search: empty string values for attr and tag predicates

Fixes issue_461

Change-Id: I94cba8be70f30eca456d990ba4f4db2618b24553

pkg/search/expr_test.go

@@ -572,9 +572,9 @@ var parseExpTests = []parserTestCase{
 		in: "attr:foo:",
 		want: &Constraint{
 			Permanode: &PermanodeConstraint{
-				Attr:       "foo",
-				Value:      "",
-				SkipHidden: true,
+				Attr:         "foo",
+				ValueMatches: &StringConstraint{Empty: true},
+				SkipHidden:   true,
 			},
 		},
 	},

pkg/search/predicate.go

@@ -238,13 +238,7 @@ func (a attribute) Description() string {
 }
 
 func (a attribute) Predicate(ctx *context.Context, args []string) (*Constraint, error) {
-	c := &Constraint{
-		Permanode: &PermanodeConstraint{
-			Attr:       args[0],
-			SkipHidden: true,
-			Value:      args[1],
-		},
-	}
+	c := attrConst(args[0], args[1])
 	if strings.HasPrefix(args[1], "~") {
 		// Substring. Hack. Figure out better way to do this.
 		c.Permanode.Value = ""
@@ -321,14 +315,7 @@ func (t tag) Description() string {
 }
 
 func (t tag) Predicate(ctx *context.Context, args []string) (*Constraint, error) {
-	c := &Constraint{
-		Permanode: &PermanodeConstraint{
-			Attr:       "tag",
-			SkipHidden: true,
-			Value:      args[0],
-		},
-	}
-	return c, nil
+	return attrConst("tag", args[0]), nil
 }
 
 type title struct {
@@ -571,6 +558,21 @@ func (h hasLocation) Predicate(ctx *context.Context, args []string) (*Constraint
 
 // Helpers
 
+func attrConst(attr, val string) *Constraint {
+	c := &Constraint{
+		Permanode: &PermanodeConstraint{
+			Attr:       attr,
+			SkipHidden: true,
+		},
+	}
+	if val == "" {
+		c.Permanode.ValueMatches = &StringConstraint{Empty: true}
+	} else {
+		c.Permanode.Value = val
+	}
+	return c
+}
+
 func permOfFile(fc *FileConstraint) *Constraint {
 	return &Constraint{
 		Permanode: &PermanodeConstraint{

pkg/search/predicate_test.go

@@ -190,6 +190,18 @@ var keywordTests = []keywordTestcase{
 		want:   attrfoobarC,
 	},
 
+	{
+		object: newAttribute(),
+		args:   []string{"foo", ""},
+		want: &Constraint{
+			Permanode: &PermanodeConstraint{
+				Attr:         "foo",
+				ValueMatches: &StringConstraint{Empty: true},
+				SkipHidden:   true,
+			},
+		},
+	},
+
 	{
 		object: newAttribute(),
 		args:   []string{"foo", "~bar"},
@@ -255,6 +267,31 @@ var keywordTests = []keywordTestcase{
 		},
 	},
 
+	{
+		object: newTag(),
+		args:   []string{""},
+		want: &Constraint{
+			Permanode: &PermanodeConstraint{
+				Attr:         "tag",
+				ValueMatches: &StringConstraint{Empty: true},
+				SkipHidden:   true,
+			},
+		},
+	},
+
+	{
+		object: newTitle(),
+		args:   []string{""},
+		want: &Constraint{
+			Permanode: &PermanodeConstraint{
+				Attr:       "title",
+				SkipHidden: true,
+				ValueMatches: &StringConstraint{
+					CaseInsensitive: true,
+				},
+			}},
+	},
+
 	{
 		object: newTitle(),
 		args:   []string{"foo"},

pkg/search/query.go

@@ -225,7 +225,7 @@ func (q *SearchQuery) checkValid(ctx *context.Context) (sq *SearchQuery, err err
 				return nil, fmt.Errorf("Error parsing search expression %q: %v", expr, err)
 			}
 			if err := sq.Constraint.checkValid(); err != nil {
-				log.Fatalf("Internal error: parseExpression(%q) returned invalid constraint: %v", expr, err)
+				return nil, fmt.Errorf("Internal error: parseExpression(%q) returned invalid constraint: %v", expr, err)
 			}
 			return sq, nil
 		}