Avoid certain cases where 'is' is in its own line

extensions/default_unparsing_config.json

@@ -5309,17 +5309,88 @@
               {
                 "kind": "recurse_field",
                 "field": "f_aspects"
-              },
-              "line",
-              {
-                "kind": "text",
-                "text": "is"
               }
-            ]
+            ],
+            "id": "subp_spec"
           },
           {
-            "kind": "recurse_field",
-            "field": "f_decls"
+            "kind": "ifKind",
+            "field": "f_aspects",
+            "default": {
+              "kind": "ifBreak",
+              "groupId": "subp_spec",
+              "flatContents": {
+                "kind": "group",
+                "document": [
+                  {
+                    "kind": "group",
+                    "document": [
+                      "line",
+                      {
+                        "kind": "text",
+                        "text": "is"
+                      }
+                    ]
+                  },
+                  {
+                    "kind": "recurse_field",
+                    "field": "f_decls"
+                  }
+                ]
+              },
+              "breakContents": {
+                "kind": "group",
+                "document": [
+                  "hardline",
+                  {
+                    "kind": "text",
+                    "text": "is"
+                  },
+                  {
+                    "kind": "recurse_field",
+                    "field": "f_decls"
+                  }
+                ]
+              }
+            },
+            "null": {
+              "kind": "ifBreak",
+              "groupId": "subp_spec",
+              "flatContents": {
+                "kind": "group",
+                "document": [
+                  {
+                    "kind": "group",
+                    "document": [
+                      "line",
+                      {
+                        "kind": "text",
+                        "text": "is"
+                      }
+                    ]
+                  },
+                  {
+                    "kind": "recurse_field",
+                    "field": "f_decls"
+                  }
+                ]
+              },
+              "breakContents": {
+                "kind": "group",
+                "document": [
+                  "line",
+                  {
+                    "kind": "text",
+                    "text": "is"
+                  },
+                  {
+                    "kind": "recurse_field",
+                    "field": "f_decls"
+                  }
+                ]
+              }
+            },
+            "matchers": []
           },
           {
             "kind": "text",

testsuite/tests/unparsing/subp_body/long_subp_spec_no_decls/input.ada

@@ -0,0 +1,10 @@
+function To_Source_Location_Range
+  (Self : Langkit_Text_Document'Class; A_Range : LSP.Structures.A_Range)
+   return Langkit_Support.Slocs.Source_Location_Range
+is
+begin
+   return
+     Langkit_Support.Slocs.Make_Range
+       (Self.To_Source_Location (A_Range.start),
+        Self.To_Source_Location (A_Range.an_end));
+end To_Source_Location_Range;

testsuite/tests/unparsing/subp_body/long_subp_spec_no_decls/test.out

@@ -0,0 +1,9 @@
+function To_Source_Location_Range
+  (Self : Langkit_Text_Document'Class; A_Range : LSP.Structures.A_Range)
+   return Langkit_Support.Slocs.Source_Location_Range is
+begin
+   return
+     Langkit_Support.Slocs.Make_Range
+       (Self.To_Source_Location (A_Range.start),
+        Self.To_Source_Location (A_Range.an_end));
+end To_Source_Location_Range;

testsuite/tests/unparsing/subp_body/long_subp_spec_no_decls/test.yaml

@@ -0,0 +1,6 @@
+driver: unparser
+rule: subp_body
+description: |
+  For a `SubpBody` node whose `f_decls` is empty, null `f_aspects` and
+  `f_subp_spec` breaks, test that the `is` is added to the end of
+  `f_subp_spec` if it fits.

testsuite/tests/unparsing/subp_body/long_subp_spec_with_decls/input.ada

@@ -0,0 +1,10 @@
+function To_Source_Location_Range
+  (Self : Langkit_Text_Document'Class; A_Range : LSP.Structures.A_Range)
+   return Langkit_Support.Slocs.Source_Location_Range is
+   I : Integer;
+begin
+   return
+     Langkit_Support.Slocs.Make_Range
+       (Self.To_Source_Location (A_Range.start),
+        Self.To_Source_Location (A_Range.an_end));
+end To_Source_Location_Range;

testsuite/tests/unparsing/subp_body/long_subp_spec_with_decls/test.out

@@ -0,0 +1,11 @@
+function To_Source_Location_Range
+  (Self : Langkit_Text_Document'Class; A_Range : LSP.Structures.A_Range)
+   return Langkit_Support.Slocs.Source_Location_Range
+is
+   I : Integer;
+begin
+   return
+     Langkit_Support.Slocs.Make_Range
+       (Self.To_Source_Location (A_Range.start),
+        Self.To_Source_Location (A_Range.an_end));
+end To_Source_Location_Range;

testsuite/tests/unparsing/subp_body/long_subp_spec_with_decls/test.yaml

@@ -0,0 +1,5 @@
+driver: unparser
+rule: subp_body
+description: |
+  For a `SubpBody` node whose `f_decls` is not empty, null `f_aspects` and
+  `f_subp_spec` breaks, test that a line break is added before the `is`.