diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index 39e387b9e4b4fa..d446e457b5a14e 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -2662,7 +2662,7 @@ func TestBadCommandLines(t *testing.T) {
 	tg.tempFile("src/-x/x.go", "package x\n")
 	tg.setenv("GOPATH", tg.path("."))
 	tg.runFail("build", "--", "-x")
-	tg.grepStderr("invalid input directory name \"-x\"", "did not reject -x directory")
+	tg.grepStderr("invalid import path \"-x\"", "did not reject -x import path")
 
 	tg.tempFile("src/-x/y/y.go", "package y\n")
 	tg.setenv("GOPATH", tg.path("."))
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 21dcee1315f9e2..6aea54340d71db 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -318,16 +318,16 @@ func (p *Package) copyBuild(pp *build.Package) {
 
 // A PackageError describes an error loading information about a package.
 type PackageError struct {
-	ImportStack   []string // shortest path from package named on command line to this one
-	Pos           string   // position of error
-	Err           error    // the error itself
-	IsImportCycle bool     // the error is an import cycle
-	Hard          bool     // whether the error is soft or hard; soft errors are ignored in some places
+	ImportStack      []string // shortest path from package named on command line to this one
+	Pos              string   // position of error
+	Err              error    // the error itself
+	IsImportCycle    bool     // the error is an import cycle
+	Hard             bool     // whether the error is soft or hard; soft errors are ignored in some places
+	alwaysPrintStack bool     // whether to always print the ImportStack
 }
 
 func (p *PackageError) Error() string {
-	// Import cycles deserve special treatment.
-	if p.Pos != "" && !p.IsImportCycle {
+	if p.Pos != "" && (len(p.ImportStack) == 0 || !p.alwaysPrintStack) {
 		// Omit import stack. The full path to the file where the error
 		// is the most important thing.
 		return p.Pos + ": " + p.Err.Error()
@@ -339,15 +339,14 @@ func (p *PackageError) Error() string {
 	// last path on the stack, we don't omit the path. An error like
 	// "package A imports B: error loading C caused by B" would not be clearer
 	// if "imports B" were omitted.
-	stack := p.ImportStack
-	var ierr ImportPathError
-	if len(stack) > 0 && errors.As(p.Err, &ierr) && ierr.ImportPath() == stack[len(stack)-1] {
-		stack = stack[:len(stack)-1]
-	}
-	if len(stack) == 0 {
+	if len(p.ImportStack) == 0 {
 		return p.Err.Error()
 	}
-	return "package " + strings.Join(stack, "\n\timports ") + ": " + p.Err.Error()
+	var optpos string
+	if p.Pos != "" {
+		optpos = "\n\t" + p.Pos
+	}
+	return "package " + strings.Join(p.ImportStack, "\n\timports ") + optpos + ": " + p.Err.Error()
 }
 
 func (p *PackageError) Unwrap() error { return p.Err }
@@ -549,9 +548,6 @@ func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportS
 		panic("LoadImport called with empty package path")
 	}
 
-	stk.Push(path)
-	defer stk.Pop()
-
 	var parentPath, parentRoot string
 	parentIsStd := false
 	if parent != nil {
@@ -564,6 +560,11 @@ func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportS
 		pre.preloadImports(bp.Imports, bp)
 	}
 	if bp == nil {
+		if importErr, ok := err.(ImportPathError); !ok || importErr.ImportPath() != path {
+			// Only add path to the error's import stack if it's not already present on the error.
+			stk.Push(path)
+			defer stk.Pop()
+		}
 		return &Package{
 			PackagePublic: PackagePublic{
 				ImportPath: path,
@@ -578,7 +579,9 @@ func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportS
 	importPath := bp.ImportPath
 	p := packageCache[importPath]
 	if p != nil {
+		stk.Push(path)
 		p = reusePackage(p, stk)
+		stk.Pop()
 	} else {
 		p = new(Package)
 		p.Internal.Local = build.IsLocalImport(path)
@@ -588,8 +591,11 @@ func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportS
 		// Load package.
 		// loadPackageData may return bp != nil even if an error occurs,
 		// in order to return partial information.
-		p.load(stk, bp, err)
-		if p.Error != nil && p.Error.Pos == "" {
+		p.load(path, stk, bp, err)
+		// Add position information unless this is a NoGoError or an ImportCycle error.
+		// Import cycles deserve special treatment.
+		var g *build.NoGoError
+		if p.Error != nil && p.Error.Pos == "" && !errors.As(err, &g) && !p.Error.IsImportCycle {
 			p = setErrorPos(p, importPos)
 		}
 
@@ -608,7 +614,7 @@ func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportS
 		return setErrorPos(perr, importPos)
 	}
 	if mode&ResolveImport != 0 {
-		if perr := disallowVendor(srcDir, path, p, stk); perr != p {
+		if perr := disallowVendor(srcDir, path, parentPath, p, stk); perr != p {
 			return setErrorPos(perr, importPos)
 		}
 	}
@@ -1246,7 +1252,7 @@ func disallowInternal(srcDir string, importer *Package, importerPath string, p *
 	// as if it were generated into the testing directory tree
 	// (it's actually in a temporary directory outside any Go tree).
 	// This cleans up a former kludge in passing functionality to the testing package.
-	if strings.HasPrefix(p.ImportPath, "testing/internal") && len(*stk) >= 2 && (*stk)[len(*stk)-2] == "testmain" {
+	if str.HasPathPrefix(p.ImportPath, "testing/internal") && importerPath == "testmain" {
 		return p
 	}
 
@@ -1262,11 +1268,10 @@ func disallowInternal(srcDir string, importer *Package, importerPath string, p *
 		return p
 	}
 
-	// The stack includes p.ImportPath.
-	// If that's the only thing on the stack, we started
+	// importerPath is empty: we started
 	// with a name given on the command line, not an
 	// import. Anything listed on the command line is fine.
-	if len(*stk) == 1 {
+	if importerPath == "" {
 		return p
 	}
 
@@ -1315,8 +1320,9 @@ func disallowInternal(srcDir string, importer *Package, importerPath string, p *
 	// Internal is present, and srcDir is outside parent's tree. Not allowed.
 	perr := *p
 	perr.Error = &PackageError{
-		ImportStack: stk.Copy(),
-		Err:         ImportErrorf(p.ImportPath, "use of internal package "+p.ImportPath+" not allowed"),
+		alwaysPrintStack: true,
+		ImportStack:      stk.Copy(),
+		Err:              ImportErrorf(p.ImportPath, "use of internal package "+p.ImportPath+" not allowed"),
 	}
 	perr.Incomplete = true
 	return &perr
@@ -1344,16 +1350,15 @@ func findInternal(path string) (index int, ok bool) {
 // disallowVendor checks that srcDir is allowed to import p as path.
 // If the import is allowed, disallowVendor returns the original package p.
 // If not, it returns a new package containing just an appropriate error.
-func disallowVendor(srcDir string, path string, p *Package, stk *ImportStack) *Package {
-	// The stack includes p.ImportPath.
-	// If that's the only thing on the stack, we started
+func disallowVendor(srcDir string, path string, importerPath string, p *Package, stk *ImportStack) *Package {
+	// If the importerPath is empty, we started
 	// with a name given on the command line, not an
 	// import. Anything listed on the command line is fine.
-	if len(*stk) == 1 {
+	if importerPath == "" {
 		return p
 	}
 
-	if perr := disallowVendorVisibility(srcDir, p, stk); perr != p {
+	if perr := disallowVendorVisibility(srcDir, p, importerPath, stk); perr != p {
 		return perr
 	}
 
@@ -1376,12 +1381,12 @@ func disallowVendor(srcDir string, path string, p *Package, stk *ImportStack) *P
 // is not subject to the rules, only subdirectories of vendor.
 // This allows people to have packages and commands named vendor,
 // for maximal compatibility with existing source trees.
-func disallowVendorVisibility(srcDir string, p *Package, stk *ImportStack) *Package {
-	// The stack includes p.ImportPath.
-	// If that's the only thing on the stack, we started
+func disallowVendorVisibility(srcDir string, p *Package, importerPath string, stk *ImportStack) *Package {
+	// The stack does not include p.ImportPath.
+	// If there's nothing on the stack, we started
 	// with a name given on the command line, not an
 	// import. Anything listed on the command line is fine.
-	if len(*stk) == 1 {
+	if importerPath == "" {
 		return p
 	}
 
@@ -1525,7 +1530,8 @@ func (p *Package) DefaultExecName() string {
 
 // 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) {
+// stk contains the import stack, not including path itself.
+func (p *Package) load(path string, stk *ImportStack, bp *build.Package, err error) {
 	p.copyBuild(bp)
 
 	// The localPrefix is the path we interpret ./ imports relative to.
@@ -1548,7 +1554,16 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 
 	if err != nil {
 		p.Incomplete = true
+		// Report path in error stack unless err is an ImportPathError with path already set.
+		pushed := false
+		if e, ok := err.(ImportPathError); !ok || e.ImportPath() != path {
+			stk.Push(path)
+			pushed = true // Remember to pop after setError.
+		}
 		setError(base.ExpandScanner(p.rewordError(err)))
+		if pushed {
+			stk.Pop()
+		}
 		if _, isScanErr := err.(scanner.ErrorList); !isScanErr {
 			return
 		}
@@ -1675,6 +1690,23 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		}
 	}
 
+	// Check for case-insensitive collisions of import paths.
+	fold := str.ToFold(p.ImportPath)
+	if other := foldPath[fold]; other == "" {
+		foldPath[fold] = p.ImportPath
+	} else if other != p.ImportPath {
+		setError(ImportErrorf(p.ImportPath, "case-insensitive import collision: %q and %q", p.ImportPath, other))
+		return
+	}
+
+	if !SafeArg(p.ImportPath) {
+		setError(ImportErrorf(p.ImportPath, "invalid import path %q", p.ImportPath))
+		return
+	}
+
+	stk.Push(path)
+	defer stk.Pop()
+
 	// Check for case-insensitive collision of input files.
 	// To avoid problems on case-insensitive files, we reject any package
 	// where two different input files have equal names under a case-insensitive
@@ -1703,10 +1735,6 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		setError(fmt.Errorf("invalid input directory name %q", name))
 		return
 	}
-	if !SafeArg(p.ImportPath) {
-		setError(ImportErrorf(p.ImportPath, "invalid import path %q", p.ImportPath))
-		return
-	}
 
 	// Build list of imported packages and full dependency list.
 	imports := make([]*Package, 0, len(p.Imports))
@@ -1770,15 +1798,6 @@ func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 		return
 	}
 
-	// Check for case-insensitive collisions of import paths.
-	fold := str.ToFold(p.ImportPath)
-	if other := foldPath[fold]; other == "" {
-		foldPath[fold] = p.ImportPath
-	} else if other != p.ImportPath {
-		setError(ImportErrorf(p.ImportPath, "case-insensitive import collision: %q and %q", p.ImportPath, other))
-		return
-	}
-
 	if cfg.ModulesEnabled && p.Error == nil {
 		mainPath := p.ImportPath
 		if p.Internal.CmdlineFiles {
@@ -2266,9 +2285,7 @@ func GoFilesPackage(gofiles []string) *Package {
 	pkg := new(Package)
 	pkg.Internal.Local = true
 	pkg.Internal.CmdlineFiles = true
-	stk.Push("main")
-	pkg.load(&stk, bp, err)
-	stk.Pop()
+	pkg.load("command-line-arguments", &stk, bp, err)
 	pkg.Internal.LocalPrefix = dirToImportPath(dir)
 	pkg.ImportPath = "command-line-arguments"
 	pkg.Target = ""
diff --git a/src/cmd/go/internal/load/test.go b/src/cmd/go/internal/load/test.go
index 866e0e567f2b8b..6465f46f4ec5da 100644
--- a/src/cmd/go/internal/load/test.go
+++ b/src/cmd/go/internal/load/test.go
@@ -56,7 +56,6 @@ func TestPackagesFor(p *Package, cover *TestCover) (pmain, ptest, pxtest *Packag
 		}
 		if len(p1.DepsErrors) > 0 {
 			perr := p1.DepsErrors[0]
-			perr.Pos = "" // show full import stack
 			err = perr
 			break
 		}
diff --git a/src/cmd/go/testdata/script/mod_empty_err.txt b/src/cmd/go/testdata/script/mod_empty_err.txt
index b309f634dd349d..982e6b2e518d96 100644
--- a/src/cmd/go/testdata/script/mod_empty_err.txt
+++ b/src/cmd/go/testdata/script/mod_empty_err.txt
@@ -10,7 +10,7 @@ go list -e -f {{.Error}} ./empty
 stdout 'no Go files in \$WORK[/\\]empty'
 
 go list -e -f {{.Error}} ./exclude
-stdout 'package example.com/m/exclude: build constraints exclude all Go files in \$WORK[/\\]exclude'
+stdout 'build constraints exclude all Go files in \$WORK[/\\]exclude'
 
 go list -e -f {{.Error}} ./missing
 stdout 'stat '$WORK'[/\\]missing: directory not found'
diff --git a/src/cmd/go/testdata/script/test_import_error_stack.txt b/src/cmd/go/testdata/script/test_import_error_stack.txt
index 3b796053f7cfd1..c66c1213a428c0 100644
--- a/src/cmd/go/testdata/script/test_import_error_stack.txt
+++ b/src/cmd/go/testdata/script/test_import_error_stack.txt
@@ -1,6 +1,9 @@
 ! go test testdep/p1
 stderr 'package testdep/p1 \(test\)\n\timports testdep/p2\n\timports testdep/p3: build constraints exclude all Go files ' # check for full import stack
 
+! go vet testdep/p1
+stderr 'package testdep/p1 \(test\)\n\timports testdep/p2\n\timports testdep/p3: build constraints exclude all Go files ' # check for full import stack
+
 -- testdep/p1/p1.go --
 package p1
 -- testdep/p1/p1_test.go --
diff --git a/src/cmd/go/testdata/script/vet_internal.txt b/src/cmd/go/testdata/script/vet_internal.txt
index 46e1ac7398d894..85f709302c8935 100644
--- a/src/cmd/go/testdata/script/vet_internal.txt
+++ b/src/cmd/go/testdata/script/vet_internal.txt
@@ -3,28 +3,28 @@ env GO111MODULE=off
 # Issue 36173. Verify that "go vet" prints line numbers on load errors.
 
 ! go vet a/a.go
-stderr '^a[/\\]a.go:5:3: use of internal package'
+stderr '^package command-line-arguments\n\ta[/\\]a.go:5:3: use of internal package'
 
 ! go vet a/a_test.go
-stderr '^package command-line-arguments \(test\): use of internal package' # BUG
+stderr '^package command-line-arguments \(test\)\n\ta[/\\]a_test.go:4:3: use of internal package'
 
 ! go vet a
-stderr '^a[/\\]a.go:5:3: use of internal package'
+stderr '^package a\n\ta[/\\]a.go:5:3: use of internal package'
 
 go vet b/b.go
 ! stderr 'use of internal package'
 
 ! go vet b/b_test.go
-stderr '^package command-line-arguments \(test\): use of internal package' # BUG
+stderr '^package command-line-arguments \(test\)\n\tb[/\\]b_test.go:4:3: use of internal package'
 
 ! go vet depends-on-a/depends-on-a.go
-stderr '^a[/\\]a.go:5:3: use of internal package'
+stderr '^package command-line-arguments\n\timports a\n\ta[/\\]a.go:5:3: use of internal package'
 
 ! go vet depends-on-a/depends-on-a_test.go
-stderr '^package command-line-arguments \(test\)\n\timports a: use of internal package a/x/internal/y not allowed$' # BUG
+stderr '^package command-line-arguments \(test\)\n\timports a\n\ta[/\\]a.go:5:3: use of internal package a/x/internal/y not allowed'
 
 ! go vet depends-on-a
-stderr '^a[/\\]a.go:5:3: use of internal package'
+stderr '^package depends-on-a\n\timports a\n\ta[/\\]a.go:5:3: use of internal package'
 
 -- a/a.go --
 // A package with bad imports in both src and test