Fix infinite loop on single match

If there's a single entry in the collection of matches, our huffman
implementation will return an empty label. That results in an infinite
loop when rendering because we attempt to match empy input to an empty
label.

Resolve this by handling the single match case separately.

Fixes #38

CHANGELOG.md

@@ -10,6 +10,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Change default action to `tmux load-buffer -`. This eliminates risk of
   hitting ARG_MAX with `set-buffer`--however unlikely that was.
 
+### Fixed
+- ([#38]): Fix infinite loop when there's a single match.
+
+  ([#38]): https://github.com/abhinav/tmux-fastcopy/issues/38
+
 ## 0.4.0 - 2021-09-06
 Highlight: The minimum required version of Tmux was lowered to 3.0.
 

internal/huffman/huffman.go

@@ -25,8 +25,13 @@ func Label(alphabetSize int, freqs []int) (labels [][]int) {
 		panic("alphabet must have at least two elements")
 	}
 
-	if len(freqs) == 0 {
+	switch len(freqs) {
+	case 0:
 		return nil
+	case 1:
+		// special-case: If there's only one item, create a single
+		// letter alabel.
+		return [][]int{{0}}
 	}
 
 	// Fill the heap with leaf nodes for the user-provided elements.

internal/huffman/huffman_test.go

@@ -70,6 +70,15 @@ func TestLabel(t *testing.T) {
 		alphabet *alphabet
 		items    []item
 	}{
+		{
+			alphabet: _ab,
+		},
+		{
+			alphabet: _ab,
+			items: []item{
+				{1, "a"},
+			},
+		},
 		{
 			alphabet: _ab,
 			items: []item{
@@ -149,6 +158,10 @@ func assertLabelInvariants(t *testing.T, numItems int, labels []string) bool {
 	// 2) There must be no duplicates.
 	var seen []string
 	for _, label := range labels {
+		if !assert.NotEmpty(t, label, "label with %d items must not be empty", numItems) {
+			return false
+		}
+
 		if !assert.NotContains(t, seen, label, "duplicate label %q", label) {
 			return false
 		}