From 8bed145e0e91f03b0ab9fdbc44cfbdda4a44cd06 Mon Sep 17 00:00:00 2001
From: Nathan Daly <nhdaly@gmail.com>
Date: Sat, 23 Jan 2021 20:53:52 -0500
Subject: [PATCH] Restore StackOverflow error message for repeated frames

Fixes backtrace printing to display the number of times a frame is
repeated, if there is a frame that's duplicated several times.

```julia
julia> function foo() foo() end
foo (generic function with 1 method)

julia> foo()
ERROR: StackOverflowError:
Stacktrace:
 [1] foo() (repeats 79984 times)
   @ Main ./REPL[16]:1
```

Fixes #37587.
---
 base/errorshow.jl | 13 ++++++-------
 test/errorshow.jl | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/base/errorshow.jl b/base/errorshow.jl
index 50325be8354e5..2d7a81b0ccf63 100644
--- a/base/errorshow.jl
+++ b/base/errorshow.jl
@@ -573,17 +573,17 @@ stacktrace_linebreaks()::Bool =
     tryparse(Bool, get(ENV, "JULIA_STACKTRACE_LINEBREAKS", "false")) === true
 
 function show_full_backtrace(io::IO, trace::Vector; print_linebreaks::Bool)
-    n = length(trace)
-    ndigits_max = ndigits(n)
+    num_frames = length(trace)
+    ndigits_max = ndigits(num_frames)
 
     modulecolordict = copy(STACKTRACE_FIXEDCOLORS)
     modulecolorcycler = Iterators.Stateful(Iterators.cycle(STACKTRACE_MODULECOLORS))
 
     println(io, "\nStacktrace:")
 
-    for (i, frame) in enumerate(trace)
-        print_stackframe(io, i, frame, 1, ndigits_max, modulecolordict, modulecolorcycler)
-        if i < n
+    for (i, (frame, n)) in enumerate(trace)
+        print_stackframe(io, i, frame, n, ndigits_max, modulecolordict, modulecolorcycler)
+        if i < num_frames
             println(io)
             print_linebreaks && println(io)
         end
@@ -782,8 +782,7 @@ function show_backtrace(io::IO, t::Vector)
 
     try invokelatest(update_stackframes_callback[], filtered) catch end
     # process_backtrace returns a Vector{Tuple{Frame, Int}}
-    frames = map(x->first(x)::StackFrame, filtered)
-    show_full_backtrace(io, frames; print_linebreaks = stacktrace_linebreaks())
+    show_full_backtrace(io, filtered; print_linebreaks = stacktrace_linebreaks())
     return
 end
 
diff --git a/test/errorshow.jl b/test/errorshow.jl
index 30c7d61bdadde..6ecb529cf3f5f 100644
--- a/test/errorshow.jl
+++ b/test/errorshow.jl
@@ -678,6 +678,7 @@ end
     @test getline(outputc) == getline(output0) + 2
 end
 
+
 # issue #30633
 @test_throws ArgumentError("invalid index: \"foo\" of type String") [1]["foo"]
 @test_throws ArgumentError("invalid index: nothing of type Nothing") [1][nothing]
@@ -763,3 +764,27 @@ let err = nothing
         @test !occursin("2d", err_str)
     end
 end
+
+single_repeater() = single_repeater()
+pair_repeater_a() = pair_repeater_b()
+pair_repeater_b() = pair_repeater_a()
+
+@testset "repeated stack frames" begin
+    let bt = try single_repeater()
+        catch
+            catch_backtrace()
+        end
+        bt_str = sprint(Base.show_backtrace, bt)
+        m = @__MODULE__
+        @test occursin(r"repeats \d+ times", bt_str)
+    end
+
+    let bt = try pair_repeater_a()
+        catch
+            catch_backtrace()
+        end
+        bt_str = sprint(Base.show_backtrace, bt)
+        m = @__MODULE__
+        @test occursin(r"the last 2 lines are repeated \d+ more times", bt_str)
+    end
+end