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testing: coverage calculation is wrong when runtime error occurs #62258
Description
What version of Go are you using (go version)?
$ go version
go1.20.5 linux/amd64Does this issue reproduce with the latest release?
YES
What operating system and processor architecture are you using (go env)?
$ go env
<details><summary><code>GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jade/.cache/go-build"
GOENV="/home/jade/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jade/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jade/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.20.5"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/jade/pasercover/go.mod"
GOWORK=""
CGO_CFLAGS="-O2 -g"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-O2 -g"
CGO_FFLAGS="-O2 -g"
CGO_LDFLAGS="-O2 -g"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3250049939=/tmp/go-build -gno-record-gcc-switches"
</code> Output</summary><br><pre>
$ go env
</pre></details>What did you do?
Here is the code to reproduce the issue.
package main
import (
"fmt"
)
type Node struct {
data int
next *Node
}
type LinkedList struct {
head *Node
}
func (ll *LinkedList) Insert(data int) {
newNode := &Node{data: data, next: nil}
if ll.head == nil {
ll.head = newNode
} else {
current := ll.head
for current.next != nil {
current = current.next
}
current.next = newNode
}
}
func (ll *LinkedList) Display() {
current := ll.head
for current != nil {
fmt.Printf("%d ", current.data)
current = current.next
}
fmt.Println()
}
func main() {
divideByZero()
fmt.Println("Main function continues to execute...")
}
func divideByZero() {
defer func() {
if err := recover(); err != nil {
fmt.Println("Recovered from:", err)
}
}()
n := Node{1, nil}
fmt.Println("Result:")
fmt.Println("Result:")
fmt.Println(n.next.data)
// lines below will be included in coverage, even n.next.data will trigger a nil error.
fmt.Println("Result:")
fmt.Println("Result:")
fmt.Println("Result:")
fmt.Println("Result:")
fmt.Println("Result:")
fmt.Println("Result:")
}What did you expect to see?
Lines below "fmt.Println(n.next.data)" will be excluded from the coverage.
What did you see instead?
parsecover.go:146: divideByZero 100.0%
Activity
[-]testing/cover: If an error occurs in a line of code while calculating code coverage, the code that follows this line within the same code block will still be included in the coverage calculation.[/-][+]testing/cover: Coverage calculation is wrong when runtime error occurs[/+][-]testing/cover: Coverage calculation is wrong when runtime error occurs[/-][+]testing: coverage calculation is wrong when runtime error occurs[/+]cagedmantis commentedon Aug 24, 2023
Can you include the code for parsecover.go? Which command are you running to retrieve coverage data?
Eiwinda commentedon Aug 25, 2023
The code posted above is parsecover.go.
I use
go build -cover -o myprogram parsecover.goGOCOVERDIR=./hhh ./myprogramgo tool covdata textfmt -i=hhh -o profile.txtgo tool cover -func=profile.txtrobpike commentedon Aug 25, 2023
Since coverage calculation is block-based, it assumes that all statements in a (branch-free) block will be executed. Without making the generated coverage code more fine-grained and inefficient, this would be hard to fix. It is an unusual enough case that it doesn't seem worth fixing.