cmd/go: show an error when a package in a module conflicts with one i…

…n std

Fixes #35270

Change-Id: I5d2a04359702be6dc04affb867540091b926bc23
Reviewed-on: https://go-review.googlesource.com/c/go/+/434095
Run-TryBot: xie cui <523516579@qq.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/go/internal/modload/import.go

@@ -286,6 +286,10 @@ func importFromModules(ctx context.Context, path string, rs *Requirements, mg *M
 		return module.Version{}, "", "", nil, &invalidImportError{importPath: path, err: err}
 	}
 
+	// Check each module on the build list.
+	var dirs, roots []string
+	var mods []module.Version
+
 	// Is the package in the standard library?
 	pathIsStd := search.IsStandardImportPath(path)
 	if pathIsStd && modindex.IsStandardPackage(cfg.GOROOT, cfg.BuildContext.Compiler, path) {
@@ -303,35 +307,43 @@ func importFromModules(ctx context.Context, path string, rs *Requirements, mg *M
 		if str.HasPathPrefix(path, "cmd") {
 			modroot = filepath.Join(cfg.GOROOTsrc, "cmd")
 		}
-		return module.Version{}, modroot, dir, nil, nil
+		dirs = append(dirs, dir)
+		roots = append(roots, modroot)
+		mods = append(mods, module.Version{})
 	}
-
 	// -mod=vendor is special.
 	// Everything must be in the main module or the main module's vendor directory.
 	if cfg.BuildMod == "vendor" {
 		mainModule := MainModules.mustGetSingleMainModule()
 		modRoot := MainModules.ModRoot(mainModule)
 		mainDir, mainOK, mainErr := dirInModule(path, MainModules.PathPrefix(mainModule), modRoot, true)
+		if mainOK {
+			mods = append(mods, mainModule)
+			dirs = append(dirs, mainDir)
+			roots = append(roots, modRoot)
+		}
 		vendorDir, vendorOK, _ := dirInModule(path, "", filepath.Join(modRoot, "vendor"), false)
-		if mainOK && vendorOK {
-			return module.Version{}, modRoot, "", nil, &AmbiguousImportError{importPath: path, Dirs: []string{mainDir, vendorDir}}
+		if vendorOK {
+			readVendorList(mainModule)
+			mods = append(mods, vendorPkgModule[path])
+			dirs = append(dirs, vendorDir)
+			roots = append(roots, modRoot)
 		}
-		// Prefer to return main directory if there is one,
-		// Note that we're not checking that the package exists.
-		// We'll leave that for load.
-		if !vendorOK && mainDir != "" {
-			return mainModule, modRoot, mainDir, nil, nil
+
+		if len(dirs) > 1 {
+			return module.Version{}, modRoot, "", nil, &AmbiguousImportError{importPath: path, Dirs: dirs}
 		}
+
 		if mainErr != nil {
 			return module.Version{}, "", "", nil, mainErr
 		}
-		readVendorList(mainModule)
-		return vendorPkgModule[path], modRoot, vendorDir, nil, nil
-	}
 
-	// Check each module on the build list.
-	var dirs, roots []string
-	var mods []module.Version
+		if len(dirs) == 0 {
+			return module.Version{}, modRoot, "", nil, &ImportMissingError{Path: path}
+		}
+
+		return mods[0], roots[0], dirs[0], nil, nil
+	}
 
 	// Iterate over possible modules for the path, not all selected modules.
 	// Iterating over selected modules would make the overall loading time

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

@@ -27,7 +27,8 @@ cmp go.mod go.mod.orig
 
 ! go list -mod=vendor all
 ! stderr '^go: inconsistent vendoring'
-stderr 'cannot find package "." in:\n\t.*[/\\]vendor[/\\]example.com[/\\]badedit$'
+stderr 'go: finding module for package example.com/badedit'
+stderr 'cannot query module due to -mod=vendor'
 
 # When we set -mod=mod, the go version should be updated immediately,
 # to the current version, converting the requirements from eager to lazy.

src/cmd/go/testdata/script/mod_issue35270.txt

@@ -0,0 +1,57 @@
+
+cd a
+! go build
+stderr '^ambiguous import: found package image in multiple modules:\s+image\s+.+\s.+image.+\s$'
+
+
+cd ../b
+! go build -mod=vendor
+stderr '^main.go:4:5: ambiguous import: found package image in multiple directories:\s+.+image\s+.+image\s+$'
+
+cd ../c
+! go build -mod=vendor
+stderr 'main.go:4:5: package p is not in GOROOT'
+
+-- a/go.mod --
+module image
+
+-- a/main.go --
+package main
+
+func main() {
+    println("hello world!")
+}
+
+-- b/go.mod --
+module test
+
+-- b/vendor/image/b.go --
+package image
+func Add(a, b int) int {
+    return a + b
+}
+
+-- b/main.go --
+package main
+
+import (
+    "image"
+)
+
+func main() {
+    println(image.Add(1,1))
+}
+
+-- c/go.mod --
+module test
+
+-- c/main.go --
+package main
+
+import (
+    "p"
+)
+
+func main() {
+    println(p.Add(1,1))
+}

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

@@ -22,8 +22,9 @@ cd broken
 ! go build -mod=readonly
 stderr 'disabled by -mod=readonly'
 ! go build -mod=vendor
-stderr 'cannot find package'
-stderr 'hpack'
+stderr 'go: finding module for package golang.org/x/net/http2/hpack'
+stderr 'http.go:5:2: cannot query module due to -mod=vendor'
+
 
 # ...even if they explicitly use the "cmd/vendor/" or "vendor/" prefix.
 cd ../importcmd

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

@@ -55,7 +55,7 @@ stderr 'go: module diamondright: can''t resolve module using the vendor director
 go list -mod=mod -f {{.Dir}} w
 stdout 'src[\\/]w'
 ! go list -mod=vendor -f {{.Dir}} w
-stderr 'src[\\/]vendor[\\/]w'
+stderr 'package w is not in GOROOT'
 
 go list -mod=mod -f {{.Dir}} diamondright
 stdout 'src[\\/]diamondright'