gopls/internal/codeaction: replace all occurrences of expression (ref…

…actor.extract.variable.all)

This change introduces a new refactoring code action
 "Extract n occurrences of expression".

The original "Extract Variable" is treated as a limited version
of "Extract n occurrences of expression", they share the same
underlying implementation. The difference is that
"extract_all" utilizes a slice of structural equal expression
by searching through the entire function body, while the limited
version simply append the expression under selection to that slice.

Also:
- change default variable name from "x" to "newVar",
default const name from "k" to "newConst",
users will almost always perform a rename after
extraction, so this change make it more discoverable,
especially when there are multiple matches.
- add marker test extract_expressions.txt and
extract_expressions_resolve.txt.

Updates golang/go#70085
Fixes golang/go#70563

Change-Id: I767b82be8a60d39c7aff087197c65d435b138826
GitHub-Last-Rev: b66a18d
GitHub-Pull-Request: #539
Reviewed-on: https://go-review.googlesource.com/c/tools/+/624035
Reviewed-by: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

gopls/doc/features/transformation.md

@@ -76,6 +76,7 @@ Gopls supports the following code actions:
 - [`refactor.extract.method`](#extract)
 - [`refactor.extract.toNewFile`](#extract.toNewFile)
 - [`refactor.extract.variable`](#extract)
+- [`refactor.extract.variable-all`](#extract)
 - [`refactor.inline.call`](#refactor.inline.call)
 - [`refactor.rewrite.changeQuote`](#refactor.rewrite.changeQuote)
 - [`refactor.rewrite.fillStruct`](#refactor.rewrite.fillStruct)
@@ -364,14 +365,22 @@ newly created declaration that contains the selected code:
   will be a method of the same receiver type.
 
 - **`refactor.extract.variable`** replaces an expression by a reference to a new
-  local variable named `x` initialized by the expression:
+  local variable named `newVar` initialized by the expression:
 
   ![Before extracting a var](../assets/extract-var-before.png)
   ![After extracting a var](../assets/extract-var-after.png)
 
 - **`refactor.extract.constant** does the same thing for a constant
   expression, introducing a local const declaration.
+- **`refactor.extract.variable-all`** replaces all occurrences of the selected expression
+within the function with a reference to a new local variable named `newVar`.
+This extracts the expression once and reuses it wherever it appears in the function.
 
+  ![Before extracting all occurrences of EXPR](../assets/extract-var-all-before.png)
+  ![After extracting all occurrences of EXPR](../assets/extract-var-all-after.png)
+
+  - **`refactor.extract.constant-all** does the same thing for a constant
+  expression, introducing a local const declaration.
 If the default name for the new declaration is already in use, gopls
 generates a fresh name.
 
@@ -387,10 +396,8 @@ number of cases where it falls short, including:
 
 - https://github.com/golang/go/issues/66289
 - https://github.com/golang/go/issues/65944
-- https://github.com/golang/go/issues/64821
 - https://github.com/golang/go/issues/63394
 - https://github.com/golang/go/issues/61496
-- https://github.com/golang/go/issues/50851
 
 The following Extract features are planned for 2024 but not yet supported:
 

gopls/doc/release/v0.18.0.md

@@ -28,10 +28,15 @@ func (C[T]) Pop() (T, bool) { ... }
 var _ Stack[int] = C[int]{}
 ```
 
+## Extract all occurrences of the same expression under selection
+
+When you have multiple instances of the same expression in a function,
+you can use this code action to extract it into a variable.
+All occurrences of the expression will be replaced with a reference to the new variable.
+
 ## Improvements to "Definition"
 
 The Definition query now supports additional locations:
 
 - When invoked on a return statement, it reports the location
   of the function's result variables.
-

gopls/internal/golang/codeaction.go

@@ -238,6 +238,8 @@ var codeActionProducers = [...]codeActionProducer{
 	{kind: settings.RefactorExtractToNewFile, fn: refactorExtractToNewFile},
 	{kind: settings.RefactorExtractConstant, fn: refactorExtractVariable, needPkg: true},
 	{kind: settings.RefactorExtractVariable, fn: refactorExtractVariable, needPkg: true},
+	{kind: settings.RefactorExtractConstantAll, fn: refactorExtractVariableAll, needPkg: true},
+	{kind: settings.RefactorExtractVariableAll, fn: refactorExtractVariableAll, needPkg: true},
 	{kind: settings.RefactorInlineCall, fn: refactorInlineCall, needPkg: true},
 	{kind: settings.RefactorRewriteChangeQuote, fn: refactorRewriteChangeQuote},
 	{kind: settings.RefactorRewriteFillStruct, fn: refactorRewriteFillStruct, needPkg: true},
@@ -467,14 +469,15 @@ func refactorExtractMethod(ctx context.Context, req *codeActionsRequest) error {
 // See [extractVariable] for command implementation.
 func refactorExtractVariable(ctx context.Context, req *codeActionsRequest) error {
 	info := req.pkg.TypesInfo()
-	if expr, _, err := canExtractVariable(info, req.pgf.File, req.start, req.end); err == nil {
+	if exprs, err := canExtractVariable(info, req.pgf.File, req.start, req.end, false); err == nil {
 		// Offer one of refactor.extract.{constant,variable}
 		// based on the constness of the expression; this is a
 		// limitation of the codeActionProducers mechanism.
 		// Beware that future evolutions of the refactorings
 		// may make them diverge to become non-complementary,
 		// for example because "if const x = ...; y {" is illegal.
-		constant := info.Types[expr].Value != nil
+		// Same as [refactorExtractVariableAll].
+		constant := info.Types[exprs[0]].Value != nil
 		if (req.kind == settings.RefactorExtractConstant) == constant {
 			title := "Extract variable"
 			if constant {
@@ -486,6 +489,35 @@ func refactorExtractVariable(ctx context.Context, req *codeActionsRequest) error
 	return nil
 }
 
+// refactorExtractVariableAll produces "Extract N occurrences of EXPR" code action.
+// See [extractAllOccursOfExpr] for command implementation.
+func refactorExtractVariableAll(ctx context.Context, req *codeActionsRequest) error {
+	info := req.pkg.TypesInfo()
+	// Don't suggest if only one expr is found,
+	// otherwise it will duplicate with [refactorExtractVariable]
+	if exprs, err := canExtractVariable(info, req.pgf.File, req.start, req.end, true); err == nil && len(exprs) > 1 {
+		start, end, err := req.pgf.NodeOffsets(exprs[0])
+		if err != nil {
+			return err
+		}
+		desc := string(req.pgf.Src[start:end])
+		if len(desc) >= 40 || strings.Contains(desc, "\n") {
+			desc = astutil.NodeDescription(exprs[0])
+		}
+		constant := info.Types[exprs[0]].Value != nil
+		if (req.kind == settings.RefactorExtractConstantAll) == constant {
+			var title string
+			if constant {
+				title = fmt.Sprintf("Extract %d occurrences of const expression: %s", len(exprs), desc)
+			} else {
+				title = fmt.Sprintf("Extract %d occurrences of %s", len(exprs), desc)
+			}
+			req.addApplyFixAction(title, fixExtractVariableAll, req.loc)
+		}
+	}
+	return nil
+}
+
 // refactorExtractToNewFile produces "Extract declarations to new file" code actions.
 // See [server.commandHandler.ExtractToNewFile] for command implementation.
 func refactorExtractToNewFile(ctx context.Context, req *codeActionsRequest) error {