proposal: go/types: publish Error.{Start,End} fields

[adonovan]

Background: Since go1.16 (#42290), go/types has internally recorded three positions (start, pos, and end) for type errors. However, only the Pos field is exposed. The x/tools repo has long resorted to unsavory hacks such as reading the non-exported fields, and using heuristics on the source text (!) to guess the end position.

Proposal: We propose to publish the Start and End fields.

package types

type Error struct {
	Fset       *token.FileSet // file set for interpretation of Pos
	// Invariant: Start <= Pos < End || Start == Pos == End.
	Pos        token.Pos      // error position
+	Start, End token.Pos 	  // start, end of containing expression
	Msg        string         // error message
	Soft       bool           // if set, error is "soft"
}

@gri @findleyr

[gabyhelp]

Related Issues

• go/types, x/tools/gopls: improve the positioning of type checker errors #42290 (closed)

Related Code Changes

• go/types: add unexported start and end positions to type checker errors

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[gopherbot]

Change https://go.dev/cl/650217 mentions this issue: gopls/internal/analysis: simplify type-error analyzers with Cursor