Fix: discard_(un)trimmed were always none in JSON report

This arose in commit 4fdeb12, where the
names of the classes DiscardUntrimmed and DiscardUntrimmed were changed to
IsTrimmed and IsUntrimmed because the name of the key in the JSON file is
(indirectly) derived from the class name.

Closes #824

CHANGES.rst

@@ -23,6 +23,8 @@ development version
   paired-end data.
 * :issue:`820`: Fix division by zero problem if ``--max-ee`` is used with an
   empty read. By @rhpvorderman.
+* :issue:`824`: Fix: discard_(un)trimmed values were always ``none`` in JSON
+  report.
 * Dropped support for Python 3.8.
 * Added support for Python 3.13.
 

src/cutadapt/predicates.py

@@ -152,6 +152,10 @@ def __repr__(self):
     def test(self, read, info: ModificationInfo):
         return not info.matches
 
+    @classmethod
+    def descriptive_identifier(cls) -> str:
+        return "discard_untrimmed"
+
 
 class IsTrimmed(Predicate):
     """
@@ -163,3 +167,7 @@ def __repr__(self):
 
     def test(self, read, info: ModificationInfo):
         return bool(info.matches)
+
+    @classmethod
+    def descriptive_identifier(cls) -> str:
+        return "discard_trimmed"

tests/test_commandline.py

@@ -1067,6 +1067,44 @@ def test_terminates_correctly_on_error_in_subprocess(tmp_path):
         main(params)
 
 
+def test_json_report_and_discard_untrimmed(tmp_path):
+    stats = main(
+        [
+            "--json",
+            str(tmp_path / "cutadapt.json"),
+            "--discard-untrimmed",
+            "-a",
+            "name=ACGT",
+            "-o",
+            str(tmp_path / "trimmed.fastq"),
+            datapath("illumina.fastq.gz"),
+        ]
+    )
+    assert stats.n == 100
+    assert stats.written == 64
+    js = stats.as_json()
+    assert js["read_counts"]["filtered"]["discard_untrimmed"] == 36
+
+
+def test_json_report_and_discard_trimmed(tmp_path):
+    stats = main(
+        [
+            "--json",
+            str(tmp_path / "cutadapt.json"),
+            "--discard-trimmed",
+            "-a",
+            "name=ACGT",
+            "-o",
+            str(tmp_path / "trimmed.fastq"),
+            datapath("illumina.fastq.gz"),
+        ]
+    )
+    assert stats.n == 100
+    assert stats.written == 36
+    js = stats.as_json()
+    assert js["read_counts"]["filtered"]["discard_trimmed"] == 64
+
+
 def test_json_report_with_demultiplexing_and_discard_untrimmed(tmp_path):
     stats = main(
         [
@@ -1082,6 +1120,8 @@ def test_json_report_with_demultiplexing_and_discard_untrimmed(tmp_path):
     )
     assert stats.n == 100
     assert stats.written == 64
+    js = stats.as_json()
+    assert js["read_counts"]["filtered"]["discard_untrimmed"] == 36
 
 
 @pytest.mark.timeout(1)