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fix(formatter): preserve inline lambda body alignment #1583

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Merged
Lorenzobattistela merged 2 commits into from
Oct 15, 2026
Merged

fix(formatter): preserve inline lambda body alignment #1583

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4a58279
fix(formatter): preserve inline lambda body alignment
vicmcorrea Oct 15, 2026
8819cd9
fix(formatter): only pin after a top-level =>
Lorenzobattistela Oct 15, 2026
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6 changes: 4 additions & 2 deletions tools/bend-fmt-lsp/src/formatter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -164,14 +164,16 @@ function looseLines(lines: Line[]): boolean[] {
}

// The tokens that start a body on the line of its `do`, `match`, `case` or
// `def` header, as in `do IO<Unit>: a`: Bend pins the lines after it to the
// column of `a`.
// `def` header or `=>` lambda opener. As in `do IO<Unit>: a`, Bend pins the
// lines after it to the column of `a`.
function inlineBodies(lines: Line[]): number[][] {
let open = 0;
let header: { open: number; angle: number; typed: boolean } | null = null;
return lines.map((line) => line.tokens.flatMap((token, index) => {
if (token.kind === "word" && ["do", "match", "case", "def"].includes(token.text)) {
header = { open, angle: 0, typed: token.text === "do" || token.text === "def" };
} else if (token.text === "=>" && open === 0) {
return index + 1 < line.tokens.length ? [index + 1] : [];
} else if (["(", "[", "{"].includes(token.text)) {
open++;
} else if ([")", "]", "}"].includes(token.text)) {
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6 changes: 5 additions & 1 deletion tools/bend-fmt-lsp/src/test/formatter.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,12 @@ import { fileURLToPath } from "node:url";
import { formatBend } from "../formatter.js";

// Bend pins the lines after a body that shares a line with its `do`, `match`,
// `case` or `def` header to that body's column. [source, formatted]
// `case` or `def` header or `=>` lambda opener to that body's column. [source, formatted]
const pinned = [
[
"import Base\ndef main() -> Array<U32>:\n f : Array<U32> -> Array<U32> = a => a[0] <- 7\n a[1] <- 8\n f([0 : U32 * 2n])\n",
"import Base\ndef main() -> Array<U32>:\n f : Array<U32> -> Array<U32> = a => a[0] <- 7\n a[1] <- 8\n f([0 : U32 * 2n])\n",
],
[
"import Base\ndef main() -> IO(Unit):\n do IO<Unit>: IO.print(\"a\")\n IO.print(\"b\")\n",
"import Base\ndef main() -> IO(Unit):\n do IO<Unit>: IO.print(\"a\")\n IO.print(\"b\")\n",
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