Improve variable substitution, fixes #89

lib/chezmoi/autotemplate.go

@@ -1,7 +1,6 @@
 package chezmoi
 
 import (
-	"regexp"
 	"sort"
 	"strings"
 )
@@ -45,15 +44,34 @@ func extractVariables(variables []templateVariable, parent []string, data map[st
 func autoTemplate(contents []byte, data map[string]interface{}) ([]byte, error) {
 	// FIXME this naive approach will generate incorrect templates if the
 	// variable names match variable values
+	// FIXME the algorithm here is probably O(N^2), we can do better
 	variables := extractVariables(nil, nil, data)
 	sort.Sort(sort.Reverse(byValueLength(variables)))
 	contentsStr := string(contents)
 	for _, variable := range variables {
-		valueRegexp, err := regexp.Compile(`\b` + regexp.QuoteMeta(variable.value) + `\b`)
-		if err != nil {
-			return nil, err
+		index := strings.Index(contentsStr, variable.value)
+		for index != -1 && index != len(contentsStr) {
+			if !inWord(contentsStr, index) && !inWord(contentsStr, index+len(variable.value)) {
+				// Replace variable.value which is on word boundaries at both
+				// ends.
+				replacement := "{{ ." + variable.name + " }}"
+				contentsStr = contentsStr[:index] + replacement + contentsStr[index+len(variable.value):]
+				index += len(replacement)
+			} else {
+				// Otherwise, keep looking. Consume at least one byte so we
+				// make progress.
+				index++
+			}
+			// Look for the next occurrence of variable.value.
+			j := strings.Index(contentsStr[index:], variable.value)
+			if j == -1 {
+				// No more occurrences found, so terminate the loop.
+				break
+			} else {
+				// Advance to the next occurrence.
+				index += j
+			}
 		}
-		contentsStr = valueRegexp.ReplaceAllString(contentsStr, "{{ ."+variable.name+" }}")
 	}
 	return []byte(contentsStr), nil
 }

lib/chezmoi/autotemplate_test.go

@@ -54,17 +54,62 @@ func TestAutoTemplate(t *testing.T) {
 			},
 			wantStr: "darwinian evolution", // not "{{ .os }}ian evolution"
 		},
-		/*
-			// FIXME this test currently fails because we match on word
-			// boundaries and ^/ is not a word boundary.
-			{
-				contentsStr: "/home/user",
-				data: map[string]interface{}{
-					"homedir": "/home/user",
-				},
-				wantStr: "{{ .homedir }}",
+		{
+			name:        "longest_match_first",
+			contentsStr: "/home/user",
+			data: map[string]interface{}{
+				"homedir": "/home/user",
+			},
+			wantStr: "{{ .homedir }}",
+		},
+		{
+			name:        "longest_match_first_prefix",
+			contentsStr: "HOME=/home/user",
+			data: map[string]interface{}{
+				"homedir": "/home/user",
+			},
+			wantStr: "HOME={{ .homedir }}",
+		},
+		{
+			name:        "longest_match_first_suffix",
+			contentsStr: "/home/user/something",
+			data: map[string]interface{}{
+				"homedir": "/home/user",
+			},
+			wantStr: "{{ .homedir }}/something",
+		},
+		{
+			name:        "longest_match_first_prefix_and_suffix",
+			contentsStr: "HOME=/home/user/something",
+			data: map[string]interface{}{
+				"homedir": "/home/user",
+			},
+			wantStr: "HOME={{ .homedir }}/something",
+		},
+		{
+			name:        "words_only",
+			contentsStr: "aaa aa a aa aaa aa a aa aaa",
+			data: map[string]interface{}{
+				"alpha": "a",
+			},
+			wantStr: "aaa aa {{ .alpha }} aa aaa aa {{ .alpha }} aa aaa",
+		},
+		{
+			name:        "words_only_2",
+			contentsStr: "aaa aa a aa aaa aa a aa aaa",
+			data: map[string]interface{}{
+				"alpha": "aa",
 			},
-		*/
+			wantStr: "aaa {{ .alpha }} a {{ .alpha }} aaa {{ .alpha }} a {{ .alpha }} aaa",
+		},
+		{
+			name:        "words_only_3",
+			contentsStr: "aaa aa a aa aaa aa a aa aaa",
+			data: map[string]interface{}{
+				"alpha": "aaa",
+			},
+			wantStr: "{{ .alpha }} aa a aa {{ .alpha }} aa a aa {{ .alpha }}",
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			got, gotErr := autoTemplate([]byte(tc.contentsStr), tc.data)