Add a column offset to JSEvalOptions

[andreasrosdal]

An embedder that evaluates a fragment carved out of a larger document — an inline <script>, an event-handler attribute, a snippet extracted from a bundle — can already tell the engine which line the fragment starts on, but not which column. The first line's columns therefore come out relative to the fragment, and stack traces for it do not line up with the document the user is looking at.

Add JSEvalOptions.col_num alongside line_num. js_parse_init() backs both column origins (line_start, eol) up by col - 1, so the first line is numbered from that column and every later line is unaffected — both are reset at the first line terminator. token.line_num also starts at line rather than 1, which it should have all along.

JSEvalOptions o = { .version = JS_EVAL_OPTIONS_VERSION,
                    .filename = "doc.html",
                    .line_num = 1, .col_num = 24 };
JS_EvalThis2(ctx, global, "nope()", 6, &o);
// at <eval> (doc.html:1:24)

On the version bump

This is the first use of the ABI-compatible extension the header describes, so JS_EVAL_OPTIONS_VERSION goes to 2. For that to actually be ABI-compatible the check has to stop demanding the newest version:

-        if (options->version != JS_EVAL_OPTIONS_VERSION)
+        if (options->version < 1 || options->version > JS_EVAL_OPTIONS_VERSION)

A caller built against version 1 then keeps working with its shorter struct, and col_num is only read when the caller says version >= 2. Rejecting an unknown-but-higher version stays as it was. Happy to drop the bump and put col_num in version 1 instead if you would rather not commit to that policy yet — it changes only these few lines.

Testing

Verified with a small C harness that a version-1 struct still evaluates and reports 1:1, that col_num = 1 is byte-for-byte the old behaviour, and that a fragment containing a newline numbers its second line from column 1:

line=1 col=1  -> at <eval> (doc.html:1:1)
line=1 col=24 -> at <eval> (doc.html:1:24)
line=7 col=24 -> at <eval> (doc.html:7:24)
"\n  nope()" with col=24 -> at <eval> (doc.html:2:3)
v1 struct     -> at <eval> (old.js:1:1)

tests.conf — which includes parse-error-column.js and global-reference-column.js — is unchanged, and api-test passes.

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These are 16 PRs from Nordstjernen web browser:

https://github.com/nordstjernen-web/nordstjernen-browser

test262 conformance (the real metric):

┌────────────────────┬────────────────┬─────────────┐
│ │ Known failures │ Conformance │
├────────────────────┼────────────────┼─────────────┤
│ Before │ 52 │ ~99.93% │
├────────────────────┼────────────────┼─────────────┤
│ After all 16 merge │ 18 │ ~99.98% │
└────────────────────┴────────────────┴─────────────┘