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runtime: ignore blank fields when comparing structs in interfaces - #5880
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…data The blank-field equality fix in PR tinygo-org#5880 used Field to check each field name. That call returned metadata that the comparison did not need and increased stack use enough to cause a stack overflow on AVR. A field name lookup should not require the same stack space as a full metadata lookup. Keep this prerequisite separate from the equality fix so each change can be reviewed on its own. This commit does not change interface equality. The runtime caller and its equality regression tests remain separate work.
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The Go spec says that two struct values are equal if their corresponding non-blank fields are equal. The compiler already skips blank fields for a direct struct comparison, but the runtime compared all fields when the struct values were held in interfaces. This came from the upstream test/blank.go test, where two struct values that differ only in a blank field compared as not equal.
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The Go spec says that two struct values are equal if their corresponding non-blank fields are equal. The compiler already skips blank fields for a direct struct comparison, but the runtime compared all fields when the struct values were held in interfaces. This came from the upstream test/blank.go test, where two struct values that differ only in a blank field compared as not equal.
The struct comparison in the runtime is recursive and gets the name of each field from RawType.Field. Before #5884, TestBuild/AVR/interface.go failed with "goroutine stack overflow" on the 384-byte simavr goroutine stack. #5884 has merged and this PR is rebased on dev.
RawType.Field still allocates its one-element Index slice, so each struct field in an interface comparison causes one allocation. If this is a problem, a separate change can remove it.