Why Do Blank Lines After `// build` Directives Matter in Go Conditional Compilation?

Conditional Compilation in Go: Resolving Build Failures with Blank Lines

When customizing build behavior based on specific conditions in Go, conditional compilation plays a crucial role. However, improper usage can lead to compilation errors. Let's delve into an issue and its resolution to understand the correct approach to conditional compilation.

The issue pertains to the inability to successfully compile multiple Go packages with conditional constraints. The code includes two packages (main1.go and main2.go) with // build constraints and a -tags flag passed during compilation. However, the go build command results in a compilation error indicating that main is redeclared.

To rectify the issue, it's essential to note that a blank line must follow the // build constraint. This requirement, though not clearly documented, is evident in the source code.

The corrected code below demonstrates the correct usage of blank lines after // build constraints:

// +build main1

package main

import (
    "fmt"
)

func main() {
    fmt.Println("This is main 1")
}

// +build main2

package main

import (
    "fmt"
)

func main() {
    fmt.Println("This is main 2")
}

With the addition of blank lines, the compilation should now succeed without errors.

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