Add config migration of paging section to pagers array

pkg/config/app_config.go

@@ -310,6 +310,11 @@ func computeMigratedConfig(path string, content []byte, changes *ChangesSet) ([]
 		return nil, false, fmt.Errorf("Couldn't migrate config file at `%s`: %w", path, err)
 	}
 
+	err = migratePagers(&rootNode, changes)
+	if err != nil {
+		return nil, false, fmt.Errorf("Couldn't migrate config file at `%s`: %w", path, err)
+	}
+
 	// Add more migrations here...
 
 	if reflect.DeepEqual(rootNode, originalCopy) {
@@ -469,6 +474,37 @@ func migrateAllBranchesLogCmd(rootNode *yaml.Node, changes *ChangesSet) error {
 	})
 }
 
+func migratePagers(rootNode *yaml.Node, changes *ChangesSet) error {
+	return yaml_utils.TransformNode(rootNode, []string{"git"}, func(gitNode *yaml.Node) error {
+		pagingKeyNode, pagingValueNode := yaml_utils.LookupKey(gitNode, "paging")
+		if pagingKeyNode == nil || pagingValueNode.Kind != yaml.MappingNode {
+			// If there's no "paging" section (or it's not an object), there's nothing to do
+			return nil
+		}
+
+		pagersKeyNode, _ := yaml_utils.LookupKey(gitNode, "pagers")
+		if pagersKeyNode != nil {
+			// Conversely, if there *is* already a "pagers" array, we also have nothing to do.
+			// This covers the case where the user keeps both the "paging" section and the "pagers"
+			// array for the sake of easier testing of old versions.
+			return nil
+		}
+
+		pagingKeyNode.Value = "pagers"
+		pagingContentCopy := pagingValueNode.Content
+		pagingValueNode.Kind = yaml.SequenceNode
+		pagingValueNode.Tag = "!!seq"
+		pagingValueNode.Content = []*yaml.Node{{
+			Kind:    yaml.MappingNode,
+			Content: pagingContentCopy,
+		}}
+
+		changes.Add("Moved git.paging object to git.pagers array")
+
+		return nil
+	})
+}
+
 func (c *AppConfig) GetDebug() bool {
 	return c.debug
 }

pkg/config/app_config_test.go

@@ -1089,3 +1089,98 @@ func TestAllBranchesLogCmdMigrations(t *testing.T) {
 		})
 	}
 }
+
+func TestPagerMigration(t *testing.T) {
+	scenarios := []struct {
+		name              string
+		input             string
+		expected          string
+		expectedDidChange bool
+		expectedChanges   []string
+	}{
+		{
+			name:              "Incomplete Configuration Passes uneventfully",
+			input:             "git:",
+			expectedDidChange: false,
+			expectedChanges:   []string{},
+		},
+		{
+			name: "No paging section",
+			input: `git:
+  autoFetch: true
+`,
+			expected: `git:
+  autoFetch: true
+`,
+			expectedDidChange: false,
+			expectedChanges:   []string{},
+		},
+		{
+			name: "Both paging and pagers exist",
+			input: `git:
+  paging:
+    pager: delta --dark --paging=never
+  pagers:
+    - diff: diff-so-fancy
+`,
+			expected: `git:
+  paging:
+    pager: delta --dark --paging=never
+  pagers:
+    - diff: diff-so-fancy
+`,
+			expectedDidChange: false,
+			expectedChanges:   []string{},
+		},
+		{
+			name: "paging is not an object",
+			input: `git:
+  paging: 5
+`,
+			expected: `git:
+  paging: 5
+`,
+			expectedDidChange: false,
+			expectedChanges:   []string{},
+		},
+		{
+			name: "paging is moved to pagers array (keeping the order)",
+			input: `git:
+  paging:
+    pager: delta --dark --paging=never
+  autoFetch: true
+`,
+			expected: `git:
+  pagers:
+    - pager: delta --dark --paging=never
+  autoFetch: true
+`,
+			expectedDidChange: true,
+			expectedChanges:   []string{"Moved git.paging object to git.pagers array"},
+		},
+		{
+			name: "paging is moved to pagers array even if empty",
+			input: `git:
+  paging: {}
+`,
+			expected: `git:
+  pagers: [{}]
+`,
+			expectedDidChange: true,
+			expectedChanges:   []string{"Moved git.paging object to git.pagers array"},
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			changes := NewChangesSet()
+			actual, didChange, err := computeMigratedConfig("path doesn't matter", []byte(s.input), changes)
+			assert.NoError(t, err)
+			assert.Equal(t, s.expectedDidChange, didChange)
+			if didChange {
+				assert.Equal(t, s.expected, string(actual))
+			}
+			assert.Equal(t, s.expectedChanges, changes.ToSliceFromOldest())
+		})
+	}
+}