Added plain assignment

pkg/yqlib/doc/Assign Operator.md

@@ -1,4 +1,10 @@
-Updates the LHS using the expression on the RHS. Note that the RHS runs against the _original_ LHS value, so that you can evaluate a new value based on the old (e.g. increment).
+This operator is used to update node values. It can be used in either the:
+
+### plain form: `=`
+Which will assign the LHS node values to the RHS node values. The RHS expression is run against the matching nodes in the pipeline.
+
+### relative form: `|=`
+This will do a similar thing to the plain form, however, the RHS expression is run against _the LHS nodes_. This is useful for updating values based on old values, e.g. increment.
 ## Examples
 ### Update parent to be the child value
 Given a sample.yml file of:
@@ -17,6 +23,23 @@ a:
   g: foof
 ```
 
+### Update to be the sibling value
+Given a sample.yml file of:
+```yaml
+a:
+  b: child
+b: sibling
+```
+then
+```bash
+yq eval '.a = .b' sample.yml
+```
+will output
+```yaml
+a: sibling
+b: sibling
+```
+
 ### Updated multiple paths
 Given a sample.yml file of:
 ```yaml
@@ -36,6 +59,24 @@ c: potatoe
 ```
 
 ### Update string value
+Given a sample.yml file of:
+```yaml
+a:
+  b: apple
+```
+then
+```bash
+yq eval '.a.b = "frog"' sample.yml
+```
+will output
+```yaml
+a:
+  b: frog
+```
+
+### Update string value via |=
+Note there is no difference between `=` and `|=` when the RHS is a scalar
+
 Given a sample.yml file of:
 ```yaml
 a:

pkg/yqlib/doc/headers/Assign Operator.md

@@ -0,0 +1,7 @@
+This operator is used to update node values. It can be used in either the:
+
+### plain form: `=`
+Which will assign the LHS node values to the RHS node values. The RHS expression is run against the matching nodes in the pipeline.
+
+### relative form: `|=`
+This will do a similar thing to the plain form, however, the RHS expression is run against _the LHS nodes_. This is useful for updating values based on old values, e.g. increment.

pkg/yqlib/doc/headers/Update Assign Operator.md

@@ -1 +0,0 @@
-Updates the LHS using the expression on the RHS. Note that the RHS runs against the _original_ LHS value, so that you can evaluate a new value based on the old (e.g. increment).

pkg/yqlib/lib.go

@@ -37,8 +37,6 @@ var Union = &OperationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: U
 
 var Assign = &OperationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: AssignUpdateOperator}
 
-// TODO: implement this
-var PlainAssign = &OperationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: AssignUpdateOperator}
 var AssignAttributes = &OperationType{Type: "ASSIGN_ATTRIBUTES", NumArgs: 2, Precedence: 40, Handler: AssignAttributesOperator}
 var AssignStyle = &OperationType{Type: "ASSIGN_STYLE", NumArgs: 2, Precedence: 40, Handler: AssignStyleOperator}
 var AssignTag = &OperationType{Type: "ASSIGN_TAG", NumArgs: 2, Precedence: 40, Handler: AssignTagOperator}

pkg/yqlib/operator_assign.go

@@ -2,15 +2,28 @@ package yqlib
 
 import "container/list"
 
+type AssignOpPreferences struct {
+	UpdateAssign bool
+}
+
 func AssignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
 	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
 	if err != nil {
 		return nil, err
 	}
+	preferences := pathNode.Operation.Preferences.(*AssignOpPreferences)
+
+	var rhs *list.List
+	if !preferences.UpdateAssign {
+		rhs, err = d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	}
+
 	for el := lhs.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if preferences.UpdateAssign {
+			rhs, err = d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		}
 
 		if err != nil {
 			return nil, err

pkg/yqlib/operator_assign_test.go

@@ -13,6 +13,14 @@ var assignOperatorScenarios = []expressionScenario{
 			"D0, P[], (doc)::{a: {g: foof}}\n",
 		},
 	},
+	{
+		description: "Update to be the sibling value",
+		document:    `{a: {b: child}, b: sibling}`,
+		expression:  `.a = .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: sibling, b: sibling}\n",
+		},
+	},
 	{
 		description: "Updated multiple paths",
 		document:    `{a: fieldA, b: fieldB, c: fieldC}`,
@@ -24,6 +32,15 @@ var assignOperatorScenarios = []expressionScenario{
 	{
 		description: "Update string value",
 		document:    `{a: {b: apple}}`,
+		expression:  `.a.b = "frog"`,
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: frog}}\n",
+		},
+	},
+	{
+		description:    "Update string value via |=",
+		subdescription: "Note there is no difference between `=` and `|=` when the RHS is a scalar",
+		document:       `{a: {b: apple}}`,
 		expression:     `.a.b |= "frog"`,
 		expected: []string{
 			"D0, P[], (doc)::{a: {b: frog}}\n",
@@ -99,5 +116,5 @@ func TestAssignOperatorScenarios(t *testing.T) {
 	for _, tt := range assignOperatorScenarios {
 		testScenario(t, &tt)
 	}
-	documentScenarios(t, "Update Assign Operator", assignOperatorScenarios)
+	documentScenarios(t, "Assign Operator", assignOperatorScenarios)
 }

pkg/yqlib/operator_multilpy.go

@@ -112,6 +112,7 @@ func applyAssignment(d *dataTreeNavigator, pathIndexToStartFrom int, lhs *Candid
 	assignmentOp := &Operation{OperationType: AssignAttributes}
 	if rhs.Node.Kind == yaml.ScalarNode || rhs.Node.Kind == yaml.AliasNode {
 		assignmentOp.OperationType = Assign
+		assignmentOp.Preferences = &AssignOpPreferences{false}
 	}
 	rhsOp := &Operation{OperationType: ValueOp, CandidateNode: rhs}
 

pkg/yqlib/path_tokeniser.go

@@ -215,11 +215,11 @@ func initLexer() (*lex.Lexer, error) {
 	lexer.Add([]byte(`collect`), opToken(Collect))
 
 	lexer.Add([]byte(`\s*==\s*`), opToken(Equals))
-	lexer.Add([]byte(`\s*=\s*`), opToken(PlainAssign))
+	lexer.Add([]byte(`\s*=\s*`), opTokenWithPrefs(Assign, nil, &AssignOpPreferences{false}))
 
 	lexer.Add([]byte(`del`), opToken(DeleteChild))
 
-	lexer.Add([]byte(`\s*\|=\s*`), opToken(Assign))
+	lexer.Add([]byte(`\s*\|=\s*`), opTokenWithPrefs(Assign, nil, &AssignOpPreferences{true}))
 
 	lexer.Add([]byte(`\[-?[0-9]+\]`), arrayIndextoken(false))
 	lexer.Add([]byte(`\.\[-?[0-9]+\]`), arrayIndextoken(true))
@@ -303,7 +303,7 @@ func (p *pathTokeniser) Tokenise(path string) ([]*Token, error) {
 
 			if index != len(tokens)-1 && token.AssignOperation != nil &&
 				tokens[index+1].TokenType == OperationToken &&
-				tokens[index+1].Operation.OperationType == PlainAssign {
+				tokens[index+1].Operation.OperationType == Assign {
 				token.Operation = token.AssignOperation
 				skipNextToken = true
 			}