From 93c17dc7c2f10e965a365e4ae6bd3b22facd2cf1 Mon Sep 17 00:00:00 2001
From: Qi Xiao <xiaqqaix@gmail.com>
Date: Tue, 22 Oct 2019 22:49:32 +0100
Subject: [PATCH] Improve handling of namespaces.

* The training colons of namespaces are now considered part of the namespace,
  simplifying the internal API.

* Added tests for more complex patterns of nested namespaces that used to fail.
---
 cliedit/highlight_deps.go                 |  29 +++---
 edit/completion/complete_command.go       |  11 ++-
 edit/completion/complete_variable.go      |  23 ++---
 edit/completion/complete_variable_test.go |  33 +++----
 edit/edcore/highlight.go                  |   7 +-
 eval/builtin_fn_misc.go                   |   6 +-
 eval/builtin_special.go                   |  26 ++---
 eval/builtin_special_test.go              |   2 +
 eval/compile_effect.go                    |   6 +-
 eval/compile_lvalue.go                    |  38 ++++----
 eval/compile_value.go                     |  27 +++---
 eval/compile_value_test.go                |  45 +++++++++
 eval/compiler.go                          | 113 ++++++++--------------
 eval/eval_test.go                         |   4 -
 eval/purely_eval.go                       |   6 +-
 eval/resolve.go                           | 111 +++++++++------------
 eval/resolve_test.go                      |  18 ----
 eval/variable_ref.go                      | 109 +++++++++++----------
 eval/variable_ref_test.go                 |  79 +++++++++++++++
 19 files changed, 375 insertions(+), 318 deletions(-)
 delete mode 100644 eval/resolve_test.go
 create mode 100644 eval/variable_ref_test.go

diff --git a/cliedit/highlight_deps.go b/cliedit/highlight_deps.go
index c66a73a8..d774a05a 100644
--- a/cliedit/highlight_deps.go
+++ b/cliedit/highlight_deps.go
@@ -3,7 +3,6 @@ package cliedit
 import (
 	"os"
 	"os/exec"
-	"strings"
 
 	"github.com/elves/elvish/eval"
 	"github.com/elves/elvish/parse"
@@ -32,23 +31,24 @@ func hasCommand(ev *eval.Evaler, cmd string) bool {
 		return isDirOrExecutable(cmd) || hasExternalCommand(cmd)
 	}
 
-	explode, ns, name := eval.ParseVariableRef(cmd)
-	if explode {
+	sigil, qname := eval.SplitVariableRef(cmd)
+	if sigil != "" {
 		// The @ sign is only valid when referring to external commands.
 		return hasExternalCommand(cmd)
 	}
 
-	switch ns {
-	case "e":
-		return hasExternalCommand(name)
+	firstNs, rest := eval.SplitIncompleteQNameFirstNs(qname)
+	switch firstNs {
+	case "e:":
+		return hasExternalCommand(rest)
 	case "":
 		// Unqualified name; try builtin and global.
-		if hasFn(ev.Builtin, name) || hasFn(ev.Global, name) {
+		if hasFn(ev.Builtin, rest) || hasFn(ev.Global, rest) {
 			return true
 		}
 	default:
 		// Qualified name. Find the top-level module first.
-		if hasQualifiedFn(ev, strings.Split(ns, ":"), name) {
+		if hasQualifiedFn(ev, firstNs, rest) {
 			return true
 		}
 	}
@@ -57,10 +57,10 @@ func hasCommand(ev *eval.Evaler, cmd string) bool {
 	return hasExternalCommand(cmd)
 }
 
-func hasQualifiedFn(ev *eval.Evaler, nsParts []string, name string) bool {
-	modVar := ev.Global[nsParts[0]+eval.NsSuffix]
+func hasQualifiedFn(ev *eval.Evaler, firstNs string, rest string) bool {
+	modVar := ev.Global[firstNs]
 	if modVar == nil {
-		modVar = ev.Builtin[nsParts[0]+eval.NsSuffix]
+		modVar = ev.Builtin[firstNs]
 		if modVar == nil {
 			return false
 		}
@@ -69,8 +69,9 @@ func hasQualifiedFn(ev *eval.Evaler, nsParts []string, name string) bool {
 	if !ok {
 		return false
 	}
-	for _, nsPart := range nsParts[1:] {
-		modVar = mod[nsPart+eval.NsSuffix]
+	segs := eval.SplitQNameNsSegs(rest)
+	for _, seg := range segs[:len(segs)-1] {
+		modVar = mod[seg]
 		if modVar == nil {
 			return false
 		}
@@ -79,7 +80,7 @@ func hasQualifiedFn(ev *eval.Evaler, nsParts []string, name string) bool {
 			return false
 		}
 	}
-	return hasFn(mod, name)
+	return hasFn(mod, segs[len(segs)-1])
 }
 
 func hasFn(ns eval.Ns, name string) bool {
diff --git a/edit/completion/complete_command.go b/edit/completion/complete_command.go
index ada77c79..7eb7df5d 100644
--- a/edit/completion/complete_command.go
+++ b/edit/completion/complete_command.go
@@ -72,17 +72,18 @@ func complFormHeadInner(head string, ev *eval.Evaler, rawCands chan<- rawCandida
 	for special := range eval.IsBuiltinSpecial {
 		got(special)
 	}
-	explode, ns, _ := eval.ParseIncompleteVariableRef(head)
-	if !explode {
+	sigil, qname := eval.SplitVariableRef(head)
+	ns, _ := eval.SplitQNameNsIncomplete(qname)
+	if sigil == "" {
 		logger.Printf("completing commands in ns %q", ns)
 		ev.EachVariableInTop(ns, func(varname string) {
 			switch {
 			case strings.HasSuffix(varname, eval.FnSuffix):
-				got(eval.MakeVariableRef(false, ns, varname[:len(varname)-len(eval.FnSuffix)]))
+				got(ns + varname[:len(varname)-len(eval.FnSuffix)])
 			case strings.HasSuffix(varname, eval.NsSuffix):
-				got(eval.MakeVariableRef(false, ns, varname))
+				got(ns + varname)
 			default:
-				name := eval.MakeVariableRef(false, ns, varname)
+				name := ns + varname
 				rawCands <- &complexCandidate{name, " = ", " = ", ui.Styles{}}
 			}
 		})
diff --git a/edit/completion/complete_variable.go b/edit/completion/complete_variable.go
index 95b88b8a..6e4cedaf 100644
--- a/edit/completion/complete_variable.go
+++ b/edit/completion/complete_variable.go
@@ -9,7 +9,7 @@ import (
 
 type variableComplContext struct {
 	complContextCommon
-	ns, nsPart string
+	ns string
 }
 
 func (*variableComplContext) name() string { return "variable" }
@@ -17,16 +17,14 @@ func (*variableComplContext) name() string { return "variable" }
 func findVariableComplContext(n parse.Node, _ pureEvaler) complContext {
 	primary, ok := n.(*parse.Primary)
 	if ok && primary.Type == parse.Variable {
-		explode, nsPart, nameSeed := eval.SplitIncompleteVariableRef(primary.Value)
+		sigil, qname := eval.SplitVariableRef(primary.Value)
+		ns, nameSeed := eval.SplitQNameNsIncomplete(qname)
+
 		// Move past "$", "@" and "<ns>:".
-		begin := primary.Range().From + 1 + len(explode) + len(nsPart)
-		ns := nsPart
-		if len(ns) > 0 {
-			ns = ns[:len(ns)-1]
-		}
+		begin := primary.Range().From + 1 + len(sigil) + len(ns)
 		return &variableComplContext{
 			complContextCommon{nameSeed, parse.Bareword, begin, primary.Range().To},
-			ns, nsPart,
+			ns,
 		}
 	}
 	return nil
@@ -38,21 +36,20 @@ type evalerScopes interface {
 }
 
 func (ctx *variableComplContext) generate(env *complEnv, ch chan<- rawCandidate) error {
-	complVariable(ctx.ns, ctx.nsPart, env.evaler, ch)
+	complVariable(ctx.ns, env.evaler, ch)
 	return nil
 }
 
-func complVariable(ctxNs, ctxNsPart string, ev evalerScopes, ch chan<- rawCandidate) {
+func complVariable(ctxNs string, ev evalerScopes, ch chan<- rawCandidate) {
 	ev.EachVariableInTop(ctxNs, func(varname string) {
 		ch <- noQuoteCandidate(varname)
 	})
 
 	ev.EachNsInTop(func(ns string) {
-		nsPart := ns + ":"
 		// This is to match namespaces that are "nested" under the current
 		// namespace.
-		if hasProperPrefix(nsPart, ctxNsPart) {
-			ch <- noQuoteCandidate(nsPart[len(ctxNsPart):])
+		if hasProperPrefix(ns, ctxNs) {
+			ch <- noQuoteCandidate(ns[len(ctxNs):])
 		}
 	})
 }
diff --git a/edit/completion/complete_variable_test.go b/edit/completion/complete_variable_test.go
index a344b81a..3fc4332b 100644
--- a/edit/completion/complete_variable_test.go
+++ b/edit/completion/complete_variable_test.go
@@ -11,13 +11,13 @@ import (
 func TestFindVariableComplContext(t *testing.T) {
 	testComplContextFinder(t, "findVariableComplContext", findVariableComplContext, []complContextFinderTest{
 		{"$", &variableComplContext{
-			complContextCommon{"", parse.Bareword, 1, 1}, "", ""}},
+			complContextCommon{"", parse.Bareword, 1, 1}, ""}},
 		{"$a", &variableComplContext{
-			complContextCommon{"a", parse.Bareword, 1, 2}, "", ""}},
+			complContextCommon{"a", parse.Bareword, 1, 2}, ""}},
 		{"$a:", &variableComplContext{
-			complContextCommon{"", parse.Bareword, 3, 3}, "a", "a:"}},
+			complContextCommon{"", parse.Bareword, 3, 3}, "a:"}},
 		{"$a:b", &variableComplContext{
-			complContextCommon{"b", parse.Bareword, 3, 4}, "a", "a:"}},
+			complContextCommon{"b", parse.Bareword, 3, 4}, "a:"}},
 		// Wrong contexts
 		{"", nil},
 		{"echo", nil},
@@ -27,9 +27,9 @@ func TestFindVariableComplContext(t *testing.T) {
 type testEvalerScopes struct{}
 
 var testScopes = map[string]map[string]int{
-	"":        {"veni": 0, "vidi": 0, "vici": 0},
-	"foo":     {"lorem": 0, "ipsum": 0},
-	"foo:bar": {"lorem": 0, "dolor": 0},
+	"":         {"veni": 0, "vidi": 0, "vici": 0},
+	"foo:":     {"lorem": 0, "ipsum": 0},
+	"foo:bar:": {"lorem": 0, "dolor": 0},
 }
 
 func (testEvalerScopes) EachNsInTop(f func(string)) {
@@ -47,38 +47,37 @@ func (testEvalerScopes) EachVariableInTop(ns string, f func(string)) {
 }
 
 var complVariableTests = []struct {
-	ns     string
-	nsPart string
-	want   []rawCandidate
+	ns   string
+	want []rawCandidate
 }{
 	// No namespace: complete variables and namespaces
-	{"", "", []rawCandidate{
+	{"", []rawCandidate{
 		noQuoteCandidate("foo:"), noQuoteCandidate("foo:bar:"),
 		noQuoteCandidate("veni"), noQuoteCandidate("vici"), noQuoteCandidate("vidi"),
 	}},
 	// Nonempty namespace: complete variables in namespace and subnamespaces
 	// (but not variables in subnamespaces)
-	{"foo", "foo:", []rawCandidate{
+	{"foo:", []rawCandidate{
 		noQuoteCandidate("bar:"),
 		noQuoteCandidate("ipsum"), noQuoteCandidate("lorem"),
 	}},
 	// Bad namespace
-	{"bad", "bad:", nil},
+	{"bad:", nil},
 }
 
 func TestComplVariable(t *testing.T) {
 	for _, test := range complVariableTests {
-		got := collectComplVariable(test.ns, test.nsPart, testEvalerScopes{})
+		got := collectComplVariable(test.ns, testEvalerScopes{})
 		if !reflect.DeepEqual(got, test.want) {
-			t.Errorf("complVariable(%q, %q, ...) => %v, want %v", test.ns, test.nsPart, got, test.want)
+			t.Errorf("complVariable(%q, ...) => %v, want %v", test.ns, got, test.want)
 		}
 	}
 }
 
-func collectComplVariable(ns, nsPart string, ev evalerScopes) []rawCandidate {
+func collectComplVariable(ns string, ev evalerScopes) []rawCandidate {
 	ch := make(chan rawCandidate)
 	go func() {
-		complVariable(ns, nsPart, ev, ch)
+		complVariable(ns, ev, ch)
 		close(ch)
 	}()
 	var results []rawCandidate
diff --git a/edit/edcore/highlight.go b/edit/edcore/highlight.go
index 220b9094..de24ade0 100644
--- a/edit/edcore/highlight.go
+++ b/edit/edcore/highlight.go
@@ -25,10 +25,11 @@ func goodFormHead(head string, ed *editor) bool {
 		return util.IsExecutable(head) || isDir(head)
 	} else {
 		ev := ed.evaler
-		explode, ns, name := eval.ParseVariableRef(head)
-		if !explode {
+		sigil, qname := eval.SplitVariableRef(head)
+		ns, name := eval.SplitIncompleteQNameFirstNs(qname)
+		if sigil == "" {
 			switch ns {
-			case "":
+			case "", ":":
 				if ev.Builtin[name+eval.FnSuffix] != nil || ev.Global[name+eval.FnSuffix] != nil {
 					return true
 				}
diff --git a/eval/builtin_fn_misc.go b/eval/builtin_fn_misc.go
index 29ca4a96..0f0fa809 100644
--- a/eval/builtin_fn_misc.go
+++ b/eval/builtin_fn_misc.go
@@ -70,9 +70,9 @@ func resolve(fm *Frame, head string) string {
 	if special {
 		return "special"
 	}
-	explode, ns, name := ParseVariableRef(head)
-	if !explode && fm.ResolveVar(ns, name+FnSuffix) != nil {
-		return "$" + head + FnSuffix
+	sigil, qname := SplitVariableRef(head)
+	if sigil == "" && fm.ResolveVar(qname+FnSuffix) != nil {
+		return "$" + qname + FnSuffix
 	}
 	return "(external " + parse.Quote(head) + ")"
 }
diff --git a/eval/builtin_special.go b/eval/builtin_special.go
index 9b613a7a..f90133c0 100644
--- a/eval/builtin_special.go
+++ b/eval/builtin_special.go
@@ -84,33 +84,34 @@ func compileDel(cp *compiler, fn *parse.Form) effectOpBody {
 			continue
 		}
 
-		explode, ns, name := ParseVariableRef(head.Value)
-		if explode {
-			cp.errorf("arguments to del may be have a leading @")
+		sigil, qname := SplitVariableRef(head.Value)
+		if sigil != "" {
+			cp.errorf("arguments to del may not have a sigils, got %q", sigil)
 			continue
 		}
 		var f effectOpBody
 		if len(indicies) == 0 {
+			ns, name := SplitQNameNsFirst(qname)
 			switch ns {
-			case "", "local":
+			case "", ":", "local:":
 				if !cp.thisScope().has(name) {
 					cp.errorf("no variable $%s in local scope", name)
 					continue
 				}
 				cp.thisScope().del(name)
 				f = delLocalVarOp{name}
-			case "E":
+			case "E:":
 				f = delEnvVarOp{name}
 			default:
 				cp.errorf("only variables in local: or E: can be deleted")
 				continue
 			}
 		} else {
-			if !cp.registerVariableGet(ns, name) {
+			if !cp.registerVariableGet(qname) {
 				cp.errorf("no variable $%s", head.Value)
 				continue
 			}
-			f = newDelElementOp(ns, name, head.Range().From, head.Range().To, cp.arrayOps(indicies))
+			f = newDelElementOp(qname, head.Range().From, head.Range().To, cp.arrayOps(indicies))
 		}
 		ops = append(ops, effectOp{f, cn.Range().From, cn.Range().To})
 	}
@@ -130,18 +131,17 @@ func (op delEnvVarOp) invoke(*Frame) error {
 	return os.Unsetenv(op.name)
 }
 
-func newDelElementOp(ns, name string, begin, headEnd int, indexOps []valuesOp) effectOpBody {
+func newDelElementOp(qname string, begin, headEnd int, indexOps []valuesOp) effectOpBody {
 	ends := make([]int, len(indexOps)+1)
 	ends[0] = headEnd
 	for i, op := range indexOps {
 		ends[i+1] = op.end
 	}
-	return &delElemOp{ns, name, indexOps, begin, ends}
+	return &delElemOp{qname, indexOps, begin, ends}
 }
 
 type delElemOp struct {
-	ns       string
-	name     string
+	qname    string
 	indexOps []valuesOp
 	begin    int
 	ends     []int
@@ -159,7 +159,7 @@ func (op *delElemOp) invoke(fm *Frame) error {
 		}
 		indicies = append(indicies, indexValues[0])
 	}
-	err := vars.DelElement(fm.ResolveVar(op.ns, op.name), indicies)
+	err := vars.DelElement(fm.ResolveVar(op.qname), indicies)
 	if err != nil {
 		if level := vars.ElementErrorLevel(err); level >= 0 {
 			return fm.errorpf(op.begin, op.ends[level], "%s", err.Error())
@@ -179,7 +179,7 @@ func compileFn(cp *compiler, fn *parse.Form) effectOpBody {
 	bodyNode := args.nextMustLambda()
 	args.mustEnd()
 
-	cp.registerVariableSetQname(":" + varName)
+	cp.registerVariableSet(":" + varName)
 	op := cp.lambda(bodyNode)
 
 	return fnOp{varName, op}
diff --git a/eval/builtin_special_test.go b/eval/builtin_special_test.go
index ee5e7a42..7fda6e46 100644
--- a/eval/builtin_special_test.go
+++ b/eval/builtin_special_test.go
@@ -87,6 +87,8 @@ func TestUse(t *testing.T) {
 		// That(`{ use lorem }; put $lorem:name`).ErrorsAny(),
 
 		// use of imported variable is captured in upvalue
+		That(`use lorem; { put $lorem:name }`).Puts("lorem"),
+		That(`{ use lorem; { put $lorem:name } }`).Puts("lorem"),
 		That(`({ use lorem; put { { put $lorem:name } } })`).Puts("lorem"),
 		// use of imported function is also captured in upvalue
 		That(`{ use lorem; { lorem:put-name } }`).Puts("lorem"),
diff --git a/eval/compile_effect.go b/eval/compile_effect.go
index 75dc64ee..73db48d5 100644
--- a/eval/compile_effect.go
+++ b/eval/compile_effect.go
@@ -175,10 +175,10 @@ func (cp *compiler) form(n *parse.Form) effectOpBody {
 				specialOpFunc = compileForm(cp, n)
 			} else {
 				var headOpFunc valuesOpBody
-				explode, ns, name := ParseVariableRef(headStr)
-				if !explode && cp.registerVariableGet(ns, name+FnSuffix) {
+				sigil, qname := SplitVariableRef(headStr)
+				if sigil == "" && cp.registerVariableGet(qname+FnSuffix) {
 					// $head~ resolves.
-					headOpFunc = variableOp{false, ns, name + FnSuffix}
+					headOpFunc = variableOp{false, qname + FnSuffix}
 				} else {
 					// Fall back to $e:head~.
 					headOpFunc = literalValues(ExternalCmd{headStr})
diff --git a/eval/compile_lvalue.go b/eval/compile_lvalue.go
index 9c86e0b4..55a03c5f 100644
--- a/eval/compile_lvalue.go
+++ b/eval/compile_lvalue.go
@@ -75,17 +75,19 @@ func (cp *compiler) lvaluesMulti(nodes []*parse.Compound) (lvaluesOp, lvaluesOp)
 }
 
 func (cp *compiler) lvalueBase(n *parse.Indexing, msg string) (bool, lvaluesOpBody) {
-	qname := cp.literal(n.Head, msg)
-	explode, ns, name := ParseVariableRef(qname)
+	ref := cp.literal(n.Head, msg)
+	sigil, qname := SplitVariableRef(ref)
+	// TODO: Deal with other sigils too
+	explode := sigil != ""
 	if len(n.Indicies) == 0 {
-		cp.registerVariableSet(ns, name)
-		return explode, varOp{ns, name}
+		cp.registerVariableSet(qname)
+		return explode, varOp{qname}
 	}
-	return explode, cp.lvalueElement(ns, name, n)
+	return explode, cp.lvalueElement(qname, n)
 }
 
-func (cp *compiler) lvalueElement(ns, name string, n *parse.Indexing) lvaluesOpBody {
-	cp.registerVariableGet(ns, name)
+func (cp *compiler) lvalueElement(qname string, n *parse.Indexing) lvaluesOpBody {
+	cp.registerVariableGet(qname)
 
 	begin, end := n.Range().From, n.Range().To
 	ends := make([]int, len(n.Indicies)+1)
@@ -96,7 +98,7 @@ func (cp *compiler) lvalueElement(ns, name string, n *parse.Indexing) lvaluesOpB
 
 	indexOps := cp.arrayOps(n.Indicies)
 
-	return &elemOp{ns, name, indexOps, begin, end, ends}
+	return &elemOp{qname, indexOps, begin, end, ends}
 }
 
 type seqLValuesOpBody struct {
@@ -116,26 +118,27 @@ func (op seqLValuesOpBody) invoke(fm *Frame) ([]vars.Var, error) {
 }
 
 type varOp struct {
-	ns, name string
+	qname string
 }
 
 func (op varOp) invoke(fm *Frame) ([]vars.Var, error) {
-	variable := fm.ResolveVar(op.ns, op.name)
+	variable := fm.ResolveVar(op.qname)
 	if variable == nil {
-		if op.ns == "" || op.ns == "local" {
+		ns, name := SplitQNameNs(op.qname)
+		if ns == "" || ns == ":" || ns == "local:" {
 			// New variable.
 			// XXX We depend on the fact that this variable will
 			// immeidately be set.
-			if strings.HasSuffix(op.name, FnSuffix) {
+			if strings.HasSuffix(name, FnSuffix) {
 				val := Callable(nil)
 				variable = vars.FromPtr(&val)
-			} else if strings.HasSuffix(op.name, NsSuffix) {
+			} else if strings.HasSuffix(name, NsSuffix) {
 				val := Ns(nil)
 				variable = vars.FromPtr(&val)
 			} else {
 				variable = vars.FromInit(nil)
 			}
-			fm.local[op.name] = variable
+			fm.local[name] = variable
 		} else {
 			return nil, fmt.Errorf("new variables can only be created in local scope")
 		}
@@ -144,8 +147,7 @@ func (op varOp) invoke(fm *Frame) ([]vars.Var, error) {
 }
 
 type elemOp struct {
-	ns       string
-	name     string
+	qname    string
 	indexOps []valuesOp
 	begin    int
 	end      int
@@ -153,9 +155,9 @@ type elemOp struct {
 }
 
 func (op *elemOp) invoke(fm *Frame) ([]vars.Var, error) {
-	variable := fm.ResolveVar(op.ns, op.name)
+	variable := fm.ResolveVar(op.qname)
 	if variable == nil {
-		return nil, fmt.Errorf("variable $%s:%s does not exist, compiler bug", op.ns, op.name)
+		return nil, fmt.Errorf("variable $%s does not exist, compiler bug", op.qname)
 	}
 
 	indicies := make([]interface{}, len(op.indexOps))
diff --git a/eval/compile_value.go b/eval/compile_value.go
index 73aff08e..8147e392 100644
--- a/eval/compile_value.go
+++ b/eval/compile_value.go
@@ -221,11 +221,11 @@ func (cp *compiler) primary(n *parse.Primary) valuesOpBody {
 	case parse.Bareword, parse.SingleQuoted, parse.DoubleQuoted:
 		return literalStr(n.Value)
 	case parse.Variable:
-		explode, ns, name := ParseVariableRef(n.Value)
-		if !cp.registerVariableGet(ns, name) {
-			cp.errorf("variable $%s not found", n.Value)
+		sigil, qname := SplitVariableRef(n.Value)
+		if !cp.registerVariableGet(qname) {
+			cp.errorf("variable $%s not found", qname)
 		}
-		return &variableOp{explode, ns, name}
+		return &variableOp{sigil != "", qname}
 	case parse.Wildcard:
 		seg, err := wildcardToSegment(n.SourceText())
 		if err != nil {
@@ -257,14 +257,13 @@ func (cp *compiler) primary(n *parse.Primary) valuesOpBody {
 
 type variableOp struct {
 	explode bool
-	ns      string
-	name    string
+	qname   string
 }
 
 func (op variableOp) invoke(fm *Frame) ([]interface{}, error) {
-	variable := fm.ResolveVar(op.ns, op.name)
+	variable := fm.ResolveVar(op.qname)
 	if variable == nil {
-		return nil, fmt.Errorf("variable $%s:%s not found", op.ns, op.name)
+		return nil, fmt.Errorf("variable $%s not found", op.qname)
 	}
 	value := variable.Get()
 	if op.explode {
@@ -390,8 +389,10 @@ func (cp *compiler) lambda(n *parse.Primary) valuesOpBody {
 		// Argument list.
 		argNames = make([]string, len(n.Elements))
 		for i, arg := range n.Elements {
-			qname := mustString(cp, arg, "argument name must be literal string")
-			explode, ns, name := ParseVariableRef(qname)
+			ref := mustString(cp, arg, "argument name must be literal string")
+			sigil, qname := SplitVariableRef(ref)
+			explode := sigil != ""
+			ns, name := SplitQNameNs(qname)
 			if ns != "" {
 				cp.errorpf(arg.Range().From, arg.Range().To, "argument name must be unqualified")
 			}
@@ -414,7 +415,7 @@ func (cp *compiler) lambda(n *parse.Primary) valuesOpBody {
 		optDefaultOps = make([]valuesOp, len(n.MapPairs))
 		for i, opt := range n.MapPairs {
 			qname := mustString(cp, opt.Key, "option name must be literal string")
-			_, ns, name := ParseVariableRef(qname)
+			ns, name := SplitQNameNs(qname)
 			if ns != "" {
 				cp.errorpf(opt.Key.Range().From, opt.Key.Range().To, "option name must be unqualified")
 			}
@@ -449,7 +450,7 @@ func (cp *compiler) lambda(n *parse.Primary) valuesOpBody {
 	cp.popScope()
 
 	for name := range capture {
-		cp.registerVariableGetQname(name)
+		cp.registerVariableGet(name)
 	}
 
 	return &lambdaOp{argNames, restArgName, optNames, optDefaultOps, capture, subop, cp.srcMeta, n.Range().From, n.Range().To}
@@ -470,7 +471,7 @@ type lambdaOp struct {
 func (op *lambdaOp) invoke(fm *Frame) ([]interface{}, error) {
 	evCapture := make(Ns)
 	for name := range op.capture {
-		evCapture[name] = fm.ResolveVar("", name)
+		evCapture[name] = fm.ResolveVar(":" + name)
 	}
 	optDefaults := make([]interface{}, len(op.optDefaultOps))
 	for i, op := range op.optDefaultOps {
diff --git a/eval/compile_value_test.go b/eval/compile_value_test.go
index 0266e38a..9d220861 100644
--- a/eval/compile_value_test.go
+++ b/eval/compile_value_test.go
@@ -49,6 +49,51 @@ func TestCompileValue(t *testing.T) {
 		// Splicing
 		That("x=[elvish rules]; put $@x").Puts("elvish", "rules"),
 
+		// Variable namespace
+		// ------------------
+
+		// Pseudo-namespace local: accesses the local scope.
+		That("x = outer; { local:x = inner; put $local:x }").Puts("inner"),
+		// Pseudo-namespace up: accesses upvalues.
+		That("x = outer; { local:x = inner; put $up:x }").Puts("outer"),
+		// Pseudo-namespace builtin: accesses builtins.
+		That("put $builtin:true").Puts(true),
+		// Unqualified name prefers local: to up:.
+		That("x = outer; { local:x = inner; put $x }").Puts("inner"),
+		// Unqualified name resolves to upvalue if no local name exists.
+		That("x = outer; { put $x }").Puts("outer"),
+		// Unqualified name resolves to builtin if no local name or upvalue
+		// exists.
+		That("put $true").Puts(true),
+		// A name can be explicitly unqualified by having a leading colon.
+		That("x = val; put $:x").Puts("val"),
+		That("put $:true").Puts(true),
+
+		// Pseudo-namespace E: provides read-write access to environment
+		// variables. Colons inside the name are supported.
+		That("set-env a:b VAL; put $E:a:b").Puts("VAL"),
+		That("E:a:b = VAL2; get-env a:b").Puts("VAL2"),
+
+		// Pseudo-namespace e: provides readonly access to external commands.
+		// Only names ending in ~ are resolved, and resolution always succeeds
+		// regardless of whether the command actually exists. Colons inside the
+		// name are supported.
+		That("put $e:a:b~").Puts(ExternalCmd{Name: "a:b"}),
+
+		// A "normal" namespace access indexes the namespace as a variable.
+		That("ns: = (ns [&a= val]); put $ns:a").Puts("val"),
+		// Multi-level namespace access is supported.
+		That("ns: = (ns [&a:= (ns [&b= val])]); put $ns:a:b").Puts("val"),
+		// Multi-level namespace access can have a leading colon to signal that
+		// the first component is unqualified.
+		That("ns: = (ns [&a:= (ns [&b= val])]); put $:ns:a:b").Puts("val"),
+		// Multi-level namespace access can be combined with the local:
+		// pseudo-namespaces.
+		That("ns: = (ns [&a:= (ns [&b= val])]); put $local:ns:a:b").Puts("val"),
+		// Multi-level namespace access can be combined with the up:
+		// pseudo-namespaces.
+		That("ns: = (ns [&a:= (ns [&b= val])]); { put $up:ns:a:b }").Puts("val"),
+
 		// Tilde
 		// -----
 		That("h=$E:HOME; E:HOME=/foo; put ~ ~/src; E:HOME=$h").Puts("/foo", "/foo/src"),
diff --git a/eval/compiler.go b/eval/compiler.go
index 77c3f91d..f6839898 100644
--- a/eval/compiler.go
+++ b/eval/compiler.go
@@ -60,56 +60,18 @@ func (cp *compiler) popScope() {
 	cp.scopes = cp.scopes[:len(cp.scopes)-1]
 }
 
-func (cp *compiler) registerVariableGetQname(qname string) bool {
-	_, ns, name := ParseVariableRef(qname)
-	return cp.registerVariableGet(ns, name)
+func (cp *compiler) registerVariableSet(qname string) bool {
+	return cp.registerVariableAccess(qname, true)
 }
 
-func (cp *compiler) registerVariableGet(ns, name string) bool {
-	switch ns {
-	case "", "local", "up":
-		// Handled below
-	case "e", "E":
-		return true
-	default:
-		return cp.registerModAccess(ns)
-	}
-	// Find in local scope
-	if ns == "" || ns == "local" {
-		if cp.thisScope().has(name) {
-			return true
-		}
-	}
-	// Find in upper scopes
-	if ns == "" || ns == "up" {
-		for i := len(cp.scopes) - 2; i >= 0; i-- {
-			if cp.scopes[i].has(name) {
-				// Existing name: record capture and return.
-				cp.capture.set(name)
-				return true
-			}
-		}
-	}
-	// Find in builtin scope
-	if ns == "" || ns == "builtin" {
-		if cp.builtin.has(name) {
-			return true
-		}
-	}
-	return false
+func (cp *compiler) registerVariableGet(qname string) bool {
+	return cp.registerVariableAccess(qname, false)
 }
 
-func (cp *compiler) registerVariableSetQname(qname string) bool {
-	_, ns, name := ParseVariableRef(qname)
-	return cp.registerVariableSet(ns, name)
-}
+func (cp *compiler) registerVariableAccess(qname string, set bool) bool {
+	readLocal := func(name string) bool { return cp.thisScope().has(name) }
 
-func (cp *compiler) registerVariableSet(ns, name string) bool {
-	switch ns {
-	case "local":
-		cp.thisScope().set(name)
-		return true
-	case "up":
+	readUpvalue := func(name string) bool {
 		for i := len(cp.scopes) - 2; i >= 0; i-- {
 			if cp.scopes[i].has(name) {
 				// Existing name: record capture and return.
@@ -118,36 +80,43 @@ func (cp *compiler) registerVariableSet(ns, name string) bool {
 			}
 		}
 		return false
-	case "builtin":
-		cp.errorf("cannot set builtin variable")
-		return false
-	case "":
-		if cp.thisScope().has(name) {
-			// A name on current scope. Do nothing.
+	}
+
+	readBuiltin := func(name string) bool { return cp.builtin.has(name) }
+
+	readNonPseudo := func(name string) bool {
+		return readLocal(name) || readUpvalue(name) || readBuiltin(name)
+	}
+
+	createLocal := func(name string) bool {
+		if set && name != "" && !strings.ContainsRune(name[:len(name)-1], ':') {
+			cp.thisScope().set(name)
 			return true
 		}
-		// Walk up the upper scopes
-		for i := len(cp.scopes) - 2; i >= 0; i-- {
-			if cp.scopes[i].has(name) {
-				// Existing name. Do nothing
-				cp.capture.set(name)
-				return true
-			}
-		}
-		// New name. Register on this scope!
-		cp.thisScope().set(name)
-		return true
-	case "e", "E":
-		// Special namespaces, do nothing
-		return true
-	default:
-		return cp.registerModAccess(ns)
+		return false
 	}
-}
 
-func (cp *compiler) registerModAccess(name string) bool {
-	if strings.ContainsRune(name, ':') {
-		name = name[:strings.IndexByte(name, ':')]
+	ns, name := SplitQNameNsFirst(qname) // ns = "", name = "ns:"
+	name1 := name                        // name1 = "ns:"
+	if name != "" && strings.ContainsRune(name[:len(name)-1], ':') {
+		name1, _ = SplitQNameNsFirst(name)
+	}
+
+	// This switch mirrors the structure of that from (*Frame).ResoleVar.
+	switch ns {
+	case "E:":
+		return true
+	case "e:":
+		return !set && strings.HasSuffix(name, FnSuffix)
+	case "local:":
+		return readLocal(name1) || createLocal(name)
+	case "up:":
+		return readUpvalue(name1)
+	case "builtin:":
+		return readBuiltin(name1)
+	case "", ":":
+		return readNonPseudo(name1) || createLocal(name)
+	default:
+		return readNonPseudo(ns)
 	}
-	return cp.registerVariableGet("", name+NsSuffix)
 }
diff --git a/eval/eval_test.go b/eval/eval_test.go
index fb58b912..63801142 100644
--- a/eval/eval_test.go
+++ b/eval/eval_test.go
@@ -28,10 +28,6 @@ func TestNumBgJobs(t *testing.T) {
 
 func TestMiscEval(t *testing.T) {
 	Test(t,
-		// Pseudo-namespaces local: and up:
-		That("x=lorem; { local:x=ipsum; put $up:x $local:x }").Puts(
-			"lorem", "ipsum"),
-		That("x=lorem; { up:x=ipsum; put $x }; put $x").Puts("ipsum", "ipsum"),
 		// Pseudo-namespace E:
 		That("E:FOO=lorem; put $E:FOO").Puts("lorem"),
 		That("del E:FOO; put $E:FOO").Puts(""),
diff --git a/eval/purely_eval.go b/eval/purely_eval.go
index 5324d2c1..c049351d 100644
--- a/eval/purely_eval.go
+++ b/eval/purely_eval.go
@@ -72,12 +72,12 @@ func (ev *Evaler) PurelyEvalPrimary(pn *parse.Primary) interface{} {
 	case parse.Bareword, parse.SingleQuoted, parse.DoubleQuoted:
 		return pn.Value
 	case parse.Variable:
-		explode, ns, name := ParseVariableRef(pn.Value)
-		if explode {
+		sigil, qname := SplitVariableRef(pn.Value)
+		if sigil != "" {
 			return nil
 		}
 		ec := NewTopFrame(ev, NewInternalSource("[purely eval]"), nil)
-		variable := ec.ResolveVar(ns, name)
+		variable := ec.ResolveVar(qname)
 		if variable != nil {
 			return variable.Get()
 		}
diff --git a/eval/resolve.go b/eval/resolve.go
index c1c5d085..83946af9 100644
--- a/eval/resolve.go
+++ b/eval/resolve.go
@@ -13,29 +13,29 @@ import (
 // namespace ns that can be found from the top context.
 func (ev *evalerScopes) EachVariableInTop(ns string, f func(s string)) {
 	switch ns {
-	case "builtin":
+	case "builtin:":
 		for name := range ev.Builtin {
 			f(name)
 		}
-	case "":
+	case "", ":":
 		for name := range ev.Global {
 			f(name)
 		}
 		for name := range ev.Builtin {
 			f(name)
 		}
-	case "e":
+	case "e:":
 		EachExternal(func(cmd string) {
 			f(cmd + FnSuffix)
 		})
-	case "E":
+	case "E:":
 		for _, s := range os.Environ() {
 			if i := strings.IndexByte(s, '='); i > 0 {
 				f(s[:i])
 			}
 		}
 	default:
-		segs := splitQName(ns + NsSuffix)
+		segs := SplitQNameNsSegs(ns)
 		mod := ev.Global[segs[0]]
 		if mod == nil {
 			mod = ev.Builtin[segs[0]]
@@ -57,90 +57,73 @@ func (ev *evalerScopes) EachVariableInTop(ns string, f func(s string)) {
 // EachNsInTop calls the passed function for each namespace that can be used
 // from the top context.
 func (ev *evalerScopes) EachNsInTop(f func(s string)) {
-	f("builtin")
-	f("e")
-	f("E")
+	f("builtin:")
+	f("e:")
+	f("E:")
 
 	for name := range ev.Global {
 		if strings.HasSuffix(name, NsSuffix) {
-			f(name[:len(name)-len(NsSuffix)])
+			f(name)
 		}
 	}
 	for name := range ev.Builtin {
 		if strings.HasSuffix(name, NsSuffix) {
-			f(name[:len(name)-len(NsSuffix)])
+			f(name)
 		}
 	}
 }
 
 // ResolveVar resolves a variable. When the variable cannot be found, nil is
 // returned.
-func (fm *Frame) ResolveVar(n, name string) vars.Var {
-	if n == "" {
-		return fm.resolveUnqualified(name)
-	}
+func (fm *Frame) ResolveVar(qname string) vars.Var {
+	ns, name := SplitQNameNsFirst(qname)
 
-	// TODO: Let this function accept the fully qualified name.
-	segs := splitQName(n + ":" + name)
-
-	var ns Ns
-
-	switch segs[0] {
-	case "e:":
-		if len(segs) == 2 && strings.HasSuffix(segs[1], FnSuffix) {
-			return vars.NewReadOnly(ExternalCmd{Name: segs[1][:len(segs[1])-len(FnSuffix)]})
-		}
-		return nil
+	switch ns {
 	case "E:":
-		if len(segs) == 2 {
-			return vars.FromEnv(segs[1])
+		return vars.FromEnv(name)
+	case "e:":
+		if strings.HasSuffix(name, FnSuffix) {
+			return vars.NewReadOnly(ExternalCmd{name[:len(name)-len(FnSuffix)]})
 		}
 		return nil
 	case "local:":
-		ns = fm.local
+		return resolveNested(fm.local, name)
 	case "up:":
-		ns = fm.up
+		return resolveNested(fm.up, name)
 	case "builtin:":
-		ns = fm.Builtin
+		return resolveNested(fm.Builtin, name)
+	case "", ":":
+		return fm.resolveNonPseudo(name)
 	default:
-		v := fm.resolveUnqualified(segs[0])
-		if v == nil {
-			return nil
-		}
-		ns = v.Get().(Ns)
+		return fm.resolveNonPseudo(qname)
 	}
+}
 
-	for _, seg := range segs[1 : len(segs)-1] {
-		v := ns[seg]
-		if v == nil {
+func (fm *Frame) resolveNonPseudo(name string) vars.Var {
+	if v := resolveNested(fm.local, name); v != nil {
+		return v
+	}
+	if v := resolveNested(fm.up, name); v != nil {
+		return v
+	}
+	return resolveNested(fm.Builtin, name)
+}
+
+func resolveNested(ns Ns, name string) vars.Var {
+	if name == "" {
+		return nil
+	}
+	segs := SplitQNameNsSegs(name)
+	for _, seg := range segs[:len(segs)-1] {
+		variable := ns[seg]
+		if variable == nil {
 			return nil
 		}
-		ns = v.Get().(Ns)
+		nestedNs, ok := variable.Get().(Ns)
+		if !ok {
+			return nil
+		}
+		ns = nestedNs
 	}
 	return ns[segs[len(segs)-1]]
 }
-
-func splitQName(qname string) []string {
-	i := 0
-	var segs []string
-	for i < len(qname) {
-		j := strings.IndexByte(qname[i:], ':')
-		if j == -1 {
-			segs = append(segs, qname[i:])
-			break
-		}
-		segs = append(segs, qname[i:i+j+1])
-		i += j + 1
-	}
-	return segs
-}
-
-func (fm *Frame) resolveUnqualified(name string) vars.Var {
-	if v, ok := fm.local[name]; ok {
-		return v
-	}
-	if v, ok := fm.up[name]; ok {
-		return v
-	}
-	return fm.Builtin[name]
-}
diff --git a/eval/resolve_test.go b/eval/resolve_test.go
deleted file mode 100644
index c481d232..00000000
--- a/eval/resolve_test.go
+++ /dev/null
@@ -1,18 +0,0 @@
-package eval
-
-import (
-	"testing"
-
-	"github.com/elves/elvish/tt"
-)
-
-var splitQNameTests = tt.Table{
-	tt.Args("a").Rets([]string{"a"}),
-	tt.Args("a:b").Rets([]string{"a:", "b"}),
-	tt.Args("a:b:").Rets([]string{"a:", "b:"}),
-	tt.Args("a:b:c:d").Rets([]string{"a:", "b:", "c:", "d"}),
-}
-
-func TestSplitQName(t *testing.T) {
-	tt.Test(t, tt.Fn("splitQName", splitQName), splitQNameTests)
-}
diff --git a/eval/variable_ref.go b/eval/variable_ref.go
index bedf042e..48e32439 100644
--- a/eval/variable_ref.go
+++ b/eval/variable_ref.go
@@ -2,65 +2,64 @@ package eval
 
 import "strings"
 
-// ParseVariableRef parses a variable reference.
-func ParseVariableRef(text string) (explode bool, ns string, name string) {
-	return parseVariableRef(text, true)
-}
-
-// ParseIncompleteVariableRef parses an incomplete variable reference.
-func ParseIncompleteVariableRef(text string) (explode bool, ns string, name string) {
-	return parseVariableRef(text, false)
-}
-
-func parseVariableRef(text string, complete bool) (explode bool, ns string, name string) {
-	explodePart, nsPart, name := splitVariableRef(text, complete)
-	ns = nsPart
-	if len(ns) > 0 {
-		ns = ns[:len(ns)-1]
+// SplitVariableRef splits a variable reference into the sigil and the
+// (qualified) name.
+func SplitVariableRef(ref string) (sigil string, qname string) {
+	if ref == "" {
+		return "", ""
 	}
-	return explodePart != "", ns, name
-}
-
-// SplitVariableRef splits a variable reference into three parts: an optional
-// explode operator (either "" or "@"), a namespace part, and a name part.
-func SplitVariableRef(text string) (explodePart, nsPart, name string) {
-	return splitVariableRef(text, true)
-}
-
-// SplitIncompleteVariableRef splits an incomplete variable reference into three
-// parts: an optional explode operator (either "" or "@"), a namespace part, and
-// a name part.
-func SplitIncompleteVariableRef(text string) (explodePart, nsPart, name string) {
-	return splitVariableRef(text, false)
-}
-
-func splitVariableRef(text string, complete bool) (explodePart, nsPart, name string) {
-	if text == "" {
-		return "", "", ""
-	}
-	e, qname := "", text
-	if text[0] == '@' {
-		e = "@"
-		qname = text[1:]
+	switch ref[0] {
+	case '@':
+		// TODO(xiaq): Support % later.
+		return ref[:1], ref[1:]
+	default:
+		return "", ref
 	}
+}
+
+// SplitQNameNs splits a qualified variable name into the namespace part and the
+// name part.
+func SplitQNameNs(qname string) (ns, name string) {
 	if qname == "" {
-		return e, "", ""
+		return "", ""
 	}
-	i := strings.LastIndexByte(qname, ':')
-	if complete && i == len(qname)-1 {
-		i = strings.LastIndexByte(qname[:len(qname)-1], ':')
-	}
-	return e, qname[:i+1], qname[i+1:]
+	colon := strings.LastIndexByte(qname[:len(qname)-1], ':')
+	// If colon is -1, colon+1 will be 0, rendering an empty ns.
+	return qname[:colon+1], qname[colon+1:]
 }
 
-// MakeVariableRef builds a variable reference.
-func MakeVariableRef(explode bool, ns string, name string) string {
-	prefix := ""
-	if explode {
-		prefix = "@"
-	}
-	if ns != "" {
-		prefix += ns + ":"
-	}
-	return prefix + name
+// SplitQNameNs splits an incomplete qualified variable name into the namespace
+// part and the name part.
+func SplitQNameNsIncomplete(qname string) (ns, name string) {
+	colon := strings.LastIndexByte(qname, ':')
+	// If colon is -1, colon+1 will be 0, rendering an empty ns.
+	return qname[:colon+1], qname[colon+1:]
+}
+
+// SplitQNameNs splits a qualified variable name into the first part and the rest.
+func SplitQNameNsFirst(qname string) (ns, rest string) {
+	colon := strings.IndexByte(qname, ':')
+	if colon == len(qname)-1 {
+		// Unqualified variable ending with colon ($name:).
+		return "", qname
+	}
+	// If colon is -1, colon+1 will be 0, rendering an empty ns.
+	return qname[:colon+1], qname[colon+1:]
+}
+
+// SplitIncompleteQNameNsFirst splits an incomplete qualified variable name into
+// the first part and the rest.
+func SplitIncompleteQNameFirstNs(qname string) (ns, rest string) {
+	colon := strings.IndexByte(qname, ':')
+	// If colon is -1, colon+1 will be 0, rendering an empty ns.
+	return qname[:colon+1], qname[colon+1:]
+}
+
+// SplitQNameNsSegs splits a qualified name into namespace segments.
+func SplitQNameNsSegs(qname string) []string {
+	segs := strings.SplitAfter(qname, ":")
+	if len(segs) > 0 && segs[len(segs)-1] == "" {
+		segs = segs[:len(segs)-1]
+	}
+	return segs
 }
diff --git a/eval/variable_ref_test.go b/eval/variable_ref_test.go
new file mode 100644
index 00000000..1937647d
--- /dev/null
+++ b/eval/variable_ref_test.go
@@ -0,0 +1,79 @@
+package eval
+
+import (
+	"testing"
+
+	"github.com/elves/elvish/tt"
+)
+
+var Args = tt.Args
+
+func TestSplitVariableRef(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitVariableRef", SplitVariableRef), tt.Table{
+		Args("").Rets("", ""),
+		Args("x").Rets("", "x"),
+		Args("@x").Rets("@", "x"),
+		Args("a:b").Rets("", "a:b"),
+		Args("@a:b").Rets("@", "a:b"),
+	})
+}
+
+func TestSplitQNameNs(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitQNameNs", SplitQNameNs), tt.Table{
+		Args("").Rets("", ""),
+		Args("a").Rets("", "a"),
+		Args("a:").Rets("", "a:"),
+		Args("a:b").Rets("a:", "b"),
+		Args("a:b:").Rets("a:", "b:"),
+		Args("a:b:c").Rets("a:b:", "c"),
+		Args("a:b:c:").Rets("a:b:", "c:"),
+	})
+}
+
+func TestSplitQNameNsIncomplete(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitQNameNsIncomplete", SplitQNameNsIncomplete), tt.Table{
+		Args("").Rets("", ""),
+		Args("a").Rets("", "a"),
+		Args("a:").Rets("a:", ""),
+		Args("a:b").Rets("a:", "b"),
+		Args("a:b:").Rets("a:b:", ""),
+		Args("a:b:c").Rets("a:b:", "c"),
+		Args("a:b:c:").Rets("a:b:c:", ""),
+	})
+}
+
+func TestSplitQNameNsFirst(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitQNameNsFirst", SplitQNameNsFirst), tt.Table{
+		Args("").Rets("", ""),
+		Args("a").Rets("", "a"),
+		Args("a:").Rets("", "a:"),
+		Args("a:b").Rets("a:", "b"),
+		Args("a:b:").Rets("a:", "b:"),
+		Args("a:b:c").Rets("a:", "b:c"),
+		Args("a:b:c:").Rets("a:", "b:c:"),
+	})
+}
+
+func TestSplitIncompleteQNameFirstNs(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitIncompleteQNameFirstNs", SplitIncompleteQNameFirstNs), tt.Table{
+		Args("").Rets("", ""),
+		Args("a").Rets("", "a"),
+		Args("a:").Rets("a:", ""),
+		Args("a:b").Rets("a:", "b"),
+		Args("a:b:").Rets("a:", "b:"),
+		Args("a:b:c").Rets("a:", "b:c"),
+		Args("a:b:c:").Rets("a:", "b:c:"),
+	})
+}
+
+func TestSplitQNameNsSegs(t *testing.T) {
+	tt.Test(t, tt.Fn("SplitQNameNsSegs", SplitQNameNsSegs), tt.Table{
+		Args("").Rets([]string{}),
+		Args("a").Rets([]string{"a"}),
+		Args("a:").Rets([]string{"a:"}),
+		Args("a:b").Rets([]string{"a:", "b"}),
+		Args("a:b:").Rets([]string{"a:", "b:"}),
+		Args("a:b:c").Rets([]string{"a:", "b:", "c"}),
+		Args("a:b:c:").Rets([]string{"a:", "b:", "c:"}),
+	})
+}