sql: relax constraints on VirtualCursor layout
VirtualCursor::FromSqliteCursor required that VirtualCursor had a standard layout, but in fact VirtualCursor shouldn't have a standard layout, and the fact that it does with libc++ is a deviation from the C++ standard. This change: 1. Relaxes the requirement that VirtualCursor has a standard layout, and 2. Relaxes the requirement that the sqlite_cursor_ field has to be at offset 0 by use of offsetof() and pointer subtraction. This change both improves standards compliance and makes this code build with libstdc++. Bug: 1380656 Change-Id: I9c47abd9197b187da0360ca5619ccf7dadab4f33 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4292313 Reviewed-by: Austin Sullivan <asully@chromium.org> Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org> Cr-Commit-Position: refs/heads/main@{#1111925}
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Chromium LUCI CQ

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@ -63,12 +63,10 @@ class VirtualCursor {
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// |sqlite_cursor| must have been returned by VirtualTable::SqliteCursor().
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static inline VirtualCursor* FromSqliteCursor(
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sqlite3_vtab_cursor* sqlite_cursor) {
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static_assert(std::is_standard_layout<VirtualCursor>::value,
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"needed for the reinterpret_cast below");
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static_assert(offsetof(VirtualCursor, sqlite_cursor_) == 0,
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"sqlite_cursor_ must be the first member of the class");
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VirtualCursor* result = reinterpret_cast<VirtualCursor*>(sqlite_cursor);
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DCHECK_EQ(sqlite_cursor, &result->sqlite_cursor_);
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VirtualCursor* result = reinterpret_cast<VirtualCursor*>(
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(reinterpret_cast<char*>(sqlite_cursor) -
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offsetof(VirtualCursor, sqlite_cursor_)));
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CHECK_EQ(sqlite_cursor, &result->sqlite_cursor_);
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return result;
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}
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