cmd/go: set expected filename when building a local package with -o is pointing to a folder

In the local package build process, when -o is pointing to an existing folder, the object
the filename is generated from files listed on the command line like when the -o is
not pointing to a folder instead of using the `importPath` that is going to be `command-line-arguments`

Fixes #34535

Change-Id: I09a7609c17a2ccdd83da32f01247c0ef473dea1e
GitHub-Last-Rev: b3224226a3
GitHub-Pull-Request: golang/go#34562
Reviewed-on: https://go-review.googlesource.com/c/go/+/197544
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

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

@@ -1391,26 +1391,51 @@ var cgoSyscallExclude = map[string]bool{
 
 var foldPath = make(map[string]string)
 
-// DefaultExecName returns the default executable name
-// for a package with the import path importPath.
+// exeFromImportPath returns an executable name
+// for a package using the import path.
 //
-// The default executable name is the last element of the import path.
+// The executable name is the last element of the import path.
 // In module-aware mode, an additional rule is used on import paths
 // consisting of two or more path elements. If the last element is
 // a vN path element specifying the major version, then the
 // second last element of the import path is used instead.
-func DefaultExecName(importPath string) string {
-	_, elem := pathpkg.Split(importPath)
+func (p *Package) exeFromImportPath() string {
+	_, elem := pathpkg.Split(p.ImportPath)
 	if cfg.ModulesEnabled {
 		// If this is example.com/mycmd/v2, it's more useful to
 		// install it as mycmd than as v2. See golang.org/issue/24667.
-		if elem != importPath && isVersionElement(elem) {
-			_, elem = pathpkg.Split(pathpkg.Dir(importPath))
+		if elem != p.ImportPath && isVersionElement(elem) {
+			_, elem = pathpkg.Split(pathpkg.Dir(p.ImportPath))
 		}
 	}
 	return elem
 }
 
+// exeFromFiles returns an executable name for a package
+// using the first element in GoFiles or CgoFiles collections without the prefix.
+//
+// Returns empty string in case of empty collection.
+func (p *Package) exeFromFiles() string {
+	var src string
+	if len(p.GoFiles) > 0 {
+		src = p.GoFiles[0]
+	} else if len(p.CgoFiles) > 0 {
+		src = p.CgoFiles[0]
+	} else {
+		return ""
+	}
+	_, elem := filepath.Split(src)
+	return elem[:len(elem)-len(".go")]
+}
+
+// DefaultExecName returns the default executable name for a package
+func (p *Package) DefaultExecName() string {
+	if p.Internal.CmdlineFiles {
+		return p.exeFromFiles()
+	}
+	return p.exeFromImportPath()
+}
+
 // load populates p using information from bp, err, which should
 // be the result of calling build.Context.Import.
 func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
@@ -1451,7 +1476,7 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 			p.Error = &PackageError{Err: e}
 			return
 		}
-		elem := DefaultExecName(p.ImportPath)
+		elem := p.DefaultExecName()
 		full := cfg.BuildContext.GOOS + "_" + cfg.BuildContext.GOARCH + "/" + elem
 		if cfg.BuildContext.GOOS != base.ToolGOOS || cfg.BuildContext.GOARCH != base.ToolGOARCH {
 			// Install cross-compiled binaries to subdirectories of bin.
@@ -2140,11 +2165,8 @@ func GoFilesPackage(gofiles []string) *Package {
 	pkg.Match = gofiles
 
 	if pkg.Name == "main" {
-		_, elem := filepath.Split(gofiles[0])
-		exe := elem[:len(elem)-len(".go")] + cfg.ExeSuffix
-		if cfg.BuildO == "" {
-			cfg.BuildO = exe
-		}
+		exe := pkg.DefaultExecName() + cfg.ExeSuffix
+
 		if cfg.GOBIN != "" {
 			pkg.Target = filepath.Join(cfg.GOBIN, exe)
 		} else if cfg.ModulesEnabled {

src/cmd/go/internal/load/pkg_test.go

@@ -5,39 +5,49 @@ import (
 	"testing"
 )
 
-func TestDefaultExecName(t *testing.T) {
+func TestPkgDefaultExecName(t *testing.T) {
 	oldModulesEnabled := cfg.ModulesEnabled
 	defer func() { cfg.ModulesEnabled = oldModulesEnabled }()
 	for _, tt := range []struct {
 		in         string
+		files      []string
 		wantMod    string
 		wantGopath string
 	}{
-		{"example.com/mycmd", "mycmd", "mycmd"},
-		{"example.com/mycmd/v0", "v0", "v0"},
-		{"example.com/mycmd/v1", "v1", "v1"},
-		{"example.com/mycmd/v2", "mycmd", "v2"}, // Semantic import versioning, use second last element in module mode.
-		{"example.com/mycmd/v3", "mycmd", "v3"}, // Semantic import versioning, use second last element in module mode.
-		{"mycmd", "mycmd", "mycmd"},
-		{"mycmd/v0", "v0", "v0"},
-		{"mycmd/v1", "v1", "v1"},
-		{"mycmd/v2", "mycmd", "v2"}, // Semantic import versioning, use second last element in module mode.
-		{"v0", "v0", "v0"},
-		{"v1", "v1", "v1"},
-		{"v2", "v2", "v2"},
+		{"example.com/mycmd", []string{}, "mycmd", "mycmd"},
+		{"example.com/mycmd/v0", []string{}, "v0", "v0"},
+		{"example.com/mycmd/v1", []string{}, "v1", "v1"},
+		{"example.com/mycmd/v2", []string{}, "mycmd", "v2"}, // Semantic import versioning, use second last element in module mode.
+		{"example.com/mycmd/v3", []string{}, "mycmd", "v3"}, // Semantic import versioning, use second last element in module mode.
+		{"mycmd", []string{}, "mycmd", "mycmd"},
+		{"mycmd/v0", []string{}, "v0", "v0"},
+		{"mycmd/v1", []string{}, "v1", "v1"},
+		{"mycmd/v2", []string{}, "mycmd", "v2"}, // Semantic import versioning, use second last element in module mode.
+		{"v0", []string{}, "v0", "v0"},
+		{"v1", []string{}, "v1", "v1"},
+		{"v2", []string{}, "v2", "v2"},
+		{"command-line-arguments", []string{"output.go", "foo.go"}, "output", "output"},
 	} {
 		{
 			cfg.ModulesEnabled = true
-			gotMod := DefaultExecName(tt.in)
+			pkg := new(Package)
+			pkg.ImportPath = tt.in
+			pkg.GoFiles = tt.files
+			pkg.Internal.CmdlineFiles = len(tt.files) > 0
+			gotMod := pkg.DefaultExecName()
 			if gotMod != tt.wantMod {
-				t.Errorf("DefaultExecName(%q) in module mode = %v; want %v", tt.in, gotMod, tt.wantMod)
+				t.Errorf("pkg.DefaultExecName with ImportPath = %q in module mode = %v; want %v", tt.in, gotMod, tt.wantMod)
 			}
 		}
 		{
 			cfg.ModulesEnabled = false
-			gotGopath := DefaultExecName(tt.in)
+			pkg := new(Package)
+			pkg.ImportPath = tt.in
+			pkg.GoFiles = tt.files
+			pkg.Internal.CmdlineFiles = len(tt.files) > 0
+			gotGopath := pkg.DefaultExecName()
 			if gotGopath != tt.wantGopath {
-				t.Errorf("DefaultExecName(%q) in gopath mode = %v; want %v", tt.in, gotGopath, tt.wantGopath)
+				t.Errorf("pkg.DefaultExecName with ImportPath = %q in gopath mode = %v; want %v", tt.in, gotGopath, tt.wantGopath)
 			}
 		}
 	}

src/cmd/go/internal/test/test.go

@@ -829,7 +829,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 	if p.ImportPath == "command-line-arguments" {
 		elem = p.Name
 	} else {
-		elem = load.DefaultExecName(p.ImportPath)
+		elem = p.DefaultExecName()
 	}
 	testBinary := elem + ".test"
 

src/cmd/go/internal/work/build.go

@@ -329,7 +329,7 @@ func runBuild(cmd *base.Command, args []string) {
 	explicitO := len(cfg.BuildO) > 0
 
 	if len(pkgs) == 1 && pkgs[0].Name == "main" && cfg.BuildO == "" {
-		cfg.BuildO = load.DefaultExecName(pkgs[0].ImportPath)
+		cfg.BuildO = pkgs[0].DefaultExecName()
 		cfg.BuildO += cfg.ExeSuffix
 	}
 
@@ -373,7 +373,8 @@ func runBuild(cmd *base.Command, args []string) {
 				if p.Name != "main" {
 					continue
 				}
-				p.Target = filepath.Join(cfg.BuildO, load.DefaultExecName(p.ImportPath))
+
+				p.Target = filepath.Join(cfg.BuildO, p.DefaultExecName())
 				p.Target += cfg.ExeSuffix
 				p.Stale = true
 				p.StaleReason = "build -o flag in use"
@@ -595,7 +596,7 @@ func InstallPackages(patterns []string, pkgs []*load.Package) {
 	if len(patterns) == 0 && len(pkgs) == 1 && pkgs[0].Name == "main" {
 		// Compute file 'go build' would have created.
 		// If it exists and is an executable file, remove it.
-		targ := load.DefaultExecName(pkgs[0].ImportPath)
+		targ := pkgs[0].DefaultExecName()
 		targ += cfg.ExeSuffix
 		if filepath.Join(pkgs[0].Dir, targ) != pkgs[0].Target { // maybe $GOBIN is the current directory
 			fi, err := os.Stat(targ)

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

@@ -10,6 +10,11 @@ stderr 'no main packages'
 ! go build ./cmd/c1
 stderr 'already exists and is a directory'
 
+# Verify build -o output correctly local packages
+mkdir $WORK/local
+go build -o $WORK/local ./exec.go
+exists $WORK/local/exec$GOEXE
+
 -- go.mod --
 module exmod
 
@@ -29,5 +34,10 @@ package pkg1
 -- pkg2/pkg2.go --
 package pkg2
 
+-- exec.go --
+package main
+
+func main() {}
+
 -- c1$GOEXE/keep.txt --
 Create c1 directory.