- Move AppEngineTokenSource documentation to one location
- Add file comments
- Log the deprecation message exactly once in the second generation and
flex AppEngineTokenSource.
Go 1.11 on App Engine standard is a "second generation" runtime, and
second generation runtimes do not set the appengine build tag.
appengine_hook.go was behind the appengine build tag, meaning that
AppEngineTokenSource panicked on the go111 runtime, saying,
"AppEngineTokenSource can only be used on App Engine."
The second gen runtimes should use ComputeTokenSource, which is also
what flex does [1]. This commit does two things to remedy the situation:
1. Put the pre-existing implementation of AppEngineTokenSource behind
the appengine build tag since it only works on first gen App Engine
runtimes. This leaves first gen behavior unchanged.
2. Add a new implementation of AppEngineTokenSource and tag it
!appengine. This implementation will therefore be used by second gen
App Engine standard runtimes and App Engine flexible. It delegates
to ComputeTokenSource.
The new AppEngineTokenSource implementation emits a log message
informing the user that AppEngineTokenSource is deprecated for second
gen runtimes and flex, instructing them to use DefaultTokenSource or
ComputeTokenSource instead. The documentation is updated to say the
same.
In this way users will not break when upgrading from Go 1.9 to Go 1.11
on App Engine but they will be nudged toward the world where App Engine
runtimes have less special behavior.
findDefaultCredentials still calls AppEngineTokenSource for first gen
runtimes and ComputeTokenSource for flex.
Fixes#334
Test: I deployed an app that uses AppEngineTokenSource to Go 1.9 and
Go 1.11 on App Engine standard and to Go 1.11 on App Engine
flexible and it worked in all cases. Also verified that the log
message is present on go111 and flex.
[1] DefaultTokenSource did use ComputeTokenSource for flex but
AppEngineTokenSource did not. AppEngineTokenSource is supported on flex,
in the sense that it doesn't panic when used on flex in the way it does
when used outside App Engine. However, AppEngineTokenSource makes an API
call internally that isn't supported by default on flex, which emits a
log instructing the user to enable the compat runtime. The compat
runtimes are deprecated and deploys are blocked. This is a bad
experience. This commit has the side effect of fixing this.
Michael Traver