[dev.cmdgo] don't give command-line-arguments a module

Don't associate command-line-arguments with a module. Even though the
sources in the command-line-arguments package may exist within the
module's packages, the command-line-arguments package is distinct from
the package in the module. It has its own identity, and further, even if
all the same sources are listed, build tag filtering is not applied for
command-line-arguments.

For #45713

Change-Id: I555752021d58ea25e65699b4959f787ea5fa2cda
Reviewed-on: https://go-review.googlesource.com/c/go/+/339170
Trust: Michael Matloob <matloob@golang.org>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

5 files changed, 65 insertions, 35 deletions

diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index 3f2160d52d..73b51c117a 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -341,15 +341,14 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 // for modules providing packages named by path and deps. path and deps must
 // name packages that were resolved successfully with LoadPackages.
 func PackageBuildInfo(path string, deps []string) string {
-	if isStandardImportPath(path) || !Enabled() {
+	if !Enabled() {
 		return ""
 	}
-
-	target := mustFindModule(loaded, path, path)
+	target, _ := findModule(loaded, path)
 	mdeps := make(map[module.Version]bool)
 	for _, dep := range deps {
-		if !isStandardImportPath(dep) {
-			mdeps[mustFindModule(loaded, path, dep)] = true
+		if m, ok := findModule(loaded, dep); ok {
+			mdeps[m] = true
 		}
 	}
 	var mods []module.Version
@@ -375,7 +374,9 @@ func PackageBuildInfo(path string, deps []string) string {
 		}
 	}
 
-	writeEntry("mod", target)
+	if target.Path != "" {
+		writeEntry("mod", target)
+	}
 	for _, mod := range mods {
 		writeEntry("dep", mod)
 	}
@@ -383,29 +384,6 @@ func PackageBuildInfo(path string, deps []string) string {
 	return buf.String()
 }
 
-// mustFindModule is like findModule, but it calls base.Fatalf if the
-// module can't be found.
-//
-// TODO(jayconrod): remove this. Callers should use findModule and return
-// errors instead of relying on base.Fatalf.
-func mustFindModule(ld *loader, target, path string) module.Version {
-	pkg, ok := ld.pkgCache.Get(path).(*loadPkg)
-	if ok {
-		if pkg.err != nil {
-			base.Fatalf("build %v: cannot load %v: %v", target, path, pkg.err)
-		}
-		return pkg.mod
-	}
-
-	if path == "command-line-arguments" {
-		_ = TODOWorkspaces("support multiple main modules; search by modroot")
-		return MainModules.mustGetSingleMainModule()
-	}
-
-	base.Fatalf("build %v: cannot find module for path %v", target, path)
-	panic("unreachable")
-}
-
 // findModule searches for the module that contains the package at path.
 // If the package was loaded, its containing module and true are returned.
 // Otherwise, module.Version{} and false are returned.
@@ -413,10 +391,6 @@ func findModule(ld *loader, path string) (module.Version, bool) {
 	if pkg, ok := ld.pkgCache.Get(path).(*loadPkg); ok {
 		return pkg.mod, pkg.mod != module.Version{}
 	}
-	if path == "command-line-arguments" {
-		_ = TODOWorkspaces("support multiple main modules; search by modroot")
-		return MainModules.mustGetSingleMainModule(), true
-	}
 	return module.Version{}, false
 }
 
diff --git a/src/cmd/go/testdata/script/mod_list_command_line_arguments.txt b/src/cmd/go/testdata/script/mod_list_command_line_arguments.txt
new file mode 100644
index 0000000000..fd99ae84b2
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_list_command_line_arguments.txt
@@ -0,0 +1,35 @@
+# The command-line-arguments package does not belong to a module...
+cd a
+go list -f '{{.Module}}' ../b/b.go
+stdout '^<nil>$'
+
+# ... even if the arguments are sources from that module
+go list -f '{{.Module}}' a.go
+stdout '^<nil>$'
+
+[short] skip
+
+# check that the version of command-line-arguments doesn't include a module
+go build -o a.exe a.go
+go version -m a.exe
+stdout '^\tpath\tcommand-line-arguments$'
+stdout '^\tdep\ta\t\(devel\)\t$'
+! stdout mod
+
+-- a/go.mod --
+module a
+go 1.17
+-- a/a.go --
+package main
+
+import "a/dep"
+
+func main() {
+    dep.D()
+}
+-- a/dep/dep.go --
+package dep
+
+func D() {}
+-- b/b.go --
+package b
\ No newline at end of file
diff --git a/src/cmd/go/testdata/script/mod_outside.txt b/src/cmd/go/testdata/script/mod_outside.txt
index 33341f7d4b..3b4559405a 100644
--- a/src/cmd/go/testdata/script/mod_outside.txt
+++ b/src/cmd/go/testdata/script/mod_outside.txt
@@ -251,7 +251,7 @@ stdout 'using example.com/version v1.0.1'
 # outside std.
 go run ./stdonly/stdonly.go
 stdout 'path is command-line-arguments$'
-stdout 'main is command-line-arguments \(devel\)'
+stdout 'main is  $'
 
 # 'go generate' should work with file arguments.
 [exec:touch] go generate ./needmod/needmod.go
diff --git a/src/cmd/go/testdata/script/version.txt b/src/cmd/go/testdata/script/version.txt
index 8615a4aac5..f3aa57e8c7 100644
--- a/src/cmd/go/testdata/script/version.txt
+++ b/src/cmd/go/testdata/script/version.txt
@@ -28,6 +28,13 @@ go version -m fortune.exe
 stdout '^\tpath\trsc.io/fortune'
 stdout '^\tmod\trsc.io/fortune\tv1.0.0'
 
+# Check the build info of a binary built from $GOROOT/src/cmd
+go build -o test2json.exe cmd/test2json
+go version -m test2json.exe
+stdout '^test2json.exe: .+'
+stdout '^\tpath\tcmd/test2json$'
+! stdout 'mod'
+
 # Repeat the test with -buildmode=pie.
 [!buildmode:pie] stop
 go build -buildmode=pie -o external.exe rsc.io/fortune
diff --git a/src/cmd/go/testdata/script/work.txt b/src/cmd/go/testdata/script/work.txt
index 9be0958579..095d6ff174 100644
--- a/src/cmd/go/testdata/script/work.txt
+++ b/src/cmd/go/testdata/script/work.txt
@@ -42,6 +42,13 @@ go run example.com/d
 cp go.work.backwards go.work
 go run example.com/d
 
+# Test that command-line-arguments work inside and outside modules.
+# This exercises the code that determines which module command-line-arguments
+# belongs to.
+go list ./b/main.go
+go build -n -workfile=off -o foo foo.go
+go build -n -o foo foo.go
+
 -- go.work.dup --
 go 1.17
 
@@ -123,4 +130,11 @@ directory (
     d
     b
     a
-)
\ No newline at end of file
+)
+
+-- foo.go --
+package main
+import "fmt"
+func main() {
+	fmt.Println("Hello, World")
+}