cmd/go: report implicit cgo inputs in go list -compiled

Tools using go list -compiled expect to see an Imports list
that includes all the imports in CompiledGoFiles.
Make sure the list includes the cgo-generated imports.

Fixes #26136.

Change-Id: I6cfe14063f8edfe65a7af37522c7551272115b82
Reviewed-on: https://go-review.googlesource.com/128935
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/list/list.go

@@ -20,6 +20,7 @@ import (
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/load"
 	"cmd/go/internal/modload"
+	"cmd/go/internal/str"
 	"cmd/go/internal/work"
 )
 
@@ -146,7 +147,8 @@ instead of using the template format.
 The -compiled flag causes list to set CompiledGoFiles to the Go source
 files presented to the compiler. Typically this means that it repeats
 the files listed in GoFiles and then also adds the Go code generated
-by processing CgoFiles and SwigFiles.
+by processing CgoFiles and SwigFiles. The Imports list contains the
+union of all imports from both GoFiles and CompiledGoFiles.
 
 The -deps flag causes list to iterate over not just the named packages
 but also all their dependencies. It visits them in a depth-first post-order
@@ -517,6 +519,10 @@ func runList(cmd *base.Command, args []string) {
 		p.TestImports = p.Resolve(p.TestImports)
 		p.XTestImports = p.Resolve(p.XTestImports)
 		p.DepOnly = !cmdline[p]
+
+		if *listCompiled {
+			p.Imports = str.StringList(p.Imports, p.Internal.CompiledImports)
+		}
 	}
 
 	if *listTest {

src/cmd/go/internal/load/pkg.go

@@ -157,6 +157,7 @@ type PackageInternal struct {
 	// Unexported fields are not part of the public API.
 	Build             *build.Package
 	Imports           []*Package           // this package's direct imports
+	CompiledImports   []string             // additional Imports necessary when using CompiledGoFiles (all from standard library)
 	RawImports        []string             // this package's original imports as they appear in the text of the program
 	ForceLibrary      bool                 // this package is a library (even if named "main")
 	CmdlineFiles      bool                 // package built from files listed on command line
@@ -1327,31 +1328,37 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	// Build augmented import list to add implicit dependencies.
 	// Be careful not to add imports twice, just to avoid confusion.
 	importPaths := p.Imports
-	addImport := func(path string) {
+	addImport := func(path string, forCompiler bool) {
 		for _, p := range importPaths {
 			if path == p {
 				return
 			}
 		}
 		importPaths = append(importPaths, path)
+		if forCompiler {
+			p.Internal.CompiledImports = append(p.Internal.CompiledImports, path)
+		}
 	}
 
-	// Cgo translation adds imports of "runtime/cgo" and "syscall",
+	// Cgo translation adds imports of "unsafe", "runtime/cgo" and "syscall",
 	// except for certain packages, to avoid circular dependencies.
+	if p.UsesCgo() {
+		addImport("unsafe", true)
+	}
 	if p.UsesCgo() && (!p.Standard || !cgoExclude[p.ImportPath]) && cfg.BuildContext.Compiler != "gccgo" {
-		addImport("runtime/cgo")
+		addImport("runtime/cgo", true)
 	}
 	if p.UsesCgo() && (!p.Standard || !cgoSyscallExclude[p.ImportPath]) {
-		addImport("syscall")
+		addImport("syscall", true)
 	}
 
 	// SWIG adds imports of some standard packages.
 	if p.UsesSwig() {
 		if cfg.BuildContext.Compiler != "gccgo" {
-			addImport("runtime/cgo")
+			addImport("runtime/cgo", true)
 		}
-		addImport("syscall")
+		addImport("syscall", true)
-		addImport("sync")
+		addImport("sync", true)
 
 		// TODO: The .swig and .swigcxx files can use
 		// %go_import directives to import other packages.
@@ -1360,7 +1367,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	// The linker loads implicit dependencies.
 	if p.Name == "main" && !p.Internal.ForceLibrary {
 		for _, dep := range LinkerDeps(p) {
-			addImport(dep)
+			addImport(dep, false)
 		}
 	}
 

src/cmd/go/testdata/script/list_compiled_imports.txt

@@ -0,0 +1,29 @@
+[!cgo] skip
+
+# go list should report import "C"
+cd x
+go list -f '{{.Imports}}'
+! stdout runtime/cgo
+! stdout unsafe
+! stdout syscall
+stdout C
+stdout unicode
+stdout unicode/utf16
+
+# go list -compiled should report imports in compiled files as well,
+# adding "runtime/cgo", "unsafe", and "syscall" but not dropping "C".
+go list -compiled -f '{{.Imports}}'
+stdout runtime/cgo
+stdout unsafe
+stdout syscall
+stdout C
+stdout unicode
+stdout unicode/utf16
+
+-- x/x.go --
+package x
+import "C"
+import "unicode" // does not use unsafe, syscall, runtime/cgo, unicode/utf16
+-- x/x1.go --
+package x
+import "unicode/utf16" // does not use unsafe, syscall, runtime/cgo, unicode