Function infer_structural_clock 

pub fn infer_structural_clock<'d>(
    block: &Symbol<'d>,
) -> Result<Option<TimingControl<'d>>, AnalysisError>

LRM 16.14.6 (a)/(b)/(c) for a procedure that slang’s analysis does not list: one inside a procedural checker instance’s body (17.3). slang analyzes such a body as a side effect of analyzing the enclosing procedure and files no scope result for it, so infer_procedural_clock has no AnalyzedProcedure to ask (and an AnalyzedAssertion::procedure handle into that scope is not safe to follow: slang keeps the procedures in a std::vector and the assertions point into it before it has finished growing). This is therefore the one place the three conditions are decided here rather than by slang, mirroring DFAResults::inferClock for the shapes a checker’s procedure can take:

• (a) no blocking timing control: a delay, wait, or a timing control on anything but a statement makes the answer None (the last is an error here instead, since a = #1 b is not modelled by this walk);
• (b) exactly one event control (a nonblocking assignment’s does not count);
• (c) exactly one edge expr [iff cond] event of it none of whose terms is referenced anywhere else in the procedure other than inside assertion statements or as a clocking event.

An event control that is not of the edge expr form (an event variable, a clocking block name, @*) is an error rather than a guess, since that path would need the event-variable and clocking-block rules of (c) as well.

Unlike infer_procedural_clock, a None means only that the procedure itself yields no clock; the default clocking (16.15) is for the caller.