Go compile errors '"fmt" imported and not used' and 'declared and not used' (x declared and not used): why does Go reject this and what is the correct fix?

Cause: Go treats an unused import or an unused local variable as a compile error, not a warning. The Go FAQ explains why: an unused variable can indicate a bug, and unused imports slow down compilation as a codebase grows. Common triggers are leftover debug code, a variable assigned but never read, a result you only use in a commented-out line, and := inside an if/for block creating a new shadowed variable that is never used while the outer one stays untouched. Fix: 1. Delete the unused import or variable. This is the right answer almost always. 2. Let tooling do it: goimports -w file.go (or gopls / your editor's organise-imports on save) adds and removes imports automatically. 3. If a function result is intentionally ignored, assign it to the blank identifier: _, err := f() or _ = g(). For errors, handle them instead of discarding. 4. If you have a shadowing bug (x := ... inside a block when you meant x = ...), use plain = to assign to the outer variable. 5. Importing only for side effects (a driver or pprof registration) is legal with a blank import: import _ "net/http/pprof". 6. While debugging only, Effective Go and the FAQ suggest placeholder lines such as var _ = fmt.Printf or _ = x with a comment, and removing them before committing. Note: the compiler only rejects unused local variables; unused function parameters, struct fields, constants and package-level variables are allowed. Verify: go build ./... and go vet ./... succeed with no errors. Sources: https://go.dev/doc/faq https://go.dev/doc/effective_go https://go.dev/ref/spec