x/tools/gopls/internal/analysis/modernize: use strings.Cut

[adonovan]

[Update: CutPrefix was done by https://go.dev/cl/655777; this issue is now about strings.Cut.]

Replace:

if strings.HasPrefix(s, pre) { use(strings.TrimPrefix(s, pre)) }
-> 
if after, ok := strings.CutPrefix(s, pre); ok { use(after) } 

Variants:

• bytes package
• CutSuffix
• if rest := strings.TrimPrefix(s, pre); rest != s { use(rest) } -> ...

cc: @josharian

[josharian]

Also strings.Cut. If there's an idx := strings.Index(s, needle), and then the only expressions involving idx thereafter are idx < 0, idx >= 0, s[:idx], and s[idx+len(needle:] (possible with len(needle) as an int if needle is a constant), then those expressions can be replaced (as appropriate) by before, after, ok := strings.Cut(s, needle), ok, before, and after. Also strings.IndexByte. Mutatis mutandis for bytes.Cut.

[gopherbot]

Change https://go.dev/cl/655777 mentions this issue: gopls/internal/analysis/modernize: modernizer to suggest using strings.CutPrefix

[adonovan]

Oops, reopening for strings.Cut.