setup.sh: tidy some shell-fu in order to detect 'flutter' and resolve 'dart' better (#10059)

* setup.sh: tidy some shell-fu in order to detect flutter and resolve dart better

* Update tool/ci/setup.sh

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

tool/ci/setup.sh

diff --git a/tool/ci/setup.sh b/tool/ci/setup.sh
index fb0149e..fab26a7 100755
--- a/tool/ci/setup.sh
+++ b/tool/ci/setup.sh
@@ -10,25 +10,16 @@
 export SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
 export DEVTOOLS_DIR=$SCRIPT_DIR/../..
 
-# In GitBash on Windows, we have to call flutter.bat so we alias them in this
-# script to call the correct one based on the OS.
-function flutter {
-    if [[ $RUNNER_OS == "Windows" ]]; then
-        command flutter.bat "$@"
-    else
-        command flutter "$@"
-    fi
-}
-export -f flutter
-
 # Determine the Flutter SDK to use:
 # * If `DEVTOOLS_TOOL_FLUTTER_FROM_PATH` is "true", then discover from `PATH`.
 # * If `./tool/flutter-sdk` (a directory) exists, then use that.
 if [ "$DEVTOOLS_TOOL_FLUTTER_FROM_PATH" = "true" ]; then
-    if command -v flutter &> /dev/null; then
-        FLUTTER_EXE="$(command -v flutter)"
-    elif command -v flutter.bat &> /dev/null; then
-        FLUTTER_EXE="$(command -v flutter.bat)"
+    # Use `type -P` instead of `command -v` so we resolve an executable file on
+    # PATH rather than a shell function or alias.
+    if type -P flutter &> /dev/null; then
+        FLUTTER_EXE="$(type -P flutter)"
+    elif type -P flutter.bat &> /dev/null; then
+        FLUTTER_EXE="$(type -P flutter.bat)"
     else
         echo "DEVTOOLS_TOOL_FLUTTER_FROM_PATH is set to true, but flutter was not found on PATH"
         exit 1
@@ -50,6 +41,17 @@
 # inopportune times.
 export PATH="$FLUTTER_DIR/bin/cache/dart-sdk/bin:$FLUTTER_DIR/bin:`pwd`/bin:$PATH"
 
+# In GitBash on Windows, we have to call flutter.bat so we alias them in this
+# script to call the correct one based on the OS.
+function flutter {
+    if [[ "$RUNNER_OS" == "Windows" || "$OSTYPE" == "msys" || "$OSTYPE" == "cygwin" ]]; then
+        command flutter.bat "$@"
+    else
+        command flutter "$@"
+    fi
+}
+export -f flutter
+
 # Look up the latest flutter candidate (this is the latest flutter version in g3)
 # TODO(https://github.com/flutter/devtools/issues/4591): re-write this script as a
 # shell script so we won't have to incurr the cost of building flutter tool twice.