back.rtlil: espace { and } in format string

Fixes #1518

Author: rroohhh

amaranth/back/rtlil.py

@@ -1132,7 +1132,7 @@ def emit_print(self, cell_idx, cell):
         if cell.format is not None:
             for chunk in cell.format.chunks:
                 if isinstance(chunk, str):
-                    format.append(chunk)
+                    format.append(chunk.replace("{", "{{").replace("}", "}}"))
                 else:
                     spec = _ast.Format._parse_format_spec(chunk.format_desc, _ast.Shape(len(chunk.value), chunk.signed))
                     type = spec["type"]

tests/test_back_rtlil.py

@@ -2008,6 +2008,51 @@ def test_print_align(self):
         end
         """)
 
+    def test_escape_curly(self):
+        m = Module()
+        m.d.comb += [
+            Print("{"),
+            Print("}"),
+        ]
+        self.assertRTLIL(m, [], R"""
+        attribute \generator "Amaranth"
+        attribute \top 1
+        module \top
+            wire width 1 $1
+            wire width 1 $2
+            process $3
+                assign $1 [0] 1'0
+                assign $1 [0] 1'1
+            end
+            cell $print $4
+                parameter \FORMAT "{{\n"
+                parameter \ARGS_WIDTH 0
+                parameter signed \PRIORITY 32'11111111111111111111111111111110
+                parameter \TRG_ENABLE 0
+                parameter \TRG_WIDTH 0
+                parameter \TRG_POLARITY 0
+                connect \EN $1 [0]
+                connect \ARGS { }
+                connect \TRG { }
+            end
+            process $5
+                assign $2 [0] 1'0
+                assign $2 [0] 1'1
+            end
+            cell $print $6
+                parameter \FORMAT "}}\n"
+                parameter \ARGS_WIDTH 0
+                parameter signed \PRIORITY 32'11111111111111111111111111111100
+                parameter \TRG_ENABLE 0
+                parameter \TRG_WIDTH 0
+                parameter \TRG_POLARITY 0
+                connect \EN $2 [0]
+                connect \ARGS { }
+                connect \TRG { }
+            end
+        end
+        """)
+
 
 class DetailTestCase(RTLILTestCase):
     def test_enum(self):