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Provide Fx types before user types #1191

Merged
merged 2 commits into from
Apr 19, 2024
Merged

Provide Fx types before user types #1191

merged 2 commits into from
Apr 19, 2024

Commits on Apr 19, 2024

  1. Provide internal types first 

    Consider the following example:
```go
func opts() fx.Option {
        return fx.Options(
                fx.WithLogger(func(fx.Lifecycle) fxevent.Logger {
                        return &fxevent.ConsoleLogger{ W: os.Stdout }
                }),
                fx.Provide(func() string { return "" }),
                fx.Provide(func() string { return "" }),
        )
}

func main() {
        fx.New(opts()).Run()
}
```

The relevant issue to surface to the user is that they are double providing
the same type. However, the actual error message is:
```
[Fx] ERROR              Failed to start: the following errors occurred:
 -  fx.Provide(main.opts.func3()) from:
    main.opts
        /home/user/go/src/scratch/fx_provide_order/main.go:17
    main.main
        /home/user/go/src/scratch/fx_provide_order/main.go:22
    runtime.main
        /opt/go/root/src/runtime/proc.go:271
    Failed: cannot provide function "main".opts.func3
(/home/user/go/src/scratch/fx_provide_order/main.go:17): cannot provide
string from [0]: already provided by "main".opts.func2
(/home/user/go/src/scratch/fx_provide_order/main.go:16)
 -  could not build arguments for function
"go.uber.org/fx".(*module).constructCustomLogger.func2
        /home/user/go-repos/pkg/mod/go.uber.org/fx@v1.21.0/module.go:292:
    failed to build fxevent.Logger:
    missing dependencies for function "main".opts.func1
        /home/user/go/src/scratch/fx_provide_order/main.go:11:
    missing type:
        - fx.Lifecycle (did you mean to Provide it?)
```
Which contains an additional error related to how the custom logger
could not be built.

This is because Fx will try to continue to build the custom logger
in the face of DI failure, theoretically to report issues
through the right channels. But after an error occurs when
providing anything, Fx refuses to provide any more types - leading to
a subsequent error when trying to build this custom logger
that depends on the `fx.Lifecycle` type.

This is a common issue that can be misleading for new engineers
debugging their fx apps.

I couldn't find any particular reason why user-provided provides
are registered before these Fx types, se this PR switches this ordering
so that custom loggers can still be built if they rely on the Fx types,
which cleans up the error message:
```
[Fx] ERROR              Failed to start: fx.Provide(main.opts.func3())
from:
main.opts
        /home/user/go/src/scratch/fx_provide_order/main.go:17
main.main
        /home/user/go/src/scratch/fx_provide_order/main.go:22
runtime.main
        /opt/go/root/src/runtime/proc.go:271
Failed: cannot provide function "main".opts.func3
(/home/user/go/src/scratch/fx_provide_order/main.go:17): cannot provide
string from [0]: already provided by "main".opts.func2
(/home/user/go/src/scratch/fx_provide_order/main.go:16)
```
    @JacobOaks
    JacobOaks committed Apr 19, 2024
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  2. fix typo

    @JacobOaks
    JacobOaks committed Apr 19, 2024
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    4626474 View commit details
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