fix(config): Handle escaping and quotation correctly (#13675)

config/config.go

@@ -807,8 +807,8 @@ func removeComments(contents []byte) ([]byte, error) {
 	tomlReader := bytes.NewReader(contents)
 
 	// Initialize variables for tracking state
-	var inQuote, inComment bool
+	var inQuote, inComment, escaped bool
-	var quoteChar, prevChar byte
+	var quoteChar byte
 
 	// Initialize buffer for modified TOML data
 	var output bytes.Buffer
@@ -825,6 +825,11 @@ func removeComments(contents []byte) ([]byte, error) {
 		}
 		char := buf[0]
 
+		// Toggle the escaped state at backslash to we have true every odd occurrence.
+		if char == '\\' {
+			escaped = !escaped
+		}
+
 		if inComment {
 			// If we're currently in a comment, check if this character ends the comment
 			if char == '\n' {
@@ -834,26 +839,30 @@ func removeComments(contents []byte) ([]byte, error) {
 			}
 		} else if inQuote {
 			// If we're currently in a quote, check if this character ends the quote
-			if char == quoteChar && prevChar != '\\' {
+			if char == quoteChar && !escaped {
 				// End of quote, we're no longer in a quote
 				inQuote = false
 			}
 			output.WriteByte(char)
 		} else {
 			// Not in a comment or a quote
-			if char == '"' || char == '\'' {
+			if (char == '"' || char == '\'') && !escaped {
 				// Start of quote
 				inQuote = true
 				quoteChar = char
 				output.WriteByte(char)
-			} else if char == '#' {
+			} else if char == '#' && !escaped {
 				// Start of comment
 				inComment = true
 			} else {
 				// Not a comment or a quote, just output the character
 				output.WriteByte(char)
 			}
-			prevChar = char
+		}
+
+		// Reset escaping if any other character occurred
+		if char != '\\' {
+			escaped = false
 		}
 	}
 	return output.Bytes(), nil

config/internal_test.go

@@ -302,6 +302,55 @@ func TestEnvironmentSubstitutionNewBehavior(t *testing.T) {
 	}
 }
 
+func TestParseConfig(t *testing.T) {
+	tests := []struct {
+		name     string
+		setEnv   func(*testing.T)
+		contents string
+		expected string
+		errmsg   string
+	}{
+		{
+			name: "empty var name",
+			contents: `
+# Environment variables can be used anywhere in this config file, simply surround
+# them with ${}. For strings the variable must be within quotes (ie, "${STR_VAR}"),
+# for numbers and booleans they should be plain (ie, ${INT_VAR}, ${BOOL_VAR})Should output ${NOT_SET:-${FALLBACK}}
+`,
+			expected: "\n\n\n\n",
+		},
+		{
+			name: "comment in command (issue #13643)",
+			contents: `
+			[[inputs.exec]]
+			  commands = ["echo \"abc#def\""]
+			`,
+			expected: `
+			[[inputs.exec]]
+			  commands = ["echo \"abc#def\""]
+			`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.setEnv != nil {
+				tt.setEnv(t)
+			}
+			tbl, err := parseConfig([]byte(tt.contents))
+			if tt.errmsg != "" {
+				require.ErrorContains(t, err, tt.errmsg)
+				return
+			}
+
+			require.NoError(t, err)
+			if len(tt.expected) > 0 {
+				require.EqualValues(t, tt.expected, string(tbl.Data))
+			}
+		})
+	}
+}
+
 func TestURLRetries3Fails(t *testing.T) {
 	httpLoadConfigRetryInterval = 0 * time.Second
 	responseCounter := 0