Why is Emacs Entering the Debugger despite a condition case wrapper?

Question

The context of my question: I was editing some clojure code, and point was inside a comment, and to the right of three characters: `abc'.

I ran the command: M-x company-diag, to ask company mode for a diagnosis of the current company configuration.

Emacs entered the debugger. My question is: Why did emacs enter the debugger?

From the documentation for debug-on-error:

Non-nil means enter debugger if an error is signaled.
Does not apply to errors handled by ‘condition-case’ or those
matched by ‘debug-ignored-errors’.

Although the value of debug-on-error is t, the code which signals the error is wrapped in a condition-case. Why didn't this wrapper prevent the debugger from being entered?

Here is the stack trace. Note that I have annotated this stack trace to indicate the condition case wrapping.

Debugger entered--Lisp error: (void-function clojure\.lang\.ExceptionInfo:)
  clojure\.lang\.ExceptionInfo:("abc" nil t)
  all-completions("abc" clojure\.lang\.ExceptionInfo: nil)
  completion-pcm--all-completions("" ("abc" point) clojure\.lang\.ExceptionInfo: nil)
  completion-basic-all-completions("abc" clojure\.lang\.ExceptionInfo: nil 3)
  #f(compiled-function (style) #<bytecode 0x1f03af9>)(basic)
  completion--some(#f(compiled-function (style) #<bytecode 0x1f03af9>) (basic partial-completion emacs22))
  completion--nth-completion(2 "abc" clojure\.lang\.ExceptionInfo: nil 3 (metadata))
  completion-all-completions("abc" clojure\.lang\.ExceptionInfo: nil 3 (metadata))
  company-capf--candidates("abc")
  company-capf(candidates "abc")
  apply(company-capf (candidates "abc"))
  company-call-backend-raw(candidates "abc")
  apply(company-call-backend-raw (candidates "abc"))
  company--force-sync(company-call-backend-raw (candidates "abc") company-capf)
  --> WRAPPED IN A CONDITION-CASE company-call-backend(candidates "abc")
  company-diag()
  funcall-interactively(company-diag)
  call-interactively(company-diag record nil)
  command-execute(company-diag record)
  counsel-M-x-action("company-diag")
  ivy-call()
  ivy-read("M-x " [dap-go-delve-path hasNextPage diary-included-files usages bmkp-file-this-dir-some-tags-jump-other-window dap-ui-breakpoint-log-message bmkp-tags-map csv-transpose gdb-script-syntax-propertize-function avy-words counsel-alias-expand magit-reflog-commit treemacs-project->path-status duplicate magit-wip-buffer-backed-up diredp-wrap-around-flag LOCALP woman-last-file-name none-but-delete js2-property-flag js2-visit-computed-prop-name-node sgml-syntax-propertize gdb-frame-locals-buffer local-only cl-print--preprocess \.frames clojure-docstring-fill-column dap-python--test-class-p HTMLTableSectionElement lsp:signature-help-active-signature\? js2-EXPORT js2-block-node-len cljr--cljc-file-p being omt one include-omitted-p org-duration-format epl-installed-packages \' :name-match bmkp-non-invokable-alist-only lsp--virtual-buffer-mappings js2-var-decl-node-pos--cmacro sessions magit-diff-wash-hunk we-thinkers-history-log define-mode-local-override lispy-bind-variable Move\ out\ of\ sexp ...] :predicate #f(compiled-function (sym) #<bytecode 0x1f1126d>) :require-match t :history counsel-M-x-history :action counsel-M-x-action :keymap (keymap (67108908 . counsel--info-lookup-symbol) (67108910 . counsel-find-symbol)) :initial-input nil :caller counsel-M-x)
  counsel-M-x()
  funcall-interactively(counsel-M-x)
  call-interactively(counsel-M-x nil nil)
  command-execute(counsel-M-x)

Emacs is entering the debugger despite the fact that the call to company-call-backend is wrapped in condition-case:

(condition-case nil
            (setq cc (company-call-backend 'candidates (company--prefix-str prefix))
                  annotations
                  (mapcar
                   (lambda (c) (cons c (company-call-backend 'annotation c)))
                   cc))
          (error (setq annotations 'error)))

Answer 1

Following from Drew's suggestion in the comments, we can see that company.el is using condition-case-unless-debug in a number of places, including in company-call-backend-raw -- which in your stack trace is being called after that "WRAPPED IN A CONDITION-CASE" company-call-backend call.

(condition-case-unless-debug VAR BODYFORM &rest HANDLERS)

Like ‘condition-case’ except that it does not prevent debugging.
More specifically if ‘debug-on-error’ is set then the debugger will be invoked
even if this catches the signal.