From 94052731d0f955ad8c9ec9fb9392470f48187d3f Mon Sep 17 00:00:00 2001
From: Oliver Sanders <oliver.sanders@metoffice.gov.uk>
Date: Tue, 17 Sep 2024 15:11:45 +0100
Subject: [PATCH] cylc_lang: permit preprocessing in intercycle offsets

---
 cylc/sphinx_ext/cylc_lang/__init__.py |  8 ++++++++
 cylc/sphinx_ext/cylc_lang/lexers.py   | 26 ++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/cylc/sphinx_ext/cylc_lang/__init__.py b/cylc/sphinx_ext/cylc_lang/__init__.py
index 3aa78b9..82ef51d 100644
--- a/cylc/sphinx_ext/cylc_lang/__init__.py
+++ b/cylc/sphinx_ext/cylc_lang/__init__.py
@@ -30,12 +30,20 @@
 
    .. code-block:: cylc
 
+      # Jinja2
+
+      {% set final_cycle_point = final_cycle_point | default('') %}
+      {% set duration = duration | default('P1Y') %}
+
       [scheduling]
           initial cycle point = 2000
+          final cycle point = {{ final_cycle_point }}
           [[graph]]
               P1Y = """
                   @wall_clock => foo? => bar
                   (foo? & bar) => pub
+
+                  foo[-{{ duration }}+P1D] => foo
               """
 
 .. note::
diff --git a/cylc/sphinx_ext/cylc_lang/lexers.py b/cylc/sphinx_ext/cylc_lang/lexers.py
index cefb44c..7836263 100644
--- a/cylc/sphinx_ext/cylc_lang/lexers.py
+++ b/cylc/sphinx_ext/cylc_lang/lexers.py
@@ -200,9 +200,35 @@ class CylcLexer(RegexLexer):
             include('integer-duration'),  # matches a subset of iso8601
             include('iso8601-duration'),
             (r'[\^\$]', INTERCYCLE_OFFSET_TOKEN),
+            (
+                # anything that contains Jinja2 syntax
+                r'(?=[^\]]*{{)',
+                INTERCYCLE_OFFSET_TOKEN,
+                'preproc-intercycle-offset',
+            ),
+            (
+                # anything that contains EmPy syntax
+                r'(?=[^\]]*@)',
+                INTERCYCLE_OFFSET_TOKEN,
+                'preproc-intercycle-offset',
+            ),
             (r'\]', Text, '#pop')
         ],
 
+        # Task inter-cycle offset with preprocessing: foo[-{{duration}}+P1D]
+        # Note: This is done in its own section so that we don't bypass the
+        # validation that has been implemented for explicit offsets
+        'preproc-intercycle-offset': [
+            # permit pre-processing
+            include('preproc'),
+            # interpret all other text as part of the offset
+            # (we can't perform validation when preprocessing is involved)
+            (r'[^\]]', INTERCYCLE_OFFSET_TOKEN),
+            # the first "]" (outside of preprocessing) marks the end of the
+            # offset
+            (r'(?=\])', Text, '#pop')
+        ],
+
         # generic Cylc cycle point:  2000
         'cycle-point': [
             # validating the cycle point as a regex [effectively] requires