Fix md_parse_sequence_points document and rolling value bugs

[AaronRobinsonMSFT]

Problem

Two bugs in md_parse_sequence_points():

Bug 1: Document cursor not set from row column

When the MethodDebugInformation row has a non-null Document column (the common case for single-document methods), the parser reads it into a local document cursor but never copies it to sequence_points->document. The field is left at the invalid row-0 default from create_cursor(&cxt->tables[mdtid_Document], 0), causing callers that try to resolve the document name to fail.

Bug 2: Rolling values not accumulated

The rolling_il_offset, rolling_start_line, and rolling_start_column fields store raw blob values instead of accumulated running sums. The Portable PDB spec delta-encodes these values — the first record is absolute, subsequent records are signed deltas from the previous — but the parser stored the raw deltas. This caused incorrect source locations for any sequence point after the first in a method.

Example: A method starting at line 69 with sequence points at lines 69, 70, 71 would instead report lines 69, 1, 1 (the raw deltas).

Fix

1. When the Document column is non-null, use the cursor directly as sequence_points->document.
2. Maintain running_il, running_line, and running_col accumulators across the record loop.

[AaronRobinsonMSFT]

Updated: The force-pushed commit now fixes a second bug in the same function — the rolling_il_offset, rolling_start_line, and rolling_start_column fields were storing raw deltas instead of accumulated running sums. This caused incorrect source locations for any sequence point after the first in a method (e.g., line 69 → 70 → 71 would report as 69 → 1 → 1).

[Copilot]

Pull request overview

Fixes Portable PDB SequencePoints parsing so md_parse_sequence_points() correctly sets the initial document cursor from the MethodDebugInformation.Document column (the common single-document case), aligning behavior with the Portable PDB spec.

Changes:

• Set sequence_points->document from the non-null MethodDebugInformation.Document column; only read InitialDocument from the blob when the column is null.
• Accumulate delta-encoded ILOffset/StartLine/StartColumn into rolling (absolute) values for output records.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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[AaronRobinsonMSFT]

@jkoritzinsky I'm going to commit this to unblock myself. If this doesn't make sense to you, we can revert and put up a proper fix. We should do some brain storming on testing shortly though.

[jkoritzinsky]

Yeah we don't have a good testing story for the portable PDB blob formats at the moment.