[PoC] Gentype emit TS assertions to let TS validate that bindings are correct

[zth]

Papaparse.res:

@gentype.satisfies(("papaparse", "ParseError")) type parseError = { /** A generalization of the error */ @as("type") type_: [#Quotes | #Delimiter | #FieldMismatch], /** Standardized error code */ code: [#MissingQuotes | #UndetectableDelimiter | #TooFewFields | #TooManyFields | #InvalidQuotes], /** Human-readable details */ message: string, /** Row index of parsed data where error is */ row?: int, /** Index within the row where error is */ index?: int, } @gentype.satisfies(("papaparse", "ParseMeta")) type parseMeta = { /** Delimiter used */ delimiter: string, /** Line break sequence used */ linebreak: string, /** Whether process was aborted */ aborted: bool, /** Array of field names */ fields?: array<string>, /** Whether preview consumed all input */ truncated: bool, cursor: float, } @gentype.satisfies(("papaparse", "ParseResult")) type parseResult<'t> = { /**  * an array of rows. If header is false, rows are arrays; otherwise they are objects of data keyed by the field name.  */ data: array<'t>, /** an array of errors. */ errors: array<parseError>, /**  * contains extra information about the parse, such as delimiter used,  * the newline sequence, whether the process was aborted, etc.  * Properties in this object are not guaranteed to exist in all situations.  */ meta: parseMeta, } @gentype.satisfies(("papaparse", "parse")) @module("papaparse") external parseCsvString: string => parseResult<'t> = "parse" 

Emits Papaparse.assertions.ts:

export {}; type $RescriptTypeSatisfiesTypeScriptType<RescriptType extends TypeScriptType, TypeScriptType> = RescriptType; type parseError = $RescriptTypeSatisfiesTypeScriptType<{ /** A generalization of the error */ readonly type: "Delimiter" | "FieldMismatch" | "Quotes"; /** Standardized error code */ readonly code: "TooManyFields" | "MissingQuotes" | "UndetectableDelimiter" | "TooFewFields" | "InvalidQuotes"; /** Human-readable details */ readonly message: string; /** Row index of parsed data where error is */ readonly row?: number; /** Index within the row where error is */ readonly index?: number }, import("papaparse").ParseError>; type parseMeta = $RescriptTypeSatisfiesTypeScriptType<{ /** Delimiter used */ readonly delimiter: string; /** Line break sequence used */ readonly linebreak: string; /** Whether process was aborted */ readonly aborted: boolean; /** Array of field names */ readonly fields?: string[]; /** Whether preview consumed all input */ readonly truncated: boolean; readonly cursor: number }, import("papaparse").ParseMeta>; type parseResult<t> = $RescriptTypeSatisfiesTypeScriptType<{ /** * an array of rows. If header is false, rows are arrays; otherwise they are objects of data keyed by the field name. */ readonly data: t[]; /** an array of errors. */ readonly errors: parseError[]; /** * contains extra information about the parse, such as delimiter used,  * the newline sequence, whether the process was aborted, etc.  * Properties in this object are not guaranteed to exist in all situations. */ readonly meta: parseMeta }, import("papaparse").ParseResult<t>>; const parse = undefined as unknown as typeof import("papaparse").parse satisfies <t>(_1:string) => parseResult<t>;

This lets TypeScript typecheck that the bindings you've written in Papaparse.res is correct.

Very messy code and needs a bunch of cleanup. That can be done if this is an interesting direction that works out in practice.

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commit: eed7f63