nogo should provide a json tree with suggested fixes.

What version of rules_go are you using?

v0.36.0

What version of gazelle are you using?

v0.28.0

What version of Bazel are you using?

v5.3.2

Does this issue reproduce with the latest releases of all the above?

Yes

What operating system and processor architecture are you using?

Linux

Any other potentially useful information about your toolchain?

No

What did you do?

bazel build --output_groups=nogo_json_tree //path_to_target/...

What did you expect to see?

A json tree with suggested fixes from analyzers

What did you see instead?

Nothing.

Current state of the world

At the moment, nogo, creates a similar output to what an analyzer will output using the standard go toolchain if there is a diagnostic from any analyzer setup in nogo.

nogo output:

> bazel build …
bazel_workspace/example/example.go:43:3: This is an error message from our custom analyzer. (analyzer_name)

go unitchecker output:

> go run . example/example.go
example/example.go:43:3: This is an error message from our custom analyzer.

The error message from bazel is better as it contains the analyzer name; this becomes handy when there is more than one diagnostic.

Go analysis API provides suggested fixes as part of analysis.Diagnostic struct. These suggested fixes are used by unitchecker to fix the file.

In the latest version of https://pkg.go.dev/golang.org/x/tools there is a new -json flag that we can pass to unitchecker that will show us JSON with all the information needed to apply those fixes.

Example:

> go run . -json examples/example.go
{
   "command-line-arguments": {
       "useprint": [
           {
               "posn": "examples/example.go:10:2",
               "message": "update this line",
               "suggested_fixes": [ 
                   {
                       "message": "use fmt.Print() instead",
                       "edits": [
                           {
                               "filename": "/examples/example.go",
                               "start": 73,
                               "end": 93,
                               "new": "fmt.Print(\"hello\")"
                           }
                       ]
                   }
               ]
           }
       ]
   }
}

It is not part of nogo to apply those fixes, but we should be able to get this JSON tree and create a small tool that provides this functionality.

Proposal

Add a new option in --output_groups that outputs the value of this JSON tree.

> bazel build --output_groups=nogo_json_tree //path_to_target/...
{
   "nogo": {
       "custom_analyzer": [
           {
               "posn": "examples/example.go:10:2",
               "message": "update this line",
               "suggested_fixes": [ 
                   {
                       "message": "use fmt.Print() instead",
                       "edits": [
                           {
                               "filename": "/examples/example.go",
                               "start": 73,
                               "end": 93,
                               "new": "fmt.Print(\"hello\")"
                           }
                       ]
                   }
               ]
           }
       ]
   }
}

Start by tracing nogo's existing diagnostic output and the Bazel --output_groups handling; the issue does not name specific files or tests. Compare the Go analysis Diagnostic data and unitchecker -json output, then define the output-group path and verify that builds emit the requested JSON tree with suggested fixes.