\ncde\n\n\nf\n\ng")
+    ist(get(2, 3), "cde")
+    ist(get(1, 1), "")
+    ist(get(2, 1), "")
+    ist(get(3), "\n\nf\n\ng")
+  })
+
   it("can convert to JSON", () => {
     for (let i = 0; i < 200; i++) lines.push("line " + i)
     let text = Text.of(lines)