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cmd/go: add GODEBUG tokens for debugging lazy module loading

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GODEBUG=lazymod=log causes the go command to log a stack dump whenever
the full module graph is loaded in a lazy module.

GODEBUG=lazymod=strict does the same, but also terminates the command
with a nonzero exit code.

For #36460

Change-Id: Ia5a4c46069044bcc157b285f64c2392990d70bd0
Reviewed-on: https://go-review.googlesource.com/c/go/+/315411
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
This commit is contained in:
Bryan C. Mills 2021-04-30 01:29:57 -04:00
parent eb71887b99
commit cbff713e68
1 changed files with 19 additions and 0 deletions
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19
src/cmd/go/internal/modload/buildlist.go
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@ -11,8 +11,10 @@ import (
"cmd/go/internal/par" "cmd/go/internal/par"
"context" "context"
"fmt" "fmt"
"os"
"reflect" "reflect"
"runtime" "runtime"
"runtime/debug"
"strings" "strings"
"sync" "sync"
"sync/atomic" "sync/atomic"
@ -232,12 +234,29 @@ type summaryError struct {
err error err error
} }
var readModGraphDebugOnce sync.Once
// readModGraph reads and returns the module dependency graph starting at the // readModGraph reads and returns the module dependency graph starting at the
// given roots. // given roots.
// //
// Unlike LoadModGraph, readModGraph does not attempt to diagnose or update // Unlike LoadModGraph, readModGraph does not attempt to diagnose or update
// inconsistent roots. // inconsistent roots.
func readModGraph(ctx context.Context, depth modDepth, roots []module.Version) (*ModuleGraph, error) { func readModGraph(ctx context.Context, depth modDepth, roots []module.Version) (*ModuleGraph, error) {
if depth == lazy {
readModGraphDebugOnce.Do(func() {
for _, f := range strings.Split(os.Getenv("GODEBUG"), ",") {
switch f {
case "lazymod=log":
debug.PrintStack()
fmt.Fprintf(os.Stderr, "go: read full module graph.\n")
case "lazymod=strict":
debug.PrintStack()
base.Fatalf("go: read full module graph (forbidden by GODEBUG=lazymod=strict).")
}
}
})
}
var ( var (
mu sync.Mutex // guards mg.g and hasError during loading mu sync.Mutex // guards mg.g and hasError during loading
hasError bool hasError bool