fix null check errors

src/cli/parse-flags.ts

@@ -119,6 +119,9 @@ const parseCLITerm = (flags: ConfigFlags, args: string[]) => {
   // pull off the first arg from the argument array
   const arg = args.shift();
 
+  // array is empty, we're done!
+  if (arg === undefined) return;
+
   // EqualsArg → "--" ArgName "=" CLIValue ;
   if (arg.startsWith('--') && arg.includes('=')) {
     // we're dealing with an EqualsArg, we have a special helper for that
@@ -216,9 +219,7 @@ const normalizeFlagName = (flagName: string): string => {
  * @param value the raw value to be set onto the config flags object
  */
 const setCLIArg = (flags: ConfigFlags, rawArg: string, normalizedArg: string, value: CLIValueResult) => {
-  if (CLI_FLAG_ALIASES[normalizedArg] !== undefined) {
-    normalizedArg = CLI_FLAG_ALIASES[normalizedArg];
-  }
+  normalizedArg = dereferenceAlias(normalizedArg);
 
   if (readOnlyArrayHasStringMember(BOOLEAN_CLI_FLAGS, normalizedArg)) {
     flags[normalizedArg] =
@@ -247,9 +248,16 @@ const setCLIArg = (flags: ConfigFlags, rawArg: string, normalizedArg: string, va
         flags[normalizedArg] = [];
       }
 
-      flags[normalizedArg].push(value);
-      flags.knownArgs.push(rawArg);
-      flags.knownArgs.push(value);
+      const targetArray = flags[normalizedArg];
+      // this is irritating, but TS doesn't know that the `!Array.isArray`
+      // check above guarantees we have an array to work with here, and it
+      // doesn't want to narrow the type of `flags[normalizedArg]`, so we need
+      // to grab a reference to that array and then `Array.isArray` that. Bah!
+      if (Array.isArray(targetArray)) {
+        targetArray.push(value);
+        flags.knownArgs.push(rawArg);
+        flags.knownArgs.push(value);
+      }
     } else {
       throwCLIParsingError(rawArg, 'expected a string argument but received nothing');
     }
@@ -361,12 +369,16 @@ const parseCLIValue = (args: string[]): CLIValueResult => {
   if (args[0] === undefined) {
     return Empty;
   }
+
   // all we're concerned with here is that it does not start with `"-"`,
   // which would indicate it should be parsed as a CLI flag and not a value.
   if (!args[0].startsWith('-')) {
     // It's not a flag, so we return the value and defer any specific parsing
     // until later on.
-    return args.shift();
+    const value = args.shift();
+    if (typeof value === 'string') {
+      return value;
+    }
   }
   return Empty;
 };
@@ -441,3 +453,23 @@ const throwCLIParsingError = (flag: string, message: string) => {
 const throwNumberParsingError = (flag: string, value: string) => {
   throwCLIParsingError(flag, `expected a number but received "${value}"`);
 };
+
+/**
+ * A little helper to 'dereference' a flag alias, which if you squint a little
+ * you can think of like a pointer to a full flag name. This 'c' is like a
+ * pointer to 'config', so here we're doing something like `*c`. Of course, this
+ * being JS, this is just a metaphor!
+ *
+ * If no 'dereference' is found for the possible alias we just return the passed string unmodified.
+ *
+ * @param maybeAlias a string which _could_ be an alias to a full flag name
+ * @returns the full aliased flag name, if found, or the passed string if not
+ */
+const dereferenceAlias = (maybeAlias: string): string => {
+  const possibleDereference = CLI_FLAG_ALIASES[maybeAlias];
+
+  if (typeof possibleDereference === 'string') {
+    return possibleDereference;
+  }
+  return maybeAlias;
+};