Introduce autofix API

helper/runner.go

@@ -318,6 +318,11 @@ func (r *Runner) EmitIssue(rule tflint.Rule, message string, location hcl.Range)
 	return nil
 }
 
+func (r *Runner) EmitIssueWithFix(rule tflint.Rule, message string, location hcl.Range, fixFunc func(f *tflint.Fixer) error) error {
+	// TODO: Implement
+	return nil
+}
+
 // EnsureNoError is a method that simply runs a function if there is no error.
 //
 // Deprecated: Use EvaluateExpr with a function callback. e.g. EvaluateExpr(expr, func (val T) error {}, ...)

plugin/host2plugin/server.go

@@ -116,7 +116,13 @@ func (s *GRPCServer) Check(ctx context.Context, req *proto.Check_Request) (*prot
 	}
 	defer conn.Close()
 
-	runner, err := s.impl.NewRunner(&plugin2host.GRPCClient{Client: proto.NewRunnerClient(conn)})
+	client := proto.NewRunnerClient(conn)
+	resp, err := client.GetFiles(ctx, &proto.GetFiles_Request{})
+	if err != nil {
+		return nil, toproto.Error(codes.FailedPrecondition, err)
+	}
+
+	runner, err := s.impl.NewRunner(&plugin2host.GRPCClient{Client: client, Fixer: tflint.NewFixer(resp.Files)})
 	if err != nil {
 		return nil, toproto.Error(codes.FailedPrecondition, err)
 	}

plugin/plugin2host/client.go

@@ -28,6 +28,7 @@ import (
 // GRPCClient is a plugin-side implementation. Plugin can send requests through the client to host's gRPC server.
 type GRPCClient struct {
 	Client proto.RunnerClient
+	Fixer  *tflint.Fixer
 }
 
 var _ tflint.Runner = &GRPCClient{}
@@ -423,6 +424,20 @@ func (c *GRPCClient) EmitIssue(rule tflint.Rule, message string, location hcl.Ra
 	return nil
 }
 
+func (c *GRPCClient) EmitIssueWithFix(rule tflint.Rule, message string, location hcl.Range, fixFunc func(f *tflint.Fixer) error) error {
+	if err := fixFunc(c.Fixer); err != nil {
+		return err
+	}
+
+	_, err := c.Client.EmitIssue(context.Background(), &proto.EmitIssue_Request{Rule: toproto.Rule(rule), Message: message, Range: toproto.Range(location), Fixed: c.Fixer.Changes()})
+	if err != nil {
+		return fromproto.Error(err)
+	}
+	// TODO: ApplyChanges() should be called if the issue is not ignored.
+	c.Fixer.ApplyChanges()
+	return nil
+}
+
 // EnsureNoError is a helper for error handling. Depending on the type of error generated by EvaluateExpr,
 // determine whether to exit, skip, or continue. If it is continued, the passed function will be executed.
 //

plugin/proto/tflint.proto

@@ -207,6 +207,7 @@ message EmitIssue {
         Rule rule = 1;
         string message = 2;
         Range range = 3;
+        map<string, bytes> fixed = 4;
     }
     message Response {}
 }

tflint/fixer.go

@@ -0,0 +1,47 @@
+package tflint
+
+import (
+	"bytes"
+
+	"github.com/hashicorp/hcl/v2"
+)
+
+type Fixer struct {
+	sources map[string][]byte
+	changes map[string][]byte
+}
+
+func NewFixer(sources map[string][]byte) *Fixer {
+	return &Fixer{
+		sources: sources,
+		changes: map[string][]byte{},
+	}
+}
+
+func (f *Fixer) Replace(rng hcl.Range, replaced string) error {
+	original := f.sources[rng.Filename]
+	file := make([]byte, len(original))
+	copy(file, original)
+
+	// TODO: track byte index changes
+	buf := bytes.NewBuffer(file[:rng.Start.Byte])
+	buf.WriteString(replaced)
+	buf.Write(file[rng.End.Byte:])
+
+	if bytes.Equal(original, buf.Bytes()) {
+		return nil
+	}
+	f.changes[rng.Filename] = buf.Bytes()
+	return nil
+}
+
+func (f *Fixer) Changes() map[string][]byte {
+	return f.changes
+}
+
+func (f *Fixer) ApplyChanges() {
+	for filename, content := range f.changes {
+		f.sources[filename] = content
+	}
+	f.changes = map[string][]byte{}
+}

tflint/interface.go

@@ -227,6 +227,8 @@ type Runner interface {
 	// EmitIssue sends an issue to TFLint. You need to pass the message of the issue and the range.
 	EmitIssue(rule Rule, message string, issueRange hcl.Range) error
 
+	EmitIssueWithFix(rule Rule, message string, issueRange hcl.Range, fixFunc func(f *Fixer) error) error
+
 	// EnsureNoError is a helper for error handling. Depending on the type of error generated by EvaluateExpr,
 	// determine whether to exit, skip, or continue. If it is continued, the passed function will be executed.
 	//