Fix #4252 (Resolve multiple sensible indents) (#4285)

* Fix #4252

* Correct the test case

src/sqlfluff/utils/reflow/elements.py

@@ -203,6 +203,28 @@ class IndentStats:
     # Defaults to an empty tuple if unset.
     implicit_indents: Tuple[int, ...] = ()
 
+    @classmethod
+    def from_combination(cls, first: Optional["IndentStats"], second: "IndentStats"):
+        """Create IndentStats from two consecutive IndentStats.
+
+        This is mostly used for combining the effects of indent and dedent
+        tokens either side of a comment.
+
+        NOTE: The *first* is considered optional, because if we're
+        calling this function, we're assuming that there's always
+        a second.
+        """
+        # First check for the trivial case that we only have one.
+        if not first:
+            return second
+
+        # Otherwise, combine the two into one.
+        return cls(
+            first.impulse + second.impulse,
+            min(first.trough, first.impulse + second.trough),
+            second.implicit_indents,
+        )
+
 
 @dataclass(frozen=True)
 class ReflowPoint(ReflowElement):

src/sqlfluff/utils/reflow/reindent.py

@@ -476,8 +476,8 @@ def _crawl_indent_points(
     cached_indent_stats: Optional[IndentStats] = None
     for idx, elem in enumerate(elements):
         if isinstance(elem, ReflowPoint):
-            indent_stats = cached_indent_stats or elem.get_indent_impulse(
-                allow_implicit_indents
+            indent_stats = IndentStats.from_combination(
+                cached_indent_stats, elem.get_indent_impulse(allow_implicit_indents)
             )
             cached_indent_stats = None
 

test/fixtures/rules/std_rule_cases/L003.yml

@@ -1570,3 +1570,26 @@ test_fail_coverage_indent_trough:
         FROM foo
     )
     SELECT a FROM bar
+
+test_pass_combined_comment_impulses:
+  # This tests issue #4252
+  # https://github.com/sqlfluff/sqlfluff/issues/4252
+  pass_str: |
+    WITH cte AS (
+        SELECT *
+        FROM (
+            SELECT *
+            FROM table
+            WHERE
+                NOT bool_column AND NOT bool_column
+                AND some_column >= 1  -- This is a comment
+        )
+    ),
+
+    SELECT *
+    FROM cte
+    ;
+
+    SELECT *
+    FROM table3
+    ;