feat(format): case_collapse uses line_width via Doc-IR

pkg/format/dml.go

@@ -861,10 +861,6 @@ func alignSetItems(texts []string) []string {
 	return out
 }
 
-// caseCollapseWidth is the inline-length threshold under which case_collapse
-// keeps a CASE expression on one line even when case_when_wrap is set.
-const caseCollapseWidth = 60
-
 // dmlIsCaseStart reports whether t is a CASE keyword token.
 func dmlIsCaseStart(t cst.Tok) bool {
 	return t.Tok.Kind == lexer.Ident && lowerASCII(t.Tok.Text) == "case"
@@ -1001,10 +997,12 @@ func dmlFormatCase(toks []cst.Tok, st config.Style) string {
 	if !st.CaseWhenWrap {
 		return inline
 	}
-	if st.CaseCollapse && len(inline) <= caseCollapseWidth {
-		return inline
+	wrapped := dmlCaseWrapped(caseKw, operand, whens, elseKw, elseText, haveElse, endKw, st)
+	if st.CaseCollapse {
+		// Collapse when the one-line form fits in line_width.
+		return Render(Group(IfBreak(Text(wrapped), Text(inline))), st.LineWidth, st.Indent, st.Newline)
 	}
-	return dmlCaseWrapped(caseKw, operand, whens, elseKw, elseText, haveElse, endKw, st)
+	return wrapped
 }
 
 // dmlCaseInline renders a CASE expression on a single line.

pkg/format/dml_test.go

@@ -632,3 +632,18 @@ func TestWhereWhenLong(t *testing.T) {
 		t.Errorf("broken when_long should equal always:\n%s\n---\n%s", long, want)
 	}
 }
+
+func TestDMLCaseCollapseUsesLineWidth(t *testing.T) {
+	st := config.Default()
+	st.CaseWhenWrap = true
+	st.CaseCollapse = true
+	src := "select case when a = 1 then 'one' when a = 2 then 'two' else 'other' end from t;"
+	st.LineWidth = 120
+	if got := File(parser.Parse(src), st); strings.Contains(got, "\n  WHEN") {
+		t.Errorf("fits in 120, should collapse:\n%s", got)
+	}
+	st.LineWidth = 30
+	if got := File(parser.Parse(src), st); !strings.Contains(got, "\n  WHEN") {
+		t.Errorf("exceeds 30, should wrap:\n%s", got)
+	}
+}