Add a bin/flutter-dev script, for running the flutter command-line tool from source (#153599)

Not so long ago I remember a very informal conversation that went something like this:

> @matanlurey: I wish I could pass `--dev` or something to `flutter` to run from source.
>
> @christopherfujino: I get what you want, but I don't want to overload the tool with more dev-only things. I would consider a script like `flutter-dev` that does that thing, though.
>
> @matanlurey: Cool, I might send a PR!

So uh, here it is 6-9 months later. Suggestions welcome.

bin/flutter-dev

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# Copyright 2014 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+set -e
+
+# This is a helper script for development purposes. It runs the Flutter tool
+# from source code directly, without using the prebuilt snapshot. This is
+# useful for development, as it allows you to make changes to the tool and see
+# the effects immediately, but is much slower than using the prebuilt snapshot.
+
+# To debug the tool, you can uncomment the following lines to enable debug
+# mode and set an observatory port:
+# FLUTTER_TOOL_ARGS="--enable-asserts $FLUTTER_TOOL_ARGS"
+# FLUTTER_TOOL_ARGS="$FLUTTER_TOOL_ARGS --observe=65432"
+
+# Needed because if it is set, cd may print the path it changed to.
+unset CDPATH
+
+# On Mac OS, readlink -f doesn't work, so follow_links traverses the path one
+# link at a time, and then cds into the link destination and find out where it
+# ends up.
+#
+# The returned filesystem path must be a format usable by Dart's URI parser,
+# since the Dart command line tool treats its argument as a file URI, not a
+# filename. For instance, multiple consecutive slashes should be reduced to a
+# single slash, since double-slashes indicate a URI "authority", and these are
+# supposed to be filenames. There is an edge case where this will return
+# multiple slashes: when the input resolves to the root directory. However, if
+# that were the case, we wouldn't be running this shell, so we don't do anything
+# about it.
+#
+# The function is enclosed in a subshell to avoid changing the working directory
+# of the caller.
+function follow_links() (
+  cd -P "$(dirname -- "$1")"
+  file="$PWD/$(basename -- "$1")"
+  while [[ -h "$file" ]]; do
+    cd -P "$(dirname -- "$file")"
+    file="$(readlink -- "$file")"
+    cd -P "$(dirname -- "$file")"
+    file="$PWD/$(basename -- "$file")"
+  done
+  echo "$file"
+)
+
+# Lookup the parent directory of the script (../), the Flutter SDK root.
+PROG_NAME="$(follow_links "${BASH_SOURCE[0]}")"
+BIN_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"
+SHARED_NAME="$BIN_DIR/internal/shared.sh"
+FLUTTER_ROOT="$(cd "$BIN_DIR/.." ; pwd -P)"
+
+# To define `shared::execute()` function
+source "$SHARED_NAME"
+
+# Run the Flutter tool directly without using the cached snapshot.
+shared::execute "$@"

bin/internal/shared.sh

@@ -143,7 +143,7 @@ function upgrade_flutter () (
     touch "$FLUTTER_ROOT/bin/cache/.dartignore"
     "$FLUTTER_ROOT/bin/internal/update_dart_sdk.sh"
 
-    if [[ "$BIN_NAME" == 'dart' ]]; then
+    if [[ "$BIN_NAME" == 'dart' || "$BIN_NAME" == 'flutter-dev' ]]; then
       # Don't try to build tool
       return
     fi
@@ -259,6 +259,11 @@ function shared::execute() {
       # considered as separate space-separated args.
       exec "$DART" --disable-dart-dev --packages="$FLUTTER_TOOLS_DIR/.dart_tool/package_config.json" $FLUTTER_TOOL_ARGS "$SNAPSHOT_PATH" "$@"
       ;;
+    flutter-dev*)
+      # FLUTTER_TOOL_ARGS aren't quoted below, because it is meant to be
+      # considered as separate space-separated args.
+      exec "$DART" --packages="$FLUTTER_TOOLS_DIR/.dart_tool/package_config.json" $FLUTTER_TOOL_ARGS "$SCRIPT_PATH" "$@"
+      ;;
     dart*)
       exec "$DART" "$@"
       ;;

dev/bots/analyze.dart

@@ -2216,6 +2216,7 @@ Future<CommandResult> _runFlutterAnalyze(String workingDirectory, {
 const Set<String> kExecutableAllowlist = <String>{
   'bin/dart',
   'bin/flutter',
+  'bin/flutter-dev',
   'bin/internal/update_dart_sdk.sh',
 
   'dev/bots/accept_android_sdk_licenses.sh',

packages/flutter_tools/README.md

@@ -26,6 +26,11 @@ $ dart bin/flutter_tools.dart
 ```
 followed by command-line arguments, as usual.
 
+As a convenience, you can also use the `bin/flutter-dev` script:
+```shell
+# Assuming flutter/bin is on your PATH
+$ flutter-dev
+```
 
 ### Running the analyzer