Go Runtime Updater

1. Determine The Target Version

If the user did not give an explicit target, determine the latest exact stable Go version first.

1. Check pkg.go.dev/std and read the Version: goX.Y.Z line. Treat that as the latest exact stable release.
2. Do not infer the latest Go version from arbitrary pkg.go.dev search results or a random package page. Use pkg.go.dev/std.
3. Derive the latest release line from that exact version by replacing the patch with .0. Example: go1.26.1 maps to release line 1.26.0.
4. Derive the previous major release line by subtracting 1 from the minor version and using patch .0. Example: if the latest release line is 1.26.0, the previous major release line is 1.25.0.
5. When updating a go directive, use the relevant release line with patch .0, not the latest patch release.

2. Update go.mod And go.work

1. If a toolchain go... directive exists and the user wants the latest version, update only toolchain to the latest exact release. Do not change go. Use go mod edit -toolchain=goX.Y.Z or go work edit -toolchain=goX.Y.Z.
2. If a toolchain go... directive exists and the user wants a specific version, update only toolchain to that version. Do not change go. Use go mod edit -toolchain=goX.Y.Z or go work edit -toolchain=goX.Y.Z.
3. If there is no toolchain directive and the user wants a specific version that is not the latest release line, update go to that release line with patch .0. Use go mod edit -go=X.Y.0 or go work edit -go=X.Y.0.
4. If there is no toolchain directive and the user wants the latest version or latest major version, ask whether they want to raise the minimum supported Go version or keep compatibility by adding a toolchain directive instead.
5. Do not add a new toolchain directive unless the user asks for it or confirms that they want the latest toolchain without raising the minimum supported Go version.
6. Preserve formatting and unrelated directives.

3. Best Practice

1. go is the minimum required Go version.
2. toolchain is a suggested toolchain for working in the module or workspace.
3. Do not add toolchain by default; use it when the project wants a newer preferred toolchain without changing the minimum supported Go version.

4. Examples

1. Latest exact release is go1.26.1, file has go 1.25.0 and toolchain go1.25.7: update only to toolchain go1.26.1.
2. User requests 1.24.6, file has only go 1.23.0: update to go 1.24.0.
3. User requests "latest", file has only go 1.25.0: ask whether to change the minimum supported version to go 1.26.0 or add toolchain go1.26.1.
4. Latest exact release is go1.26.1: the previous major release line is 1.25.0.