From a1f8d7cd8fc52af3baf0bac62e4a564591782acf Mon Sep 17 00:00:00 2001
From: Nicholas Long <nicholas.long@nrel.gov>
Date: Tue, 14 Jul 2026 06:11:59 -0600
Subject: [PATCH] support triple braces in mot files

---
 CHANGELOG.md                     |  6 +++++
 internal/format/template.go      | 40 ++++++++++++++++++++++----------
 internal/format/template_test.go | 22 ++++++++++++++++++
 3 files changed, 56 insertions(+), 12 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f9df301..02d2d5e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Unreleased
 
+* Fix `.mot`/`.mopt` formatting collapsing the space in a single-element array
+  literal whose element is a Jinja expression (e.g. `{ {{ data[...] }} }`),
+  which produced an ambiguous `{{{ ... }}}` triple-brace sequence. A single
+  disambiguating space is now preserved whenever a restored Jinja expression's
+  own `{{`/`}}` delimiters would otherwise merge with an adjacent Modelica
+  array brace.
 * Tweak default formatting for readability (issue #26):
   * Keep a function call with a single argument on one line instead of breaking
     the argument onto its own line, e.g. `pre(x)`, `der(y)`, `sin(z)`,
diff --git a/internal/format/template.go b/internal/format/template.go
index 34fb45f..1b6e67f 100644
--- a/internal/format/template.go
+++ b/internal/format/template.go
@@ -324,21 +324,37 @@ func reverseSub(text string, sub *subMap) (string, error) {
 	text = blockCommentedSubRegex.ReplaceAllString(text, "${1}")
 	text = trimWhitespaceBeforeRawPunctuation(text, sub)
 
-	var firstErr error
-	restored := normalSubRegex.ReplaceAllStringFunc(text, func(match string) string {
-		orig, err := sub.getText(match)
+	matches := normalSubRegex.FindAllStringIndex(text, -1)
+	var b strings.Builder
+	last := 0
+	for _, m := range matches {
+		start, end := m[0], m[1]
+		orig, err := sub.getText(text[start:end])
 		if err != nil {
-			if firstErr == nil {
-				firstErr = err
-			}
-			return match
+			return "", err
 		}
-		return orig
-	})
-	if firstErr != nil {
-		return "", firstErr
+
+		b.WriteString(text[last:start])
+
+		// A restored Jinja expression that starts/ends with its own `{{`/`}}`
+		// delimiters can collide with an immediately adjacent Modelica array
+		// brace (e.g. `{{{ ... }}}`), which is ambiguous when the template is
+		// re-rendered. Insert a single disambiguating space in that case. Only
+		// `{{`/`}}` expression delimiters are checked (not `{%`/`%}` control
+		// tags such as `{% raw %}`) so control-statement placeholders are
+		// unaffected.
+		if start > 0 && text[start-1] == '{' && strings.HasPrefix(orig, "{{") {
+			b.WriteByte(' ')
+		}
+		b.WriteString(orig)
+		if end < len(text) && text[end] == '}' && strings.HasSuffix(orig, "}}") {
+			b.WriteByte(' ')
+		}
+
+		last = end
 	}
-	return restored, nil
+	b.WriteString(text[last:])
+	return b.String(), nil
 }
 
 func trimWhitespaceBeforeRawPunctuation(text string, sub *subMap) string {
diff --git a/internal/format/template_test.go b/internal/format/template_test.go
index b8c27a2..5daedd0 100644
--- a/internal/format/template_test.go
+++ b/internal/format/template_test.go
@@ -292,6 +292,28 @@ end LoopedArray;
 	a.Contains(formatted, "{% for building in data[\"building_load_files\"] %}")
 }
 
+// TestSingleElementArrayExpressionKeepsDisambiguatingSpace guards against the
+// formatter collapsing `{ {{ expr }} }` into `{{{ expr }}}`. The Modelica
+// array formatter normally strips the space inside a single-element array
+// literal, but doing so here would make the restored Jinja expression's own
+// `{{`/`}}` delimiters collide with the surrounding array braces, producing
+// an ambiguous triple-brace sequence when the template is later rendered.
+func TestSingleElementArrayExpressionKeepsDisambiguatingSpace(t *testing.T) {
+	a := require.New(t)
+	original := `model NominalArray
+  parameter Real a[3] = fill({ {{ data["nominal_values"]["boiler_efficiency"] }} });
+end NominalArray;
+`
+	var out bytes.Buffer
+	err := processTemplate(original, &out, Config{-1, false, false, false}, DialectJinja, "nominal-array.mot")
+	a.NoError(err)
+
+	formatted := out.String()
+	a.NotContains(formatted, `{{{`, "restored Jinja expression must not merge with a literal Modelica array brace")
+	a.NotContains(formatted, `}}}`, "restored Jinja expression must not merge with a literal Modelica array brace")
+	a.Contains(formatted, `{ {{ data["nominal_values"]["boiler_efficiency"] }} }`)
+}
+
 func TestInlineExpressionBeforeRawPunctuationDoesNotGainRenderedSpace(t *testing.T) {
 	a := require.New(t)
 	original := `model PumpTemplate