Fix undercounting of coverage for lines in multiple blocks.

[eaburns]

The coverprofile format uses both lines and columns. It can report coverage for the same line across multiple blocks, if the column ranges do not overlap. The coverage counts should be summed, not assigned.

Here is an example:

c.go

package c

func False() bool { return false }

func F() int {
    if False() {
        return 1
    }
    return 2
}

c_test.go

package c

import "testing"

func TestF(t *testing.T) { F() }

The return 1 is never tested, but the call to False() is tested.

The coverprofile is:

mode: set
test/c/c.go:3.19,3.35 1 1
test/c/c.go:5.14,6.13 1 1
test/c/c.go:9.2,9.10 1 1
test/c/c.go:6.13,8.3 1 0

Line 6, the condition of the if-statement, is accounted for in two blocks. The first refers to the statement False(), the second refers to the beginning { of the block. The count of 0 for the un-covered return 1 was over-writing the count of 1 for the covered False(), causing the coverage to be under-counted.

Fixes #61

[eaburns]

Can you think of a good way to test this?

[eaburns]

I tried it out and it seems to work: https://coveralls.io/builds/5279120/source?filename=edit%2Fedit.go. But it still reports the closing brace as uncovered. I'll see if I can fix that.

[eaburns]

I think that this is the best we will get. Coverall computes line-level coverage, but go tool cover computes a finer-grained statement-level coverage.

[eaburns]

Here's an option that handles the case where there are more lines than statements by only counting the middle block of NumStmt lines: master...eaburns:issue61_statements.

I'm trying it out now.

[eaburns]

I think that it's best not to do master...eaburns:issue61_statements. It's a bit of a hack. Better to have correct line-level coverage than incorrect statement-level coverage.

This is ready for your review.

[mattn]

I'm thinking closing brace should not be passed. So I guess your patch works well.

[eaburns]

I think this is good to merge, if you are happy with it.

[mattn]

Thanks.