Go "invalid go version" in go.mod - Fix the go Directive in CI

The go and toolchain directives in go.mod must follow a strict version format. A hand-edited or malformed value - wrong precision, a stray prefix, or an impossible version - makes the toolchain reject the file outright.

What this error means

A go command fails parsing go.mod with invalid go version "..." or go directive ... must match format 1.23. Nothing builds because Go cannot even read the module file.

go: errors parsing go.mod:
	/app/go.mod:3: invalid go version '1.21.0.1': must match format 1.23

Common causes

A malformed go directive

The go line was hand-edited to a value Go does not accept - too many components, a v prefix, or a non-existent version - so parsing fails.

A toolchain directive Go cannot use

A toolchain go1.X line with a bad format or a version the runner cannot obtain stops the command before the build.

How to fix it

Set a valid go directive

Use go mod edit so the directive is written in the exact format the toolchain expects.

go mod edit -go=1.23
go mod tidy

Fix or drop the toolchain line

Set a valid toolchain value, or remove it to let GOTOOLCHAIN handling decide.

go mod edit -toolchain=go1.23.2
# or remove it entirely
go mod edit -toolchain=none

How to prevent it

• Edit go/toolchain directives with go mod edit, not by hand.
• Keep the directive in the format Go expects (e.g. 1.23 or 1.23.2).
• Commit a tidy go.mod and verify it parses with go mod verify.

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