cmd/go: test that graph, verify, and why don't write go.mod or go.sum

They should also not report an error if these files need to be
updated. These commands are used for debugging, so it's important that
they still work when go.mod and go.sum are incomplete.

For #40775

Change-Id: I1b731599e5a4510f47827b9812525636a7402bf4
Reviewed-on: https://go-review.googlesource.com/c/go/+/351468
Trust: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/cmd/go/testdata/script/mod_skip_write.txt b/src/cmd/go/testdata/script/mod_skip_write.txt
new file mode 100644 (file)
index 0000000..c3e5906
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_skip_write.txt
@@ -0,0 +1,96 @@
+# Commands used to debug the module graph should not write go.mod or go.sum
+# or report errors when those files need to be updated.
+
+# Everything's okay initially.
+go list -m all
+
+# Downgrading sampler makes go.mod inconsistent, but 'go mod graph',
+# 'go mod verify', and 'go mod why' still work.
+cp go.mod go.mod.orig
+go mod edit -require=rsc.io/sampler@v1.2.0
+cp go.mod go.mod.edit
+! go list -m all
+stderr 'updates to go.mod needed'
+
+go mod graph
+cmp stdout graph.want
+cmp go.mod go.mod.edit
+
+go mod verify
+stdout '^all modules verified$'
+cmp go.mod go.mod.edit
+
+go mod why rsc.io/sampler
+cmp stdout why.want
+cmp go.mod go.mod.edit
+
+# TODO(#48613): 'go mod why -m' incorrectly reports sampler is not needed.
+go mod why -m rsc.io/sampler
+cmp stdout why-broken.want
+cmp go.mod go.mod.edit
+
+cp go.mod.orig go.mod
+
+# Removing go.sum breaks other commands, but 'go mod graph' and
+# 'go mod why' still work.
+rm go.sum
+! go list -m all
+stderr 'missing go.sum entry'
+
+go mod graph
+cmp stdout graph.want
+! exists go.sum
+
+go mod verify
+stdout '^all modules verified$'
+! exists go.sum
+
+go mod why rsc.io/sampler
+cmp stdout why.want
+! exists go.sum
+
+go mod why -m rsc.io/sampler
+cmp stdout why.want
+! exists go.sum
+
+-- go.mod --
+module m
+
+go 1.18
+
+require rsc.io/quote v1.5.2
+
+require (
+       golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
+       rsc.io/sampler v1.3.0 // indirect
+       rsc.io/testonly v1.0.0 // indirect
+)
+-- go.sum --
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:pvCbr/wm8HzDD3fVywevekufpn6tCGPY3spdHeZJEsw=
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+rsc.io/quote v1.5.2 h1:3fEykkD9k7lYzXqCYrwGAf7iNhbk4yCjHmKBN9td4L0=
+rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
+rsc.io/sampler v1.2.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
+rsc.io/sampler v1.3.0 h1:HLGR/BgEtI3r0uymSP/nl2uPLsUnNJX8toRyhfpBTII=
+rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
+rsc.io/testonly v1.0.0 h1:K/VWHdO+Jv7woUXG0GzVNx1czBXUt3Ib1deaMn+xk64=
+rsc.io/testonly v1.0.0/go.mod h1:OqmGbIFOcF+XrFReLOGZ6BhMM7uMBiQwZsyNmh74SzY=
+-- use.go --
+package use
+
+import _ "rsc.io/quote"
+-- graph.want --
+m golang.org/x/text@v0.0.0-20170915032832-14c0d48ead0c
+m rsc.io/quote@v1.5.2
+m rsc.io/sampler@v1.3.0
+m rsc.io/testonly@v1.0.0
+rsc.io/quote@v1.5.2 rsc.io/sampler@v1.3.0
+rsc.io/sampler@v1.3.0 golang.org/x/text@v0.0.0-20170915032832-14c0d48ead0c
+-- why.want --
+# rsc.io/sampler
+m
+rsc.io/quote
+rsc.io/sampler
+-- why-broken.want --
+# rsc.io/sampler
+(main module does not need module rsc.io/sampler)