feat: add --replace flag to ftl init go (#851)

This is mostly useful for local development on FTL itself, including
integration tests, where we need to replace the ftl import with local
ftl source.

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

cmd/ftl/cmd_init.go

@@ -30,8 +30,9 @@ type initCmd struct {
 }
 
 type initGoCmd struct {
-	Dir  string `arg:"" help:"Directory to initialize the module in."`
-	Name string `arg:"" help:"Name of the FTL module to create underneath the base directory."`
+	Replace map[string]string `short:"r" help:"Replace a module import path with a local path in the initialised FTL module." placeholder:"OLD=NEW,..."`
+	Dir     string            `arg:"" help:"Directory to initialize the module in."`
+	Name    string            `arg:"" help:"Name of the FTL module to create underneath the base directory."`
 }
 
 func (i initGoCmd) Run(ctx context.Context, parent *initCmd) error {

go-runtime/scaffolding/go.mod

@@ -1,4 +1,4 @@
 // This needs to exist so that the Go toolchain doesn't include this directory. Annoying.
 module exclude
 
-go 1.21.6
+go 1.21.6

go-runtime/scaffolding/{{ .Name | camel | lower }}/go.mod.tmpl

@@ -2,4 +2,8 @@ module ftl/{{ .Name }}
 
 go 1.21
 
-require github.com/TBD54566975/ftl latest
+require github.com/TBD54566975/ftl latest
+
+{{- range $old, $new := .Replace }}
+replace {{ $old }} => {{ $new }}
+{{- end }}