x/tools/gopls: Reports for redundant type conversion

[pepehandsjpg]

Problem
Sometimes you can miss redundant type conversion in your code.

var ids []int32
for _, groups := range groupsCollection {
    if len(groups) > 0 {
        ids = append(ids, int32(groups[0])) // groups[0] is already int32  so there is unnecessary conversion
    }
}

Solution
Could you add warnings about unnecessary type conversion as it is done in goland

[findleyr]

See also dominikh/go-tools#936.

The concern expressed there remains: if gopls is only considering a single set of build tags, this analyzer may produce false positives.

I wonder how problematic those false positives would be. I also wonder how hard it would be to eliminate false positives by avoiding cases that could be affected by build tags.

CC @dominikh @mdempsky