[go] cmd/go: proceed with GOPATH unset if the command doesn't use it

[Bryan C. Mills (Gerrit)]

Bryan C. Mills submitted this change.

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2 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.

Approvals: Jay Conrod: Looks good to me, approved Bryan C. Mills: Trusted; Run TryBots Go Bot: TryBots succeeded

cmd/go: proceed with GOPATH unset if the command doesn't use it

For #43938

Change-Id: I0937b9bb6de3d29d7242ee61f053d4803277dc0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/351329
Trust: Bryan C. Mills <bcm...@google.com>
Run-TryBot: Bryan C. Mills <bcm...@google.com>
TryBot-Result: Go Bot <go...@golang.org>
Reviewed-by: Jay Conrod <jayc...@google.com>
---
M src/cmd/go/internal/modfetch/cache.go
M src/cmd/go/internal/modload/init.go
M src/cmd/go/testdata/script/mod_gomodcache.txt
A src/cmd/go/testdata/script/mod_no_gopath.txt
4 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/src/cmd/go/internal/modfetch/cache.go b/src/cmd/go/internal/modfetch/cache.go
index b01b467..8d299e9 100644
--- a/src/cmd/go/internal/modfetch/cache.go
+++ b/src/cmd/go/internal/modfetch/cache.go
@@ -720,7 +720,7 @@
 	if cfg.GOMODCACHE == "" {
 		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
 		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
-		return fmt.Errorf("internal error: cfg.GOMODCACHE not set")
+		return fmt.Errorf("module cache not found: neither GOMODCACHE nor GOPATH is set")
 	}
 	if !filepath.IsAbs(cfg.GOMODCACHE) {
 		return fmt.Errorf("GOMODCACHE entry is relative; must be absolute path: %q.\n", cfg.GOMODCACHE)
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index a855e6c..83414fe 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -246,6 +246,12 @@
 
 func BinDir() string {
 	Init()
+	if cfg.GOBIN != "" {
+		return cfg.GOBIN
+	}
+	if gopath == "" {
+		return ""
+	}
 	return filepath.Join(gopath, "bin")
 }
 
@@ -381,12 +387,11 @@
 		"verify, graph, and why. Implement support for go mod download and add test cases" +
 		"to ensure verify, graph, and why work properly.")
 	list := filepath.SplitList(cfg.BuildContext.GOPATH)
-	if len(list) == 0 || list[0] == "" {
-		base.Fatalf("missing $GOPATH")
-	}
-	gopath = list[0]
-	if _, err := fsys.Stat(filepath.Join(gopath, "go.mod")); err == nil {
-		base.Fatalf("$GOPATH/go.mod exists but should not")
+	if len(list) > 0 && list[0] != "" {
+		gopath = list[0]
+		if _, err := fsys.Stat(filepath.Join(gopath, "go.mod")); err == nil {
+			base.Fatalf("$GOPATH/go.mod exists but should not")
+		}
 	}
 
 	if inWorkspaceMode() {
diff --git a/src/cmd/go/testdata/script/mod_gomodcache.txt b/src/cmd/go/testdata/script/mod_gomodcache.txt
index 74a3c79..a9d7ab3 100644
--- a/src/cmd/go/testdata/script/mod_gomodcache.txt
+++ b/src/cmd/go/testdata/script/mod_gomodcache.txt
@@ -31,11 +31,18 @@
 go env GOMODCACHE
 stdout $HOME[/\\]go[/\\]pkg[/\\]mod
 
-# If GOMODCACHE isn't set and GOPATH starts with the path list separator, it's an error.
+# If GOMODCACHE isn't set and GOPATH starts with the path list separator,
+# GOMODCACHE is empty and any command that needs it errors out.
 env GOMODCACHE=
 env GOPATH=${:}$WORK/this/is/ignored
-! go env GOMODCACHE
-stderr 'missing \$GOPATH'
+
+go env GOMODCACHE
+stdout '^$'
+! stdout .
+! stderr .
+
+! go mod download rsc.io/qu...@v1.0.0
+stderr '^go: module cache not found: neither GOMODCACHE nor GOPATH is set$'
 
 # If GOMODCACHE isn't set and GOPATH has multiple elements only the first is used.
 env GOMODCACHE=
diff --git a/src/cmd/go/testdata/script/mod_no_gopath.txt b/src/cmd/go/testdata/script/mod_no_gopath.txt
new file mode 100644
index 0000000..ed91f5d
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_no_gopath.txt
@@ -0,0 +1,15 @@
+# https://golang.org/issue/43938: 'go build' should succeed
+# if GOPATH and the variables needed for its default value
+# are all unset but not relevant to the specific command.
+
+env HOME=''
+env home=''
+env GOPATH=''
+
+go list -deps main.go
+stdout '^io$'
+
+-- main.go --
+package main
+
+import _ "io"

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Gerrit-Project: go

Gerrit-Branch: master

Gerrit-Change-Id: I0937b9bb6de3d29d7242ee61f053d4803277dc0f

Gerrit-Change-Number: 351329

Gerrit-PatchSet: 4

Gerrit-Owner: Bryan C. Mills <bcm...@google.com>

Gerrit-Reviewer: Bryan C. Mills <bcm...@google.com>

Gerrit-Reviewer: Go Bot <go...@golang.org>

Gerrit-Reviewer: Jay Conrod <jayc...@google.com>

Gerrit-Reviewer: Michael Matloob <mat...@golang.org>

Gerrit-MessageType: merged