[Inlay Hints]

Inferred type annotations on simple assignments — const, series, and input kinds.

Inlay Hints

Abstract

Inlay hints surface inferred types next to simple name = expr assignments when no explicit type annotation is present. Inference is deliberately shallow: constants, bare series builtins (close, …), input.* constructors, and ta/math/str/color calls whose metadata detail contains a → return type. Ambiguous operators are skipped rather than guessed wrong.

Conceptual model

Example mental model (from module docstring):

length = 14                 →  length: const int
rsi = ta.rsi(close, 14)     →  rsi: series float   (from metadata detail)
n = input.int(5, "n")       →  n: input int

Interface surface

  • Method: textDocument/inlayHint
  • Capability: InlayHintOptions(resolve_provider=False)
  • Handler: features/inlay_hints.py → handle_inlay_hints

Each hint:

FieldValue
positionEnd of target identifier (lineno-1, col_offset + len(id))
label": {type_label}"
kindInlayHintKind.Type
tooltipInferred type: {type_label}

Returns [] for empty source, None if parse fails (client typically treats as no hints).

Internals

Constant mapping

Python valueLabel
boolconst bool
intconst int
floatconst float
strconst string

Builtin bare names

open, high, low, close, volume, hl2, hlc3, ohlc4 → series float; time / bar index vars → series int; na → na.

Calls

  • input.{int,float,bool,string,color,symbol,session,source,time,timeframe,price} → input {attr}
  • ta|math|str|color.{attr} → parse detail after →, else fallback "series"

Walk

Recursive over _fields (same pattern as workspace symbol collection) — not limited to script top-level; nested function assigns can receive hints.

PathRole
features/inlay_hints.pyCollection + inference
providers/builtin_metadata.pyReturn-type detail for modules

Invariants and edge cases

  1. Explicit name: type = … suppresses hints (node.type is not None).
  2. Tuple / attribute targets are ignored.
  3. BinOp / Compare / Conditional return None — no speculative arithmetic types.
  4. Metadata quality bounds accuracy — missing → in detail yields coarse series.
  5. No resolve step — tooltips are final.

Worked example

//@version=5
indicator("hints")
length = 14
src = close
avg = ta.sma(src, length)
period = input.int(20, "Period")

Expected hints (when parse + metadata succeed):

  • length → : const int
  • src → : series float
  • avg → type from ta.sma detail (typically series float) or series
  • period → : input int

avg will not get a hint derived from length’s type through the call graph — only the call’s known return shape.

Failure modes

SymptomCause
No hints on fileParse error → None
ta.* always : seriesMetadata detail lacks → segment
Hints mid-identifierIncorrect col_offset on AST node — builder issue

See also