feat: exclude lines from processing

README.md

@@ -77,6 +77,25 @@ const myVariable = 99
 const os = process.platform === 'darwin' ? 'OSXy' /* c8 ignore next */ : 'Windowsy' 
 ```
 
+## Excluding Lines
+
+Sometimes you might find yourself wanting to exclude lines
+in your application (for example, perhaps you have your unit tests inside of a file
+you wish to check coverage of, but
+you don't want to include the tests in the report).
+
+To exclude lines, use the special comments `/* c8 exclude start */` and `/* c8 exclude stop */`.
+
+### Excluding all lines until told
+
+```js
+/* c8 exclude start */
+function excludeMe() {
+  // ...
+}
+/* c8 exclude stop */
+```
+
 ## Testing
 
 To execute tests, simply run:

lib/source.js

@@ -16,15 +16,22 @@ module.exports = class CovSource {
     let position = 0
     let ignoreCount = 0
     let ignoreAll = false
+    let excludeAll = false
     for (const [i, lineStr] of source.split(/(?<=\r?\n)/u).entries()) {
       const line = new CovLine(i + 1, position, lineStr)
+      const excludeToken = this._parseExclude(lineStr)
+      if (excludeToken) {
+        excludeAll = excludeToken?.start
+      }
       if (ignoreCount > 0) {
         line.ignore = true
         ignoreCount--
       } else if (ignoreAll) {
         line.ignore = true
       }
-      this.lines.push(line)
+      if (!excludeAll && !excludeToken?.stop) {
+        this.lines.push(line)
+      }
       position += lineStr.length
 
       const ignoreToken = this._parseIgnore(lineStr)
@@ -73,6 +80,21 @@ module.exports = class CovSource {
     }
   }
 
+  /**
+ * Parses for comments:
+ *    c8 exclude start
+ *    c8 exclude stop
+ * @param {string} lineStr
+ * @return {{start?: boolean, stop?: boolean}|undefined}
+ */
+  _parseExclude (lineStr) {
+    const testExcludeStartStop = lineStr.match(/\/\* c8 exclude (?<mode>start|stop)/)
+    if (testExcludeStartStop) {
+      if (testExcludeStartStop.groups.mode === 'start') return { start: true }
+      if (testExcludeStartStop.groups.mode === 'stop') return { stop: true }
+    }
+  }
+
   // given a start column and end column in absolute offsets within
   // a source file (0 - EOF), returns the relative line column positions.
   offsetToOriginalRelative (sourceMap, startCol, endCol) {