Add export and install scripts for fish shell

Closes https://github.com/espressif/esp-idf/issues/4459
Merges https://github.com/espressif/esp-idf/pull/4944

export.fish

@@ -0,0 +1,74 @@
+# This script should be sourced, not executed.
+
+function idf_export_main
+    # The file doesn't have executable permissions, so this shouldn't really happen.
+    # Doing this in case someone tries to chmod +x it and execute...
+    set cmd (status current-command)
+    if test $cmd != source -a $cmd != .
+        echo "his script should be sourced, not executed:"
+        echo . (realpath (status --current-filename)/..)
+        return 1
+    end
+
+    if not set -q IDF_PATH
+        echo "IDF_PATH must be set before sourcing this script"
+        return 1
+    end
+
+    set oldpath = $PATH
+
+    echo "Adding ESP-IDF tools to PATH..."
+    # Call idf_tools.py to export tool paths
+    set -x IDF_TOOLS_EXPORT_CMD "$IDF_PATH"/export.fish
+    set -x IDF_TOOLS_INSTALL_CMD "$IDF_PATH"/install.fish
+    set idf_exports ("$IDF_PATH"/tools/idf_tools.py export) || return 1
+    eval "$idf_exports"
+
+    echo "Checking if Python packages are up to date..."
+    python "$IDF_PATH"/tools/check_python_dependencies.py || return 1
+
+    # Allow calling some IDF python tools without specifying the full path
+    # "$IDF_PATH"/tools is already added by 'idf_tools.py export'
+    set IDF_ADD_PATHS_EXTRAS "$IDF_PATH"/components/esptool_py/esptool
+    set IDF_ADD_PATHS_EXTRAS "$IDF_ADD_PATHS_EXTRAS":"$IDF_PATH"/components/espcoredump
+    set IDF_ADD_PATHS_EXTRAS "$IDF_ADD_PATHS_EXTRAS":"$IDF_PATH"/components/partition_table/
+    set -x PATH "$IDF_ADD_PATHS_EXTRAS":"$PATH"
+
+    set added_path_variables
+    for entry in $PATH;
+        if not contains $entry $oldpath
+            set -a added_path_variables $entry
+        end
+    end
+    if set -q added_path_variables[1]
+        echo "Added the following directories to PATH:"
+        for entry in $added_path_variables;
+            echo $entry
+        end
+    else
+        echo "All paths are already set."
+    end
+
+    # Clean up
+    set -e added_path_variables
+    set -e cmd
+    set -e old_path
+    set -e paths
+    set -e path_prefix
+    set -e path_entry
+    set -e IDF_ADD_PATHS_EXTRAS
+    set -e idf_exports
+
+    # Not unsetting IDF_PYTHON_ENV_PATH, it can be used by IDF build system
+    # to check whether we are using a private Python environment
+
+    echo "Done! You can now compile ESP-IDF projects."
+    echo "Go to the project directory and run:"
+    echo ""
+    echo "  idf.py build"
+    echo ""
+end
+
+idf_export_main
+
+set -e idf_export_main

install.fish

@@ -0,0 +1,16 @@
+#!/usr/bin/env fish
+
+set basedir (realpath (status --current-filename)/..)
+
+set -x IDF_PATH $basedir
+
+echo "Installing ESP-IDF tools"
+"$IDF_PATH"/tools/idf_tools.py install
+
+echo "Installing Python environment and packages"
+"$IDF_PATH"/tools/idf_tools.py install-python-env
+
+echo "All done! You can now run:"
+echo ""
+echo "  . "$basedir"/export.fish"
+echo ""