text/template: don't evaluate '.' as a float64

When using a '.' constant literal as a reflect.Value variadic argument,
idealConstant would incorrectly result in a float64. This is because
rune literals can be represented as a float64, and contain a period,
which tricked the logic into thinking the literal must have been a
floating point number.

This also happened with other characters that can be part of a floating
point number, such as 'e' or 'P'.

To fix these edge cases, exit the case sooner if the literal was a rune,
since that should always go to the int case instead.

Finally, add test cases that verify that they behave properly. These
would error before, since eq would receive a mix of int and float64,
which aren't comparable.

Fixes #34483.

Change-Id: Icfcb7803bfa0cf317a1d1adacacad3d69a57eb42
Reviewed-on: https://go-review.googlesource.com/c/go/+/196808
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tom Payne <tom@airmap.com>
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index 7f2305ace0..f24a59e549 100644
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -663,6 +663,12 @@ var execTests = []execTest{
 	{"bug17c", "{{len .NonEmptyInterfacePtS}}", "2", tVal, true},
 	{"bug17d", "{{index .NonEmptyInterfacePtS 0}}", "a", tVal, true},
 	{"bug17e", "{{range .NonEmptyInterfacePtS}}-{{.}}-{{end}}", "-a--b-", tVal, true},
+
+	// More variadic function corner cases. Some runes would get evaluated
+	// as constant floats instead of ints. Issue 34483.
+	{"bug18a", "{{eq . '.'}}", "true", '.', true},
+	{"bug18b", "{{eq . 'e'}}", "true", 'e', true},
+	{"bug18c", "{{eq . 'P'}}", "true", 'P', true},
 }
 
 func zeroArgs() string {