cmd/go: import runtime/cgo when externally linking

Fixes #31544

Change-Id: Ic99875ad227876eb741e93653589310327c9c0ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/477195
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

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

@@ -684,6 +684,15 @@ const (
 	// GetTestDeps is for download (part of "go get") and indicates
 	// that test dependencies should be fetched too.
 	GetTestDeps
+
+	// The remainder are internal modes for calls to loadImport.
+
+	// cmdlinePkg is for a package mentioned on the command line.
+	cmdlinePkg
+
+	// cmdlinePkgLiteral is for a package mentioned on the command line
+	// without using any wildcards or meta-patterns.
+	cmdlinePkgLiteral
 )
 
 // LoadImport scans the directory named by path, which must be an import path,
@@ -738,18 +747,30 @@ func loadImport(ctx context.Context, opts PackageOpts, pre *preload, path, srcDi
 		return p
 	}
 
+	setCmdline := func(p *Package) {
+		if mode&cmdlinePkg != 0 {
+			p.Internal.CmdlinePkg = true
+		}
+		if mode&cmdlinePkgLiteral != 0 {
+			p.Internal.CmdlinePkgLiteral = true
+		}
+	}
+
 	importPath := bp.ImportPath
 	p := packageCache[importPath]
 	if p != nil {
 		stk.Push(path)
 		p = reusePackage(p, stk)
 		stk.Pop()
+		setCmdline(p)
 	} else {
 		p = new(Package)
 		p.Internal.Local = build.IsLocalImport(path)
 		p.ImportPath = importPath
 		packageCache[importPath] = p
 
+		setCmdline(p)
+
 		// Load package.
 		// loadPackageData may return bp != nil even if an error occurs,
 		// in order to return partial information.
@@ -2849,15 +2870,15 @@ func PackagesAndErrors(ctx context.Context, opts PackageOpts, patterns []string)
 			if pkg == "" {
 				panic(fmt.Sprintf("ImportPaths returned empty package for pattern %s", m.Pattern()))
 			}
-			p := loadImport(ctx, opts, pre, pkg, base.Cwd(), nil, &stk, nil, 0)
-			p.Match = append(p.Match, m.Pattern())
-			p.Internal.CmdlinePkg = true
+			mode := cmdlinePkg
 			if m.IsLiteral() {
 				// Note: do not set = m.IsLiteral unconditionally
 				// because maybe we'll see p matching both
 				// a literal and also a non-literal pattern.
-				p.Internal.CmdlinePkgLiteral = true
+				mode |= cmdlinePkgLiteral
 			}
+			p := loadImport(ctx, opts, pre, pkg, base.Cwd(), nil, &stk, nil, mode)
+			p.Match = append(p.Match, m.Pattern())
 			if seenPkg[p] {
 				continue
 			}

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

@@ -0,0 +1,38 @@
+# This test requires external linking. Assume that if cgo is supported
+# then external linking works.
+[!cgo] skip 'links and runs binaries'
+
+# Only run on Unix systems that support -static.
+[GOOS:windows] skip
+[GOOS:plan9] skip
+
+# Ordinary build should work.
+go build
+exec ./hello
+stdout Hello
+
+# Building with -linkmode=external should not say anything about
+# runtime/cgo (issue #31544).
+go build -ldflags=-linkmode=external
+! stderr runtime/cgo
+exec ./hello
+stdout Hello
+
+# Building with -linkmode=external -extldflags=-static should work.
+go build -ldflags='-linkmode=external -extldflags=-static'
+! stderr runtime/cgo
+exec ./hello
+stdout Hello
+
+-- go.mod --
+module hello
+
+go 1.20
+-- hello.go --
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello, world")
+}