proposal: runtime: add `GetEntryInfo` function

[timandy]

Proposal Details

Some time we want to get the entry info like module name. entry file path, dpendent modules and so on.
before go1.23 these infos can be get from runtime.firstmoduledata, but after go1.23 runtime.firstmoduledata can not be access.

before go1.23

// get path of the entry file, may be a /xx/xx_test.go or /xx/main.go
func getEntryFilePath() string {
	mainFile := getMainFile()
	if !isTestMode(mainFile) {
		return mainFile
	}
	firstModule := unsafe.Pointer(&firstmoduledata)
	fileTab := *(*[]byte)(reflection.Add(firstModule, filetabField.Offset))
	lastFiles := getLastFiles(fileTab)
	for _, file := range lastFiles {
		if isTestFile(file) {
			return file
		}
	}
	panic("can not found entry file path")
}

[gabyhelp]

Related Issues and Documentation

• proposal: runtime: add `go:linkname` on `runtime.firstmoduledata` #68581 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

I feel like debug.ReadBuildInfo and runtime.Caller already solved that problem.

[timandy]

@tdakkota debug.ReadBuildInfo() can not get entry path, and it return nothing in test mode.

if invoke runtime.Caller() in init() also can not get the stack frame of main or test_main

[seankhliao]

this describes the desired change, but not why this information should be exposed, what it would be used for, and how common a need for this is

[timandy]

@seankhliao One of the methods in our base library can read the specified configuration file in the root directory of the module where the entry file is located. The profile is not embedded into the binary. And test mod should be supoorted, so we need to know where the entry file is located at.

[jaloren]

@timandy you’ve described what you are doing but you haven’t explained why. could you explain what problem you are trying to solve?

[ianlancetaylor]

I don't understand how getting the path of the source file that contains main.main will tell you the root directory of the module. Many modules store commands, and main.main symbols, in subdirectories under cmd.

[timandy]

I don't understand how getting the path of the source file that contains main.main will tell you the root directory of the module. Many modules store commands, and main.main symbols, in subdirectories under cmd.

@ianlancetaylor Although many packages may contain the the _test.go file, I just need the first loaded at runtime;
That's why before go1.23, I needed to read firstmoduledata to get the list of loaded files and find the path to the first _test.go file; Then traverse the folder upwards until the go.mod file is found; Because our project definitely includes go.mod, there is no compatibility with older project sturcture;

[seankhliao]

go test executes the tests from the working directory containing the test, you could just use os.Getwd to get the directory of the package. If you built the test to execute elsewhere with go test -c, then i don't see how knowing the source code path helps you find the data you need.

[timandy]

@seankhliao As you said that go test -c is used for us during test time. We use cross compilation and then run unit tests by qemu-user-static.