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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package modcmd
import (
"context"
"fmt"
"strings"
"cmd/go/internal/base"
"cmd/go/internal/imports"
"cmd/go/internal/modload"
"golang.org/x/mod/module"
)
var cmdWhy = &base.Command{
UsageLine: "go mod why [-m] [-vendor] packages...",
Short: "explain why packages or modules are needed",
Long: `
Why shows a shortest path in the import graph from the main module to
each of the listed packages. If the -m flag is given, why treats the
arguments as a list of modules and finds a path to any package in each
of the modules.
By default, why queries the graph of packages matched by "go list all",
which includes tests for reachable packages. The -vendor flag causes why
to exclude tests of dependencies.
The output is a sequence of stanzas, one for each package or module
name on the command line, separated by blank lines. Each stanza begins
with a comment line "# package" or "# module" giving the target
package or module. Subsequent lines give a path through the import
graph, one package per line. If the package or module is not
referenced from the main module, the stanza will display a single
parenthesized note indicating that fact.
For example:
$ go mod why golang.org/x/text/language golang.org/x/text/encoding
# golang.org/x/text/language
rsc.io/quote
rsc.io/sampler
golang.org/x/text/language
# golang.org/x/text/encoding
(main module does not need package golang.org/x/text/encoding)
$
See https://golang.org/ref/mod#go-mod-why for more about 'go mod why'.
`,
}
var (
whyM = cmdWhy.Flag.Bool("m", false, "")
whyVendor = cmdWhy.Flag.Bool("vendor", false, "")
)
func init() {
cmdWhy.Run = runWhy // break init cycle
base.AddModCommonFlags(&cmdWhy.Flag)
}
func runWhy(ctx context.Context, cmd *base.Command, args []string) {
modload.ForceUseModules = true
modload.RootMode = modload.NeedRoot
loadOpts := modload.PackageOpts{
Tags: imports.AnyTags(),
VendorModulesInGOROOTSrc: true,
LoadTests: !*whyVendor,
SilencePackageErrors: true,
UseVendorAll: *whyVendor,
}
if *whyM {
for _, arg := range args {
if strings.Contains(arg, "@") {
base.Fatalf("go mod why: module query not allowed")
}
}
mods, err := modload.ListModules(ctx, args, 0)
if err != nil {
base.Fatalf("go mod why: %v", err)
}
byModule := make(map[module.Version][]string)
_, pkgs := modload.LoadPackages(ctx, loadOpts, "all")
for _, path := range pkgs {
m := modload.PackageModule(path)
if m.Path != "" {
byModule[m] = append(byModule[m], path)
}
}
sep := ""
for _, m := range mods {
best := ""
bestDepth := 1000000000
for _, path := range byModule[module.Version{Path: m.Path, Version: m.Version}] {
d := modload.WhyDepth(path)
if d > 0 && d < bestDepth {
best = path
bestDepth = d
}
}
why := modload.Why(best)
if why == "" {
vendoring := ""
if *whyVendor {
vendoring = " to vendor"
}
why = "(main module does not need" + vendoring + " module " + m.Path + ")\n"
}
fmt.Printf("%s# %s\n%s", sep, m.Path, why)
sep = "\n"
}
} else {
// Resolve to packages.
matches, _ := modload.LoadPackages(ctx, loadOpts, args...)
modload.LoadPackages(ctx, loadOpts, "all") // rebuild graph, from main module (not from named packages)
sep := ""
for _, m := range matches {
for _, path := range m.Pkgs {
why := modload.Why(path)
if why == "" {
vendoring := ""
if *whyVendor {
vendoring = " to vendor"
}
why = "(main module does not need" + vendoring + " package " + path + ")\n"
}
fmt.Printf("%s# %s\n%s", sep, path, why)
sep = "\n"
}
}
}
}
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