x/tools/gopls: implement struct field generation quickfix

gopls/doc/features/diagnostics.md

@@ -272,6 +272,35 @@ func doSomething(i int) string {
   panic("unimplemented")
 }
 ```
+
+### `StubMissingStructField`: Declare missing field T.f
+
+When you attempt to access a field on a type that does not have the field,
+the compiler will report an error such as "type X has no field or method Y".
+In this scenario, gopls now offers a quick fix to generate a stub declaration of
+the missing field, inferring its type from the accessing type or assigning a designated value.
+
+Consider the following code where `Foo` does not have a field `bar`:
+
+```go
+type Foo struct{}
+
+func main() {
+  var s string
+  f := Foo{}
+  s = f.bar // error: f.bar undefined (type Foo has no field or method bar)
+}
+```
+
+Gopls will offer a quick fix, "Declare missing field Foo.bar".
+When invoked, it creates the following declaration:
+
+```go
+type Foo struct{
+  bar string
+}
+```
+
 <!--
 
 dorky details and deletia:

gopls/doc/release/v0.17.0.md

@@ -196,3 +196,24 @@ causing `Add` to race with `Wait`.
 (This check is equivalent to
 [staticcheck's SA2000](https://staticcheck.dev/docs/checks#SA2000),
 but is enabled by default.)
+
+## Add test for function or method
+
+If the selected chunk of code is part of a function or method declaration F,
+gopls will offer the "Add test for F" code action, which adds a new test for the
+selected function in the corresponding `_test.go` file. The generated test takes
+into account its signature, including input parameters and results.
+
+Since this feature is implemented by the server (gopls), it is compatible with
+all LSP-compliant editors. VS Code users may continue to use the client-side
+`Go: Generate Unit Tests For file/function/package` command which utilizes the
+[gotests](https://github.com/cweill/gotests) tool.
+
+## Generate missing struct field from access
+
+When you attempt to access a field on a type that does not have the field,
+the compiler will report an error like “type X has no field or method Y”.
+Gopls now offers a new code action, “Declare missing field of T.f”,
+where T is the concrete type and f is the undefined field.
+The stub field's signature is inferred
+from the context of the access.

gopls/internal/golang/codeaction.go

@@ -41,7 +41,6 @@ import (
 //
 // See ../protocol/codeactionkind.go for some code action theory.
 func CodeActions(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle, rng protocol.Range, diagnostics []protocol.Diagnostic, enabled func(protocol.CodeActionKind) bool, trigger protocol.CodeActionTriggerKind) (actions []protocol.CodeAction, _ error) {
-
 	loc := protocol.Location{URI: fh.URI(), Range: rng}
 
 	pgf, err := snapshot.ParseGo(ctx, fh, parsego.Full)
@@ -328,14 +327,23 @@ func quickFix(ctx context.Context, req *codeActionsRequest) error {
 			}
 
 		// "type X has no field or method Y" compiler error.
-		// Offer a "Declare missing method T.f" code action.
-		// See [stubMissingCalledFunctionFixer] for command implementation.
 		case strings.Contains(msg, "has no field or method"):
 			path, _ := astutil.PathEnclosingInterval(req.pgf.File, start, end)
+
+			// Offer a "Declare missing method T.f" code action if a CallStubInfo found.
+			// See [stubMissingCalledFunctionFixer] for command implementation.
 			si := stubmethods.GetCallStubInfo(req.pkg.FileSet(), info, path, start)
 			if si != nil {
 				msg := fmt.Sprintf("Declare missing method %s.%s", si.Receiver.Obj().Name(), si.MethodName)
 				req.addApplyFixAction(msg, fixMissingCalledFunction, req.loc)
+			} else {
+				// Offer a "Declare missing field T.f" code action.
+				// See [stubMissingStructFieldFixer] for command implementation.
+				fi := stubmethods.GetFieldStubInfo(req.pkg.FileSet(), info, path)
+				if fi != nil {
+					msg := fmt.Sprintf("Declare missing struct field %s.%s", fi.Named.Obj().Name(), fi.Expr.Sel.Name)
+					req.addApplyFixAction(msg, fixMissingStructField, req.loc)
+				}
 			}
 
 		// "undeclared name: X" or "undefined: X" compiler error.

gopls/internal/golang/fix.go

@@ -69,6 +69,7 @@ const (
 	fixCreateUndeclared        = "create_undeclared"
 	fixMissingInterfaceMethods = "stub_missing_interface_method"
 	fixMissingCalledFunction   = "stub_missing_called_function"
+	fixMissingStructField      = "stub_missing_struct_field"
 )
 
 // ApplyFix applies the specified kind of suggested fix to the given
@@ -115,6 +116,7 @@ func ApplyFix(ctx context.Context, fix string, snapshot *cache.Snapshot, fh file
 		fixCreateUndeclared:        singleFile(createUndeclared),
 		fixMissingInterfaceMethods: stubMissingInterfaceMethodsFixer,
 		fixMissingCalledFunction:   stubMissingCalledFunctionFixer,
+		fixMissingStructField:      stubMissingStructFieldFixer,
 	}
 	fixer, ok := fixers[fix]
 	if !ok {

gopls/internal/golang/stub.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"go/ast"
 	"go/format"
 	"go/parser"
 	"go/token"
@@ -51,6 +52,18 @@ func stubMissingCalledFunctionFixer(ctx context.Context, snapshot *cache.Snapsho
 	return insertDeclsAfter(ctx, snapshot, pkg.Metadata(), si.Fset, si.After, si.Emit)
 }
 
+// stubMissingStructFieldFixer returns a suggested fix to declare the missing
+// field that the user may want to generate based on SelectorExpr
+// at the cursor position.
+func stubMissingStructFieldFixer(ctx context.Context, snapshot *cache.Snapshot, pkg *cache.Package, pgf *parsego.File, start, end token.Pos) (*token.FileSet, *analysis.SuggestedFix, error) {
+	nodes, _ := astutil.PathEnclosingInterval(pgf.File, start, end)
+	fi := stubmethods.GetFieldStubInfo(pkg.FileSet(), pkg.TypesInfo(), nodes)
+	if fi == nil {
+		return nil, nil, fmt.Errorf("invalid type request")
+	}
+	return insertStructField(ctx, snapshot, pkg.Metadata(), fi)
+}
+
 // An emitter writes new top-level declarations into an existing
 // file. References to symbols should be qualified using qual, which
 // respects the local import environment.
@@ -83,76 +96,10 @@ func insertDeclsAfter(ctx context.Context, snapshot *cache.Snapshot, mp *metadat
 		return nil, nil, bug.Errorf("can't find metadata for file %s among dependencies of %s", declPGF.URI, mp)
 	}
 
-	// Build import environment for the declaring file.
-	// (typesinternal.FileQualifier works only for complete
-	// import mappings, and requires types.)
-	importEnv := make(map[ImportPath]string) // value is local name
-	for _, imp := range declPGF.File.Imports {
-		importPath := metadata.UnquoteImportPath(imp)
-		var name string
-		if imp.Name != nil {
-			name = imp.Name.Name
-			if name == "_" {
-				continue
-			} else if name == "." {
-				name = "" // see types.Qualifier
-			}
-		} else {
-			// Use the correct name from the metadata of the imported
-			// package---not a guess based on the import path.
-			mp := snapshot.Metadata(declMeta.DepsByImpPath[importPath])
-			if mp == nil {
-				continue // can't happen?
-			}
-			name = string(mp.Name)
-		}
-		importEnv[importPath] = name // latest alias wins
-	}
-
-	// Create a package name qualifier that uses the
-	// locally appropriate imported package name.
-	// It records any needed new imports.
-	// TODO(adonovan): factor with golang.FormatVarType?
-	//
-	// Prior to CL 469155 this logic preserved any renaming
-	// imports from the file that declares the interface
-	// method--ostensibly the preferred name for imports of
-	// frequently renamed packages such as protobufs.
-	// Now we use the package's declared name. If this turns out
-	// to be a mistake, then use parseHeader(si.iface.Pos()).
-	//
-	type newImport struct{ name, importPath string }
-	var newImports []newImport // for AddNamedImport
-	qual := func(pkg *types.Package) string {
-		// TODO(adonovan): don't ignore vendor prefix.
-		//
-		// Ignore the current package import.
-		if pkg.Path() == sym.Pkg().Path() {
-			return ""
-		}
-
-		importPath := ImportPath(pkg.Path())
-		name, ok := importEnv[importPath]
-		if !ok {
-			// Insert new import using package's declared name.
-			//
-			// TODO(adonovan): resolve conflict between declared
-			// name and existing file-level (declPGF.File.Imports)
-			// or package-level (sym.Pkg.Scope) decls by
-			// generating a fresh name.
-			name = pkg.Name()
-			importEnv[importPath] = name
-			new := newImport{importPath: string(importPath)}
-			// For clarity, use a renaming import whenever the
-			// local name does not match the path's last segment.
-			if name != pathpkg.Base(trimVersionSuffix(new.importPath)) {
-				new.name = name
-			}
-			newImports = append(newImports, new)
-		}
-		return name
-	}
-
+	newImports := make([]newImport, 0, len(declPGF.File.Imports))
+	qual := newNamedImportQual(declPGF, snapshot, declMeta, sym, func(imp newImport) {
+		newImports = append(newImports, imp)
+	})
 	// Compute insertion point for new declarations:
 	// after the top-level declaration enclosing the (package-level) type.
 	insertOffset, err := safetoken.Offset(declPGF.Tok, declPGF.File.End())
@@ -238,3 +185,148 @@ func trimVersionSuffix(path string) string {
 	}
 	return path
 }
+
+func insertStructField(ctx context.Context, snapshot *cache.Snapshot, mp *metadata.Package, fieldInfo *stubmethods.StructFieldInfo) (*token.FileSet, *analysis.SuggestedFix, error) {
+	if fieldInfo == nil {
+		return nil, nil, fmt.Errorf("no field info provided")
+	}
+
+	// get the file containing the struct definition using the position
+	declPGF, _, err := parseFull(ctx, snapshot, fieldInfo.Fset, fieldInfo.Named.Obj().Pos())
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to parse file declaring struct: %w", err)
+	}
+	if declPGF.Fixed() {
+		return nil, nil, fmt.Errorf("file contains parse errors: %s", declPGF.URI)
+	}
+
+	// find the struct type declaration
+	var structType *ast.StructType
+	ast.Inspect(declPGF.File, func(n ast.Node) bool {
+		if typeSpec, ok := n.(*ast.TypeSpec); ok {
+			if typeSpec.Name.Name == fieldInfo.Object.Name() {
+				if st, ok := typeSpec.Type.(*ast.StructType); ok {
+					structType = st
+					return false
+				}
+			}
+		}
+		return true
+	})
+
+	if structType == nil {
+		return nil, nil, fmt.Errorf("could not find struct definition")
+	}
+
+	// Find metadata for the symbol's declaring package
+	// as we'll need its import mapping.
+	declMeta := findFileInDeps(snapshot, mp, declPGF.URI)
+	if declMeta == nil {
+		return nil, nil, bug.Errorf("can't find metadata for file %s among dependencies of %s", declPGF.URI, mp)
+	}
+
+	qual := newNamedImportQual(declPGF, snapshot, declMeta, fieldInfo.Named.Obj(), func(imp newImport) { /* discard */ })
+
+	// find the position to insert the new field (end of struct fields)
+	insertPos := structType.Fields.Closing - 1
+	if insertPos == structType.Fields.Opening {
+		// struct has no fields yet
+		insertPos = structType.Fields.Closing
+	}
+
+	var buf bytes.Buffer
+	if err := fieldInfo.Emit(&buf, qual); err != nil {
+		return nil, nil, err
+	}
+
+	_, err = declPGF.Mapper.PosRange(declPGF.Tok, insertPos, insertPos)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	textEdit := analysis.TextEdit{
+		Pos:     insertPos,
+		End:     insertPos,
+		NewText: buf.Bytes(),
+	}
+
+	return fieldInfo.Fset, &analysis.SuggestedFix{
+		Message:   fmt.Sprintf("Add field %s to struct %s", fieldInfo.Expr.Sel.Name, fieldInfo.Named.Obj().Name()),
+		TextEdits: []analysis.TextEdit{textEdit},
+	}, nil
+}
+
+type newImport struct {
+	name       string
+	importPath string
+}
+
+func newNamedImportQual(declPGF *parsego.File, snapshot *cache.Snapshot, declMeta *metadata.Package, sym types.Object, newImportHandler func(imp newImport)) func(*types.Package) string {
+	// Build import environment for the declaring file.
+	// (typesinternal.FileQualifier works only for complete
+	// import mappings, and requires types.)
+	importEnv := make(map[ImportPath]string) // value is local name
+	for _, imp := range declPGF.File.Imports {
+		importPath := metadata.UnquoteImportPath(imp)
+		var name string
+		if imp.Name != nil {
+			name = imp.Name.Name
+			if name == "_" {
+				continue
+			} else if name == "." {
+				name = "" // see types.Qualifier
+			}
+		} else {
+			// Use the correct name from the metadata of the imported
+			// package---not a guess based on the import path.
+			mp := snapshot.Metadata(declMeta.DepsByImpPath[importPath])
+			if mp == nil {
+				continue // can't happen?
+			}
+			name = string(mp.Name)
+		}
+		importEnv[importPath] = name // latest alias wins
+	}
+
+	// Create a package name qualifier that uses the
+	// locally appropriate imported package name.
+	// It records any needed new imports.
+	// TODO(adonovan): factor with golang.FormatVarType?
+	//
+	// Prior to CL 469155 this logic preserved any renaming
+	// imports from the file that declares the interface
+	// method--ostensibly the preferred name for imports of
+	// frequently renamed packages such as protobufs.
+	// Now we use the package's declared name. If this turns out
+	// to be a mistake, then use parseHeader(si.iface.Pos()).
+	//
+	return func(pkg *types.Package) string {
+		// TODO(adonovan): don't ignore vendor prefix.
+		//
+		// Ignore the current package import.
+		if pkg.Path() == sym.Pkg().Path() {
+			return ""
+		}
+
+		importPath := ImportPath(pkg.Path())
+		name, ok := importEnv[importPath]
+		if !ok {
+			// Insert new import using package's declared name.
+			//
+			// TODO(adonovan): resolve conflict between declared
+			// name and existing file-level (declPGF.File.Imports)
+			// or package-level (sym.Pkg.Scope) decls by
+			// generating a fresh name.
+			name = pkg.Name()
+			importEnv[importPath] = name
+			new := newImport{importPath: string(importPath)}
+			// For clarity, use a renaming import whenever the
+			// local name does not match the path's last segment.
+			if name != pathpkg.Base(trimVersionSuffix(new.importPath)) {
+				new.name = name
+			}
+			newImportHandler(new)
+		}
+		return name
+	}
+}