fix(cli): treat json v2 truncated-input error as unexpected EOF (Go 1.27) (#301)

[chiliec]

Fixes #301.

Problem

Go 1.27 backs encoding/json with the v2 implementation. Marshal/unmarshal behavior is preserved, but the exact error values differ. Specifically, when (*json.Decoder).Token() hits a stream that is truncated in the middle of a value, Go ≤1.26 returned io.EOF, while Go 1.27 returns a *json.SyntaxError ("unexpected end of JSON input").

cli/stream.go only recognized io.EOF when converting a mid-structure end-of-input into io.ErrUnexpectedEOF:

if err == io.EOF && s.states[len(s.states)-1] != jsonStateTopValue {
    err = io.ErrUnexpectedEOF
}

On Go 1.27 that check is false, so the raw v2 *json.SyntaxError leaks up to cli/inputs.go, which takes the *json.SyntaxError branch (offset one column earlier) and prints the v2 message. The stream option with unterminated input test then fails:

- 	           ^  unexpected EOF
+ 	          ^  unexpected end of JSON input

Fix

Normalize both representations to io.ErrUnexpectedEOF via a small helper. It keeps the original io.EOF case and additionally accepts a *json.SyntaxError whose offset is at the end of the consumed input (se.Offset >= dec.InputOffset()) — that offset condition is what distinguishes a truncation from a genuine mid-stream syntax error (e.g. [1 2], {"a" bad}), which keep their original error untouched. Because the pre-existing io.ErrUnexpectedEOF path in cli/inputs.go already seeks to end-of-input for the caret, the rendered position and message are now identical across Go versions.

One file changed, no new test needed — the existing stream option with unterminated input golden case is the regression test.

Verification

Ran the full suite on both toolchains (GOTOOLCHAIN=local):

Go 1.27.0 (reproduces the bug without the patch):

• Without fix: --- FAIL: TestCliRun/stream_option_with_unterminated_input
• With fix: ok github.com/itchyny/gojq/cli — go test ./... all green.

Go 1.24.6 (no regression):

• go test ./... → ok github.com/itchyny/gojq and ok github.com/itchyny/gojq/cli.

gofmt -l clean, go vet ./cli/ clean.

Also spot-checked the discriminator directly: truncation inputs ({"a":1,, [1,, {"a":1, [1) all report SyntaxError.Offset == len(input) on Go 1.27 and are normalized; genuine syntax errors ([1 2], {"a" bad}, {"a":@}) have Offset < len and pass through unchanged.

AI assistance disclosure

This change was prepared with an AI coding assistant; the root-cause analysis, fix, and cross-version verification above were all run against real Go 1.24.6 and Go 1.27.0 toolchains, not generated.