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cmd/cover: misleading coverage indicators for channel operations in 'select' statements #27015

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MichaelS11 opened this issue Aug 16, 2018 · 1 comment
Open

cmd/cover: misleading coverage indicators for channel operations in 'select' statements #27015

MichaelS11 opened this issue Aug 16, 2018 · 1 comment
Labels
compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Unplanned

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@MichaelS11
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What version of Go are you using (go version)?

go version go1.10.3 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

set GOHOSTARCH=amd64
set GOHOSTOS=windows

What did you do?

main.go:

package main

import (
	"fmt"
	"time"
)

var vars struct {
	chanStruct    chan struct{}
	chanInt       chan int
	chanOneClosed chan struct{}
	spamNumber    int
}

func main() {
	vars.chanStruct = make(chan struct{})
	vars.chanInt = make(chan int, 1024)
	vars.chanOneClosed = make(chan struct{})
	vars.spamNumber = 20

	go feed()
	go aLoop()

	time.Sleep(time.Second)

	close(vars.chanStruct)

	select {
	case <-vars.chanOneClosed:
	}

	time.Sleep(time.Second)
}

// a comment
func feed() {
	// a comment
	for i := 0; i < 10; i++ {
		// a comment
		vars.chanInt <- i
		// a comment
	}
	// a comment
}

// a comment
func aLoop() {
Loop:
	// a comment
	for {
		// a comment
		select {
		// a comment
		case <-vars.chanStruct:
			// a comment
			close(vars.chanOneClosed)
			// a comment
			break Loop
		// a comment
		case myInt := <-vars.chanInt:
			// a comment
			if myInt < vars.spamNumber {
				// a comment
				vars.chanInt <- myInt + 1
				// a comment
			}
			// a comment
		}
		// a comment
	}
	// a comment
	fmt.Println("closed")
	// a comment
}

main_test.go:

package main

import (
	"testing"
	"time"
)

func TestALoop(t *testing.T) {
	vars.chanStruct = make(chan struct{})
	vars.chanInt = make(chan int, 1024)
	vars.chanOneClosed = make(chan struct{})
	vars.spamNumber = 20

	go feed()
	go aLoop()

	time.Sleep(time.Second)

	close(vars.chanStruct)

	select {
	case <-vars.chanOneClosed:
	}

	time.Sleep(time.Second)
}

Then run:

go test -coverprofile=coverage.out -v test
go tool cover -html=coverage.out

What did you expect to see?

Coverage report with green and black, with only red in main, similar to this:

image

Note, remove the follow code from main to get coverage report to be "correct"

	close(vars.chanStruct)

	select {
	case <-vars.chanOneClosed:
	}

	time.Sleep(time.Second)

What did you see instead?

Coverage report with red marks in comments, function, and case:

image

Note:

This is similar to #22545 but that one is only comments.
@andybons andybons changed the title test / tool cover: coverprofile / coverage report incorrect red coverage cmd/go: test / tool cover: coverprofile / coverage report incorrect red coverage Aug 16, 2018
@andybons andybons added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 16, 2018
@andybons andybons added this to the Unplanned milestone Aug 16, 2018
@chrisreedy chrisreedy mentioned this issue Oct 22, 2018
Open
@bcmills bcmills changed the title cmd/go: test / tool cover: coverprofile / coverage report incorrect red coverage cmd/cover: misleading coverage indicators for channel operations in 'select' statements Jan 18, 2019
@bcmills
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bcmills commented Jan 18, 2019

Let's address one symptom per issue, please. #22545 already addresses the missing comments, so we'll make this one about the missing channel ops.

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
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Labels
compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@andybons @bcmills @gopherbot @MichaelS11