Resolve embedded-interface fields in get() builtin (match member access) - #977
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mahirhir wants to merge 1 commit into
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Resolve embedded-interface fields in get() builtin (match member access)#977mahirhir wants to merge 1 commit into
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runtime.Fetch was taught in expr-lang#952 to resolve a field on the concrete type held by an embedded interface, but the sibling builtin get() was left on the old standard-promotion-only lookup. get() is documented to differ from runtime.Fetch only in returning nil instead of panicking, so the same field access returned a value through member access (a.field) yet nil through get(a, "field"). Share the traversal by exporting runtime.FetchFromEmbeddedInterfaces and calling it from get()'s struct branch, mirroring Fetch. Adds a regression test under test/issues/952.
sanmaxdev
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Jul 11, 2026
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The shared lookup keeps get() consistent with member access for fields behind embedded interfaces, while preserving nil for missing fields. The focused package tests and full suite pass.
Checked with:
- go test ./vm/runtime ./builtin ./test/issues/952
- go test ./...
- git diff --check upstream/master...HEAD
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The builtin get(obj, "field") doesn't resolve fields on the concrete type behind an embedded interface, while member access (...).field does. So for a value whose static type is unknown at compile time, (cond ? x : y).Value returns the value but get((cond ? x : y), "Value") returns nil — inconsistent access for the same field.
PR #952 added fetchFromEmbeddedInterfaces to runtime.Fetch but left its sibling get() behind; #935 had previously kept the two in lockstep. The fix mirrors #952's logic into get().
Verified both ways with go test: old returns nil, fixed returns the value; a missing field still returns nil (no panic), zero regression across the suite.