x/tools/gopls: implement struct field generation quickfix

Author: dennypenta

gopls/doc/release/v0.17.0.md

@@ -92,3 +92,11 @@ from the context of the access.
 The new `yield` analyzer detects mistakes using the `yield` function
 in a Go 1.23 iterator, such as failure to check its boolean result and
 break out of a loop.
+
+## 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/stubmethods/stubcalledfunc.go

@@ -308,7 +308,7 @@ func TypesFromContext(info *types.Info, path []ast.Node, pos token.Pos) []types.
 							arg := callExpr.Args[0]
 							composite, ok := arg.(*ast.CompositeLit)
 							if ok {
-								t := typeFromCompositeLit(info, path, composite)
+								t := typeFromExpr(info, path, composite)
 								typs = append(typs, t)
 								break
 							}
@@ -325,7 +325,7 @@ func TypesFromContext(info *types.Info, path []ast.Node, pos token.Pos) []types.
 							arg := callExpr.Args[0]
 							composite, ok := arg.(*ast.CompositeLit)
 							if ok {
-								t := typeFromCompositeLit(info, path, composite)
+								t := typeFromExpr(info, path, composite)
 								t = types.NewPointer(t)
 								typs = append(typs, t)
 								break
@@ -345,23 +345,23 @@ func TypesFromContext(info *types.Info, path []ast.Node, pos token.Pos) []types.
 					// a variable
 					ident, ok := rh.(*ast.Ident)
 					if ok {
-						if t := typeFromIdent(info, path, ident); t != nil {
+						if t := typeFromExpr(info, path, ident); t != nil {
 							typs = append(typs, t)
 						}
 						break
 					}
 
 					selectorExpr, ok := rh.(*ast.SelectorExpr)
 					if ok {
-						if t := typeFromIdent(info, path, selectorExpr.Sel); t != nil {
+						if t := typeFromExpr(info, path, selectorExpr.Sel); t != nil {
 							typs = append(typs, t)
 						}
 						break
 					}
 					// composite
 					composite, ok := rh.(*ast.CompositeLit)
 					if ok {
-						t := typeFromCompositeLit(info, path, composite)
+						t := typeFromExpr(info, path, composite)
 						typs = append(typs, t)
 						break
 					}
@@ -386,7 +386,7 @@ func TypesFromContext(info *types.Info, path []ast.Node, pos token.Pos) []types.
 					if ok {
 						ident, ok := starExpr.X.(*ast.Ident)
 						if ok {
-							if t := typeFromIdent(info, path, ident); t != nil {
+							if t := typeFromExpr(info, path, ident); t != nil {
 								if pointer, ok := t.(*types.Pointer); ok {
 									t = pointer.Elem()
 								}
@@ -487,102 +487,54 @@ func lastSection(identName string) string {
 	}
 }
 
-func typeFromCompositeLit(info *types.Info, path []ast.Node, composite *ast.CompositeLit) types.Type {
-	if t := info.TypeOf(composite); t != nil {
-		if !containsInvalid(t) {
-			t = types.Default(t)
-			if named, ok := t.(*types.Named); ok {
-				if pkg := named.Obj().Pkg(); pkg != nil {
-					// Find the file in the path that contains this assignment
-					var file *ast.File
-					for _, n := range path {
-						if f, ok := n.(*ast.File); ok {
-							file = f
-							break
-						}
-					}
-
-					if file != nil {
-						// Look for any import spec that imports this package
-						var pkgName string
-						for _, imp := range file.Imports {
-							if path, _ := strconv.Unquote(imp.Path.Value); path == pkg.Path() {
-								// Use the alias if specified, otherwise use package name
-								if imp.Name != nil {
-									pkgName = imp.Name.Name
-								} else {
-									pkgName = pkg.Name()
-								}
-								break
-							}
-						}
-						if pkgName == "" {
-							pkgName = pkg.Name() // fallback to package name if no import found
-						}
+func typeFromExpr(info *types.Info, path []ast.Node, expr ast.Expr) types.Type {
+	t := info.TypeOf(expr)
+	if t == nil {
+		return nil
+	}
 
-						// Create new package with the correct name (either alias or original)
-						newPkg := types.NewPackage(pkgName, pkgName)
-						newName := types.NewTypeName(named.Obj().Pos(), newPkg, named.Obj().Name(), nil)
-						t = types.NewNamed(newName, named.Underlying(), nil)
+	if !containsInvalid(t) {
+		t = types.Default(t)
+		if named, ok := t.(*types.Named); ok {
+			if pkg := named.Obj().Pkg(); pkg != nil {
+				// find the file in the path that contains this assignment
+				var file *ast.File
+				for _, n := range path {
+					if f, ok := n.(*ast.File); ok {
+						file = f
+						break
 					}
 				}
-				return t
-			}
-		} else {
-			t = anyType
-		}
-		return t
-	}
-	return nil
-}
 
-func typeFromIdent(info *types.Info, path []ast.Node, ident *ast.Ident) types.Type {
-	if t := info.TypeOf(ident); t != nil {
-		if !containsInvalid(t) {
-			t = types.Default(t)
-			if named, ok := t.(*types.Named); ok {
-				if pkg := named.Obj().Pkg(); pkg != nil {
-					// find the file in the path that contains this assignment
-					var file *ast.File
-					for _, n := range path {
-						if f, ok := n.(*ast.File); ok {
-							file = f
+				if file != nil {
+					// look for any import spec that imports this package
+					var pkgName string
+					for _, imp := range file.Imports {
+						if path, _ := strconv.Unquote(imp.Path.Value); path == pkg.Path() {
+							// use the alias if specified, otherwise use package name
+							if imp.Name != nil {
+								pkgName = imp.Name.Name
+							} else {
+								pkgName = pkg.Name()
+							}
 							break
 						}
 					}
-
-					if file != nil {
-						// look for any import spec that imports this package
-						var pkgName string
-						for _, imp := range file.Imports {
-							if path, _ := strconv.Unquote(imp.Path.Value); path == pkg.Path() {
-								// use the alias if specified, otherwise use package name
-								if imp.Name != nil {
-									pkgName = imp.Name.Name
-								} else {
-									pkgName = pkg.Name()
-								}
-								break
-							}
-						}
-						// fallback to package name if no import found
-						if pkgName == "" {
-							pkgName = pkg.Name()
-						}
-
-						// create new package with the correct name (either alias or original)
-						newPkg := types.NewPackage(pkgName, pkgName)
-						newName := types.NewTypeName(named.Obj().Pos(), newPkg, named.Obj().Name(), nil)
-						t = types.NewNamed(newName, named.Underlying(), nil)
+					// fallback to package name if no import found
+					if pkgName == "" {
+						pkgName = pkg.Name()
 					}
+
+					// create new package with the correct name (either alias or original)
+					newPkg := types.NewPackage(pkgName, pkgName)
+					newName := types.NewTypeName(named.Obj().Pos(), newPkg, named.Obj().Name(), nil)
+					t = types.NewNamed(newName, named.Underlying(), nil)
 				}
-				return t
 			}
-		} else {
-			t = anyType
+			return t
 		}
-		return t
+	} else {
+		t = anyType
 	}
-
-	return nil
+	return t
 }