feat(coverage): wire make coverage target + simplecov pipeline

Completes the coverage v1 pipeline by adding the Makefile target, the undercover driver script, the exclusion list, and the .gitignore entry. Uses simplecov JSON rather than LCOV as the collection format.

The LCOV vs simplecov choice: Undercover's :merge-report t option only supports simplecov. Since the pipeline runs tests per-file (matching test-unit's isolation pattern) and accumulates coverage across runs, merge-report is required. LCOV is better-supported by external coverage viewers, but for a primarily interactive workflow the on-disk format is an internal detail.

Other moves in this commit:

- Renamed cj/--coverage-parse-lcov to cj/--coverage-parse-simplecov and rewrote its tests for the JSON schema. Same signature, same semantics (file to set of covered lines), different parser.
- Renamed the backend protocol's :lcov-path key to :report-path, format-neutral and matching the renamed cj/--coverage-elisp-report-path function.
- The coverage target deletes modules/*.elc before running so undercover can instrument the .el sources. Without this, byte-compiled versions shadow the instrumentation and only a handful of pre-loaded modules end up with coverage data.
- Excluded tests/test-all-comp-errors.el from make coverage runs. That test byte-compiles every module, which fails under undercover's instrumentation. Excluded only from coverage. Normal make test still runs it.
- Updated docs/design/coverage.org to reflect the simplecov pivot with a historical note on why we moved off LCOV.

Verified end-to-end: make coverage produces .coverage/simplecov.json with 2717 of 4559 executable lines hit across 44 tracked modules.

1 files changed, 0 insertions, 149 deletions

diff --git a/tests/test-coverage-core--parse-lcov.el b/tests/test-coverage-core--parse-lcov.el
deleted file mode 100644
index a0a800ef..00000000
--- a/tests/test-coverage-core--parse-lcov.el
+++ /dev/null
@@ -1,149 +0,0 @@
-;;; test-coverage-core--parse-lcov.el --- Tests for cj/--coverage-parse-lcov -*- lexical-binding: t; -*-
-
-;;; Commentary:
-;; Unit tests for `cj/--coverage-parse-lcov', the pure helper that
-;; reads an LCOV file and returns a hash table of file → set of
-;; covered line numbers.
-;;
-;; LCOV format (the subset we care about):
-;;   SF:<source file>
-;;   DA:<line>,<hit count>
-;;   end_of_record
-;;
-;; A line counts as "covered" when its hit count is greater than zero.
-
-;;; Code:
-
-(require 'ert)
-
-(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
-(require 'coverage-core)
-
-(defun test-coverage-parse-lcov--write-temp-lcov (content)
-  "Write CONTENT to a temp file and return its path.
-Caller is responsible for deleting the file."
-  (let ((file (make-temp-file "test-lcov-" nil ".info")))
-    (with-temp-file file
-      (insert content))
-    file))
-
-;;; Normal cases
-
-(ert-deftest test-coverage-parse-lcov-single-file-all-covered ()
-  "Normal: one file with every line hit > 0 returns all lines in the set."
-  (let* ((content "SF:/path/to/foo.el\nDA:10,1\nDA:11,2\nDA:12,3\nend_of_record\n")
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let* ((result (cj/--coverage-parse-lcov file))
-               (lines (gethash "/path/to/foo.el" result)))
-          (should (hash-table-p result))
-          (should (= 3 (hash-table-count lines)))
-          (should (gethash 10 lines))
-          (should (gethash 11 lines))
-          (should (gethash 12 lines)))
-      (delete-file file))))
-
-(ert-deftest test-coverage-parse-lcov-multiple-files ()
-  "Normal: multiple file records in one LCOV file are both parsed."
-  (let* ((content (concat "SF:/a.el\nDA:1,1\nDA:2,1\nend_of_record\n"
-                          "SF:/b.el\nDA:5,1\nend_of_record\n"))
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let ((result (cj/--coverage-parse-lcov file)))
-          (should (= 2 (hash-table-count result)))
-          (should (gethash "/a.el" result))
-          (should (gethash "/b.el" result)))
-      (delete-file file))))
-
-(ert-deftest test-coverage-parse-lcov-mixed-hits ()
-  "Normal: lines with hit count 0 are excluded; positive counts included."
-  (let* ((content "SF:/foo.el\nDA:1,0\nDA:2,1\nDA:3,0\nDA:4,5\nend_of_record\n")
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let* ((result (cj/--coverage-parse-lcov file))
-               (lines (gethash "/foo.el" result)))
-          (should (= 2 (hash-table-count lines)))
-          (should-not (gethash 1 lines))
-          (should (gethash 2 lines))
-          (should-not (gethash 3 lines))
-          (should (gethash 4 lines)))
-      (delete-file file))))
-
-;;; Boundary cases
-
-(ert-deftest test-coverage-parse-lcov-empty-file ()
-  "Boundary: empty LCOV file returns an empty hash table, not nil."
-  (let ((file (test-coverage-parse-lcov--write-temp-lcov "")))
-    (unwind-protect
-        (let ((result (cj/--coverage-parse-lcov file)))
-          (should (hash-table-p result))
-          (should (= 0 (hash-table-count result))))
-      (delete-file file))))
-
-(ert-deftest test-coverage-parse-lcov-file-with-spaces-in-path ()
-  "Boundary: filename with spaces is parsed as one key."
-  (let* ((content "SF:/my path/with spaces.el\nDA:1,1\nend_of_record\n")
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let ((result (cj/--coverage-parse-lcov file)))
-          (should (gethash "/my path/with spaces.el" result)))
-      (delete-file file))))
-
-(ert-deftest test-coverage-parse-lcov-extra-lcov-fields-ignored ()
-  "Boundary: LF/LH/BRDA/FN fields don't break parsing; only DA matters."
-  (let* ((content (concat "SF:/foo.el\n"
-                          "FN:10,some-function\n"
-                          "FNDA:1,some-function\n"
-                          "DA:10,1\n"
-                          "DA:11,1\n"
-                          "LF:2\n"
-                          "LH:2\n"
-                          "BRDA:10,0,0,1\n"
-                          "end_of_record\n"))
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let* ((result (cj/--coverage-parse-lcov file))
-               (lines (gethash "/foo.el" result)))
-          (should (= 2 (hash-table-count lines)))
-          (should (gethash 10 lines))
-          (should (gethash 11 lines)))
-      (delete-file file))))
-
-(ert-deftest test-coverage-parse-lcov-all-zero-hits ()
-  "Boundary: file with no covered lines returns an empty set for that file."
-  (let* ((content "SF:/foo.el\nDA:1,0\nDA:2,0\nend_of_record\n")
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let* ((result (cj/--coverage-parse-lcov file))
-               (lines (gethash "/foo.el" result)))
-          (should (hash-table-p lines))
-          (should (= 0 (hash-table-count lines))))
-      (delete-file file))))
-
-;;; Error cases
-
-(ert-deftest test-coverage-parse-lcov-missing-file-errors ()
-  "Error: nonexistent file signals a user-error naming the path."
-  (should-error (cj/--coverage-parse-lcov "/nonexistent/path/xyz.info")
-                :type 'user-error))
-
-(ert-deftest test-coverage-parse-lcov-malformed-da-line-skipped ()
-  "Error: malformed DA lines are skipped; parsing continues on the rest."
-  (let* ((content (concat "SF:/foo.el\n"
-                          "DA:not-a-number,1\n"
-                          "DA:10,1\n"
-                          "DA:\n"
-                          "DA:11,notanumber\n"
-                          "DA:12,2\n"
-                          "end_of_record\n"))
-         (file (test-coverage-parse-lcov--write-temp-lcov content)))
-    (unwind-protect
-        (let* ((result (cj/--coverage-parse-lcov file))
-               (lines (gethash "/foo.el" result)))
-          (should (= 2 (hash-table-count lines)))
-          (should (gethash 10 lines))
-          (should (gethash 12 lines)))
-      (delete-file file))))
-
-(provide 'test-coverage-core--parse-lcov)
-;;; test-coverage-core--parse-lcov.el ends here