From 99b5cef83e3784fd7bbc102c962641c48656b7c8 Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Fri, 15 May 2026 19:37:10 +0200
Subject: [PATCH] Fix stepinfo crash when response never reaches risetime
 thresholds

`stepinfo` indexed `res.t[i10]` / `res.t[i90]` without checking that
`findfirst` actually located the rise-time crossings. For a response
that never crosses the lower or upper threshold within the simulation
window, `findfirst` returns `nothing` and the indexing then raised
`MethodError: no method matching getindex(..., ::Nothing)`.

The function now sets `i10`/`i90` to `0` (sentinel for "not reached"),
sets `risetime = NaN`, and emits a warning. The `stepinfoplot` recipe
skips the rise-time series when either index is zero.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 lib/ControlSystemsBase/src/plotting.jl | 26 ++++++++++++++------------
 lib/ControlSystemsBase/src/timeresp.jl |  9 ++++++++-
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/lib/ControlSystemsBase/src/plotting.jl b/lib/ControlSystemsBase/src/plotting.jl
index 4f5b38ad0..d6f2214dd 100644
--- a/lib/ControlSystemsBase/src/plotting.jl
+++ b/lib/ControlSystemsBase/src/plotting.jl
@@ -175,18 +175,20 @@ end
         label := @sprintf("Final value: %.3f", si.yf)
         [si.yf]
     end
-    @series begin
-        linestyle := :solid
-        linewidth --> 2
-        color --> 2
-        label := @sprintf("Rise time: %.3f", si.risetime)
-        si.res.t[si.i10:si.i90], si.res.y[1, si.i10:si.i90]
-    end
-    @series begin
-        color --> 2
-        seriestype := :vline
-        label := @sprintf("Rise time threshold: %.1f%%-%.1f%%", 100si.risetime_th[1], 100si.risetime_th[2])
-        [si.res.t[si.i10], si.res.t[si.i90]]
+    if si.i10 > 0 && si.i90 > 0
+        @series begin
+            linestyle := :solid
+            linewidth --> 2
+            color --> 2
+            label := @sprintf("Rise time: %.3f", si.risetime)
+            si.res.t[si.i10:si.i90], si.res.y[1, si.i10:si.i90]
+        end
+        @series begin
+            color --> 2
+            seriestype := :vline
+            label := @sprintf("Rise time threshold: %.1f%%-%.1f%%", 100si.risetime_th[1], 100si.risetime_th[2])
+            [si.res.t[si.i10], si.res.t[si.i90]]
+        end
     end
     @series begin
         color --> 3
diff --git a/lib/ControlSystemsBase/src/timeresp.jl b/lib/ControlSystemsBase/src/timeresp.jl
index ccc7fb9e3..806e9a8ac 100644
--- a/lib/ControlSystemsBase/src/timeresp.jl
+++ b/lib/ControlSystemsBase/src/timeresp.jl
@@ -550,7 +550,14 @@ function stepinfo(res::SimResult; y0 = nothing, yf = nothing, settling_th = 0.02
     op = direction == 1 ? (>) : (<)
     i10 = findfirst(op.(y, y0 + risetime_th[1] * stepsize * direction))
     i90 = findfirst(op.(y, y0 + risetime_th[2] * stepsize * direction))
-    risetime = res.t[i90] - res.t[i10]
+    if i10 === nothing || i90 === nothing
+        @warn "Response did not reach the requested risetime threshold(s) within the simulation window"
+        i10 = i10 === nothing ? 0 : i10
+        i90 = i90 === nothing ? 0 : i90
+        risetime = oftype(float(res.t[1]), NaN)
+    else
+        risetime = res.t[i90] - res.t[i10]
+    end
     StepInfo(y0, yf, stepsize, peak, peaktime, overshoot, lowerpeak, lowerpeakind, undershoot, settlingtime, settlingtimeind, risetime, i10, i90, res, settling_th, risetime_th)
 end