gcassert
gcassert is a program for making assertions about compiler decisions in Golang programs, via inline comment directives like //gcassert:inline.
Example
Given a file foo.go:
package foo
func addOne(i int) int {
return i+1
}
//gcassert:inline
func addTwo(i int) int {
return i+1
}
func a(ints []int) int {
var sum int
for i := range ints {
//gcassert:bce,inline
sum += addOne(ints[i])
sum += addTwo(ints[i]) //gcassert:bce
sum += ints[i] //gcassert:bce
}
return sum
}
The inline //gcassert directive will cause gcassert to fail if the line sum += addOne(ints[i]) is either not inlined or contains bounds checks.
A //gcassert:inline directive on a function will cause gcassert to fail if any of the callers of that function do not get inlined.
//gcassert comments expect a comma-separated list of directives after //gcassert:. They can be included above the line in question or after, as an inline comment.
Installation
go get github.com/jordanlewis/gcassert/cmd/gcassert
Usage
Run gcassert on packages containing gcassert directives, like this:
gcassert ./package/path
The program will output all lines that had a gcassert directive that wasn't respected by the compiler.
For example, running on the testdata directory in this library will produce the following output:
$ gcassert ./testdata
testdata/bce.go:8: fmt.Println(ints[5]): Found IsInBounds
testdata/bce.go:16: sum += notInlinable(ints[i]): call was not inlined
testdata/inline.go:22: sum += notInlinable(i): call was not inlined
Inspecting each of the listed lines will show a //gcassert directive that wasn't upheld when running the compiler on the package.
Directives
//gcassert:inline
The inline directive on a CallExpr asserts that the following statement contains a function that is inlined by the compiler. If the function does not get inlined, gcassert will fail.
The inline directive on a FuncDecl asserts that every caller of that function is actually inlined by the compiler
//gcassert:bce
The bce directive asserts that the following statement contains a slice index that has no necessary bounds checks. If the compiler adds bounds checks, gcassert will fail.
![[dnm] demonstrate that dead code hits assertions](https://avatars.githubusercontent.com/u/5438456?v=4)
