Improve ert-font-lock assertion parser (Bug#69714)

Fail on files with no assertions, parser now accepts multiple
carets per line and face lists:
* lisp/emacs-lisp/ert-font-lock.el: Assertion parser fix.
* test/lisp/emacs-lisp/ert-font-lock-resources/no-asserts.js:
* test/lisp/emacs-lisp/ert-font-lock-tests.el
(test-parse-comments--no-assertion-error)
(test-syntax-highlight-inline--caret-negated-wrong-face)
(test-macro-test--file-no-asserts): New test cases.
* doc/misc/ert.texi (Syntax Highlighting Tests): More syntax examples.

1 files changed, 40 insertions, 5 deletions

diff --git a/doc/misc/ert.texi b/doc/misc/ert.texi
index bd2ad495142..8767de71496 100644
--- a/doc/misc/ert.texi
+++ b/doc/misc/ert.texi
@@ -951,11 +951,13 @@ that assigns face properties to parts of the buffer.  The
 @code{ert-font-lock} package makes it possible to introduce unit tests
 checking face assignment.  Test assertions are included in code-level
 comments directly and can be read either from inline strings or files.
+The parser expects the input string to contain at least one assertion.
 
 Test assertion parser extracts tests from comment-only lines.  Every
-comment assertion line starts either with a caret (@samp{^}) or an
-arrow (@samp{<-}).  A caret/arrow should be followed immediately by the
-name of a face to be checked.
+comment assertion line starts either with a caret (@samp{^}) or an arrow
+(@samp{<-}).  A single caret/arrow or carets should be followed
+immediately by the name of a face or a list of faces to be checked
+against the @code{:face} property at point.
 
 The test then checks if the first non-assertion column above the caret
 contains a face expected by the assertion:
@@ -967,10 +969,43 @@ var variable = 11;
 //               ^ font-lock-punctuation-face
 // this is not an assertion, it's just a comment
 //   ^ font-lock-comment-face
+
+// multiple carets per line
+// ^^^^     ^    ^ font-lock-comment-face
+@end example
+
+Both symbol-only @code{:face} property values and assertion face values
+are normalized to single element lists so assertions below are
+equivalent:
+
+@example
+// single
+// ^ font-lock-comment-face
+// single
+// ^ (font-lock-comment-face)
+@end example
+
+Assertions can be negated:
+
+@example
+var variable = 11;
+//  ^ !font-lock-comment-face
+@end example
+
+It is possible to specify face lists in assertions:
+
+@example
+// TODO
+// ^^^^ (font-lock-comment-face hl-todo)
+     var test = 1;
+// ^    ()
+// ^    nil
+//   negation works as expected
+//   ^  !nil
 @end example
 
-The arrow means that the first non-empty column of the assertion line
-will be used for the check:
+The arrow (@samp{<-}) means that the first non-empty column of the
+assertion line will be used for the check:
 
 @example
 var variable = 1;