cmd/go: test Example with wrong type results in unclear error message

[gertcuykens]

GO111MODULE="on"
create a new module

module github.com/t/crypto
go 1.14

Although I think modules have nothing to do with it

Create a test file that contains a Example, and deliberately give it the wrong function definition like so

func ExampleCipherBlock(b []byte) {
  fmt.Println("hello")
  // Output:
}

% go test -v
# github.com/t/crypto.test
/var/folders/dv/8tlwvjr91zjdyq4rk14lkkfm0000gn/T/go-build917091680/b001/_testmain.go:30:30: cannot use crypto.ExampleCipherBlock (type func([]byte)) as type func() in field value
FAIL    github.com/t/crypto [build failed]

Now do the same but make a other error like so

k
func ExampleCipherBlock() {
  fmt.Println("hello")
  // Output:
}

% go test -v
# github.com/t/crypto
block_test.go:10:1: expected declaration, found k
FAIL    github.com/t/crypto [setup failed]
gert@mac crypto % 

Second one is the kind of error messages I expect, the first one completely messes up vscode because there is no way vscode can figure out where to point to.

[jayconrod]

In cmd/go/internal/load/test.go, we extract TestMain, Test, and Benchmark functions and check their signatures with checkTestFunc. We should do the same with examples but we extract those with go/doc.Examples and don't check the signatures.

The error should look like;

block_test.go:10:1: wrong signature for ExampleCipherBlock, must be: func ExampleCipherBlock()`

[jayconrod]

cc @dmitshur

[mohamednizar]

@jayconrod , I whish to contribute to this issue. How can start work on this ? I have started working on this.

[jayconrod]

Hey @mohamednizar, if you're interested in working on this, please follow the instructions in https://golang.org/doc/contribute.html for submitting a Gerrit CL or GitHub PR.

Any fix should include a small regression test in cmd/go/testdata/script. See the README there for information on writing tests.

[gopherbot]

Change https://golang.org/cl/211357 mentions this issue: go/doc: ignore example functions with arguments