text/template: implement comparison of basic types

Add eq, lt, etc. to allow one to do simple comparisons.
It's basic types only (booleans, integers, unsigned integers,
floats, complex, string) because that's easy, easy to define,
and covers the great majority of useful cases, while leaving
open the possibility of a more sweeping definition later.

{{if eq .X .Y}}X and Y are equal{{else}}X and Y are unequal{{end}}

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/13091045

1 files changed, 107 insertions, 0 deletions

diff --git a/src/pkg/text/template/exec_test.go b/src/pkg/text/template/exec_test.go
index 3d110af9cc..341c502173 100644
--- a/src/pkg/text/template/exec_test.go
+++ b/src/pkg/text/template/exec_test.go
@@ -863,3 +863,110 @@ func TestMessageForExecuteEmpty(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+type cmpTest struct {
+	expr  string
+	truth string
+	ok    bool
+}
+
+var cmpTests = []cmpTest{
+	{"eq true true", "true", true},
+	{"eq true false", "false", true},
+	{"eq 1+2i 1+2i", "true", true},
+	{"eq 1+2i 1+3i", "false", true},
+	{"eq 1.5 1.5", "true", true},
+	{"eq 1.5 2.5", "false", true},
+	{"eq 1 1", "true", true},
+	{"eq 1 2", "false", true},
+	{"eq `xy` `xy`", "true", true},
+	{"eq `xy` `xyz`", "false", true},
+	{"eq .Xuint .Xuint", "true", true},
+	{"eq .Xuint .Yuint", "false", true},
+	{"ne true true", "false", true},
+	{"ne true false", "true", true},
+	{"ne 1+2i 1+2i", "false", true},
+	{"ne 1+2i 1+3i", "true", true},
+	{"ne 1.5 1.5", "false", true},
+	{"ne 1.5 2.5", "true", true},
+	{"ne 1 1", "false", true},
+	{"ne 1 2", "true", true},
+	{"ne `xy` `xy`", "false", true},
+	{"ne `xy` `xyz`", "true", true},
+	{"ne .Xuint .Xuint", "false", true},
+	{"ne .Xuint .Yuint", "true", true},
+	{"lt 1.5 1.5", "false", true},
+	{"lt 1.5 2.5", "true", true},
+	{"lt 1 1", "false", true},
+	{"lt 1 2", "true", true},
+	{"lt `xy` `xy`", "false", true},
+	{"lt `xy` `xyz`", "true", true},
+	{"lt .Xuint .Xuint", "false", true},
+	{"lt .Xuint .Yuint", "true", true},
+	{"le 1.5 1.5", "true", true},
+	{"le 1.5 2.5", "true", true},
+	{"le 2.5 1.5", "false", true},
+	{"le 1 1", "true", true},
+	{"le 1 2", "true", true},
+	{"le 2 1", "false", true},
+	{"le `xy` `xy`", "true", true},
+	{"le `xy` `xyz`", "true", true},
+	{"le `xyz` `xy`", "false", true},
+	{"le .Xuint .Xuint", "true", true},
+	{"le .Xuint .Yuint", "true", true},
+	{"le .Yuint .Xuint", "false", true},
+	{"gt 1.5 1.5", "false", true},
+	{"gt 1.5 2.5", "false", true},
+	{"gt 1 1", "false", true},
+	{"gt 2 1", "true", true},
+	{"gt 1 2", "false", true},
+	{"gt `xy` `xy`", "false", true},
+	{"gt `xy` `xyz`", "false", true},
+	{"gt .Xuint .Xuint", "false", true},
+	{"gt .Xuint .Yuint", "false", true},
+	{"gt .Yuint .Xuint", "true", true},
+	{"ge 1.5 1.5", "true", true},
+	{"ge 1.5 2.5", "false", true},
+	{"ge 2.5 1.5", "true", true},
+	{"ge 1 1", "true", true},
+	{"ge 1 2", "false", true},
+	{"ge 2 1", "true", true},
+	{"ge `xy` `xy`", "true", true},
+	{"ge `xy` `xyz`", "false", true},
+	{"ge `xyz` `xy`", "true", true},
+	{"ge .Xuint .Xuint", "true", true},
+	{"ge .Xuint .Yuint", "false", true},
+	{"ge .Yuint .Xuint", "true", true},
+	// Errors
+	{"eq 3 4 5", "", false},     // Too many arguments.
+	{"eq `xy` 1", "", false},    // Different types.
+	{"lt true true", "", false}, // Unordered types.
+	{"lt 1+0i 1+0i", "", false}, // Unordered types.
+}
+
+func TestComparison(t *testing.T) {
+	b := new(bytes.Buffer)
+	var cmpStruct = struct {
+		Xuint, Yuint uint
+	}{3, 4}
+	for _, test := range cmpTests {
+		text := fmt.Sprintf("{{if %s}}true{{else}}false{{end}}", test.expr)
+		tmpl, err := New("empty").Parse(text)
+		if err != nil {
+			t.Fatal(err)
+		}
+		b.Reset()
+		err = tmpl.Execute(b, &cmpStruct)
+		if test.ok && err != nil {
+			t.Errorf("%s errored incorrectly: %s", test.expr, err)
+			continue
+		}
+		if !test.ok && err == nil {
+			t.Errorf("%s did not error")
+			continue
+		}
+		if b.String() != test.truth {
+			t.Errorf("%s: want %s; got %s", test.expr, test.truth, b.String())
+		}
+	}
+}