thrift-ls

thrift-ls

A Thrift language server, formatter, and linter.

Fork notice. This project is a fork of joyme123/thrift-ls, an Apache-2.0 Thrift language server and formatter. The lexer and CST parser were rewritten from scratch, the formatter is a complete rewrite, and the LSP was overhauled; the upstream copyright is retained in NOTICE.

• Language server: completion, go to definition, find references, hover, diagnostics, rename, document symbols, and formatting — including range formatting (Format Selection).
• Formatter: a full rewrite of the old template-based formatter. It is lossless (comments, annotations, and blank lines survive everywhere), width-aware, deterministic, and idempotent — properties enforced by fuzzing.
• Linter: thrift-ls check runs the full diagnostic pipeline, fix code actions from the editor

Installation

go install github.com/karitham/thrift-ls@latest

This installs the thrift-ls binary. It speaks LSP over stdio and doubles as a CLI formatter.

Prebuilt binaries (linux/darwin/windows, amd64/arm64) and a VS Code extension (thrift-ls-<version>.vsix) are attached to GitHub releases.

nix run github:karitham/thrift-ls runs the flake package.

Usage

thrift-ls [flags]            run the language server (default)
thrift-ls lsp [flags]        run the language server
thrift-ls format [flags] <file>   format a thrift file
thrift-ls dump [--ir|--includes] <file>   dump the parse tree, formatter IR, or include resolution

Run thrift-ls --help or thrift-ls format --help for the full flag list.

As a language server

thrift-ls is a plain LSP server speaking JSON-RPC over stdio. No editor extension is required: any LSP client can attach to the binary directly.

thrift-ls

or, explicitly:

thrift-ls lsp

helix

Helix ships a thrift language definition, so only the server and the attachment are needed in ~/.config/helix/languages.toml:

[language-server.thrift-ls]
command = "thrift-ls"

[[language]]
name = "thrift"
language-servers = ["thrift-ls"]
# optional: format on save via the LSP
auto-format = true

thrift-ls must be on PATH, or use an absolute path as command. The server logs to $TMPDIR/thrift-ls.log and, once the LSP handshake is done, forwards its records to the client as window/logMessage (the editor's LSP log or output channel); raise verbosity with -logLevel.

neovim

nvim-lspconfig ships a thriftls entry, named after the upstream project this is a fork of. Point it at the thrift-ls binary:

require("lspconfig").thriftls.setup({ cmd = { "thrift-ls" } })

MasonInstall thriftls and nixvim's thriftls package install the upstream server, not this one — prefer go install, a release binary, or the flake.

vim

Use thrift-ls as the LSP provider for thrift files:

let g:lsp_settings = { 'thrift': { 'cmd': ['thrift-ls'] } }

vscode

Install the thrift-ls-<version>.vsix from the releases page, or run the extension from source (vscode/). The extension is a thin LSP client: it finds thrift-ls on PATH (or via the thrift-ls.path setting), and offers to download the matching release binary on first use. Formatting — whole document, selection, and on-type — works through the server, so format-on-save needs no extra setup.

As a formatter

# print the formatted file to stdout
thrift-ls format path/to/file.thrift

# overwrite the file in place
thrift-ls format -w path/to/file.thrift

# print a diff instead
thrift-ls format -d path/to/file.thrift

# batch-format a tree
find . -name "*.thrift" | xargs -n 1 thrift-ls format -w

Formatting flags:

Flags override the config file.

Debugging: dump

thrift-ls dump prints the parse tree — every token with its position, blank-line count, and attached comment trivia, plus the node spans — which is useful to understand how the lexer attached a comment or why the formatter moved something:

thrift-ls dump path/to/file.thrift

With --ir, it also builds the formatter's document IR, prints it (which records the layout decisions on the groups), and dumps the IR tree showing which groups broke and which stayed flat:

thrift-ls dump --ir --printWidth 100 path/to/file.thrift

With --includes, it shows how every include of the file resolves instead of dumping the tree: the chosen location, whether it parses, and every other include path the include also matches. Pass --logLevel 5 to dump or check to route the pipeline's debug log (resolver decisions, unreadable definition files, parse errors) to stderr:

thrift-ls dump --includes path/to/file.thrift
thrift-ls check --logLevel 5 path/to/file.thrift

Diagnostics: check

thrift-ls check runs the same diagnostic pipeline the language server uses — parse, semantic analysis, and lints — over a file or a whole folder, and reports everything to stdout. It exits 1 when any error-severity diagnostic is found, so it can gate CI:

thrift-ls check path/to/file.thrift    # one file
thrift-ls check path/to/folder/        # every *.thrift under the folder

Output is one line per diagnostic:

lints.thrift:37:1  warning  unused include "unused.thrift"
lints.thrift:132:10  warning  map key must be a scalar type, found struct

The checks:

Code actions (refactors and quickfixes) fix these from the editor:

• Make enum values explicit — fills in the implicit enum values.
• Make field required / optional — rewrites the field qualifier.
• Remove unused include — deletes the include line (quickfix on the warning).
• Add include "x.thrift" — finds the file defining a missing type anywhere in the workspace and adds the include (quickfix on field type doesn't exist).

Formatter behavior

The formatter is lossless: comments, @ annotations, and blank lines survive formatting everywhere — including comments inside container types (map<string, /* c */ i32>), const values, and annotation parens. The formatted output re-parses cleanly and formatting is idempotent and deterministic; comment preservation, idempotency, and parseability are enforced by a fuzzer over the full option space.

Conditional breaking, zig-style

Like zig fmt, a trailing delimiter on the last item of a list decides whether the list folds:

struct S {
  1: i32 a;
  2: string b;
}

stays multiline because the source ends the last field with ;, while

struct S {
  1: i32 a
  2: string b
}

folds to struct S { 1: i32 a 2: string b } when it fits. The rule applies to struct/union/exception bodies, enum bodies, function arguments, and throws clauses. The break.* options force the multiline layout regardless of the source.

Note: a trailing delimiter only forces the multiline layout when the separator mode actually emits it — remove drops separators, so it cannot force a break (the output would not round-trip).

Width-aware folding

Every group — struct bodies, function signatures, argument lists, throws clauses, const lists, annotations — decides independently whether it fits in the remaining width at its position. In particular, arguments and throws fold independently:

service Processor {
  string upload(
    1: string               imageUrl,
    2: arguments.Size       size,
    3: arguments.Identifier id,
  ) throws (1: errors.ProcessingError err)
}

The arguments break (trailing commas), while the throws clause stays flat because it fits on the closing paren's line. Comments or blank lines inside a clause force it to break, without breaking the other clause.

Column alignment

Struct/union/exception fields and enum values are column-aligned within their group (align: field). Alignment groups split at blank lines and comments, like whitespace. A group is aligned only when the padded columns fit within printWidth — except layouts that were deliberately column-aligned in the source, which are preserved even when they overflow. Trailing comments may overflow their line without affecting alignment.

Configuration

Configuration lives in a thrift-ls.json file, discovered by walking up from the file being formatted or the workspace root (like Biome). Set the THRIFT_LS_CONFIG env var to point at an explicit config file. In the LSP, discovery happens per workspace folder when the server starts: each folder formats with the nearest thrift-ls.json walking up from it, and a single-file session discovers from the opened file's directory. An explicit --config flag pins one file for every folder (the first folder's config also sets the process-wide log level).

Layered from lowest to highest precedence: defaults, the config file, CLI flags, LSP workspace settings. The VS Code extension exposes the formatter options as thrift-ls.* settings (see vscode/README.md), which override the config file and CLI flags for LSP formatting; includePaths and logLevel are not available as settings — use the config file or flags for those.

{
  "printWidth": 100,
  "indent": "  ",
  "tabWidth": 4,
  "align": "field",
  "separators": {
    "structs": "semicolon",
    "unions": "semicolon",
    "exceptions": "semicolon",
    "enums": "comma",
    "arguments": "comma",
    "throws": "comma",
    "lists": "comma",
    "maps": "comma",
    "sets": "comma"
  },
  "break": {
    "structs": true,
    "unions": true,
    "exceptions": true,
    "enums": true,
    "lists": true,
    "maps": true,
    "sets": true
  },
  "includePaths": ["/path/to/base"],
  "logLevel": 3
}

printWidth

Target line width for breaking decisions. Groups (struct bodies, function signatures, lists, annotations) stay on one line when they fit and break otherwise, each deciding independently based on the remaining width at its position. Default: 80.

indent

Indentation is a literal string of spaces or tabs, e.g. " " or "\t". Default: " " (four spaces).

tabWidth

Display width of a tab when measuring line width. Default: 4.

align

Controls column alignment of struct/union/exception fields and enum values.

• field: Align field IDs, requiredness, and types (default)
• assign: Align the = sign for default values
• disable: No alignment

See Column alignment for how alignment interacts with width, comments, and blank lines.

separators

Controls trailing separators per construct, independently. The separators object has one key per construct: structs, unions, exceptions, enums, arguments (function arguments), throws (throws entries), lists and maps (const list and map values). Each accepts:

• comma: Always add trailing commas
• semicolon: Always add trailing semicolons
• none: Remove trailing separators
• preserve: Keep as written (default)

For lists and maps, the separator appears between the items and after the last item; none removes them entirely ([1, 2] becomes [1 2]). For example, semicolons in structs and commas in enums:

"separators": {
  "structs": "semicolon",
  "unions": "semicolon",
  "exceptions": "semicolon",
  "enums": "comma"
}

Broken (multiline) argument and throws blocks are column-aligned like struct fields, controlled by align.

The separator mode also interacts with conditional breaking: a mode that keeps or adds trailing separators (preserve, comma, semicolon) lets a source trailing delimiter force the multiline layout, while none always folds when the group fits. Under preserve, a mixed separator pattern (some fields separated, some not) also forces the multiline layout — a flat line whose separators are inconsistently present looks broken.

break

Forces layouts that would otherwise collapse to one line to stay multiline, regardless of the source's trailing delimiters. Like separators, the break object has one key per construct: structs, unions, exceptions, enums, arguments, throws, lists, maps.

All default to false.

includePaths

List of additional paths to search for included thrift files. When a thrift file uses include "foo.thrift", thrift-ls first tries to resolve it relative to the current file's directory. If not found, it searches each path in includePaths in order. This is similar to Apache Thrift's -I flag.

logLevel

Controls logging verbosity (the server logs to $TMPDIR/thrift-ls.log):

• 1: fatal
• 2: error
• 3: warn (default)
• 4: info
• 5: debug
• 6: trace

Releasing

A v* tag triggers the release workflow: it builds the six thrift-ls binaries (linux/darwin/windows × amd64/arm64), a checksums.txt, and the VS Code .vsix, attached to the GitHub release. The workflow injects the tag into the binary (--version), and fails if the vsix version doesn't match the tag.

Every push to main also publishes a prerelease per commit (tagged with the commit SHA, binaries report dev-<sha>). Prereleases never become releases/latest, so the extension's downloader keeps serving tagged releases.

Before tagging, make sure the versions agree:

• vscode/package.json version
• flake.nix version and the ServerVersion ldflag (the workflow enforces the vsix; the flake is manual)

git tag v0.1.0 && git push origin v0.1.0

Development

go test ./...   # unit, golden, and fuzz regression tests

The formatter golden tests in formatter/file_test.go pin the formatter options against committed outputs in tests/e2e. The check lint corpus test in check_test.go covers tests/made-in-abyss. The formatter is fuzz-tested end to end: FuzzFormat checks that any clean document formats without errors, keeps every comment, is idempotent and deterministic across the whole option space. The lexer, parser, doc printer, LSP offset mapper, and range formatting each have their own fuzz targets; the corpus entries under testdata/fuzz are permanent regression tests.

thrift-ls dump (see above) is the debugging companion: it shows the parse tree and the formatter's document IR with the layout decisions, so a formatting issue can be pinned to the parser, the IR construction, or the printer.