From 8d7c5e8313fe348a4682af5877ca570ebd030343 Mon Sep 17 00:00:00 2001
From: Sebastian Ehlert <28669218+awvwgk@users.noreply.github.com>
Date: Sun, 6 Dec 2020 11:08:29 +0100
Subject: Try to use local install path with fallback to platform defaults

- use $HOME/.local as user prefix on Unix platforms (fallback is /usr/local)
- use %APPDATA%\local as user prefix on Windows (fallback is C:\)
---
 fpm/src/fpm/installer.f90  | 36 ++++++++++++++++++++++++++++++------
 fpm/src/fpm_filesystem.f90 | 23 ++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/fpm/src/fpm/installer.f90 b/fpm/src/fpm/installer.f90
index ddfc77b..d01bd27 100644
--- a/fpm/src/fpm/installer.f90
+++ b/fpm/src/fpm/installer.f90
@@ -7,7 +7,8 @@ module fpm_installer
   use, intrinsic :: iso_fortran_env, only : output_unit
   use fpm_environment, only : get_os_type, os_is_unix
   use fpm_error, only : error_t, fatal_error
-  use fpm_filesystem, only : join_path, mkdir, exists, unix_path, windows_path
+  use fpm_filesystem, only : join_path, mkdir, exists, unix_path, windows_path, &
+    env_variable
   implicit none
   private
 
@@ -109,11 +110,7 @@ contains
     if (present(prefix)) then
       self%prefix = prefix
     else
-      if (os_is_unix(self%os)) then
-        self%prefix = default_prefix_unix
-      else
-        self%prefix = default_prefix_win
-      end if
+      call set_default_prefix(self%prefix, self%os)
     end if
 
     if (present(bindir)) then
@@ -136,6 +133,33 @@ contains
 
   end subroutine new_installer
 
+  !> Set the default prefix for the installation
+  subroutine set_default_prefix(prefix, os)
+    !> Installation prefix
+    character(len=:), allocatable :: prefix
+    !> Platform identifier
+    integer, intent(in), optional :: os
+
+    character(len=:), allocatable :: home
+
+    if (os_is_unix(os)) then
+      call env_variable(home, "HOME")
+      if (allocated(home)) then
+        prefix = join_path(home, ".local")
+      else
+        prefix = default_prefix_unix
+      end if
+    else
+      call env_variable(home, "APPDATA")
+      if (allocated(home)) then
+        prefix = join_path(home, "local")
+      else
+        prefix = default_prefix_win
+      end if
+    end if
+
+  end subroutine set_default_prefix
+
   !> Install an executable in its correct subdirectory
   subroutine install_executable(self, executable, error)
     !> Instance of the installer
diff --git a/fpm/src/fpm_filesystem.f90 b/fpm/src/fpm_filesystem.f90
index 433a75b..f221917 100644
--- a/fpm/src/fpm_filesystem.f90
+++ b/fpm/src/fpm_filesystem.f90
@@ -5,7 +5,7 @@ module fpm_filesystem
     use fpm_strings, only: f_string, string_t, split
     implicit none
     private
-    public :: basename, canon_path, dirname, is_dir, join_path, number_of_rows, read_lines, list_files,&
+    public :: basename, canon_path, dirname, is_dir, join_path, number_of_rows, read_lines, list_files, env_variable, &
             mkdir, exists, get_temp_filename, windows_path, unix_path, getline, delete_file
 
     integer, parameter :: LINE_BUFFER_LEN = 1000
@@ -13,6 +13,27 @@ module fpm_filesystem
 contains
 
 
+subroutine env_variable(var, name)
+   character(len=:), allocatable, intent(out) :: var
+   character(len=*), intent(in) :: name
+   integer :: length, stat
+
+   call get_environment_variable(name, length=length, status=stat)
+   if (stat /= 0) return
+
+   allocate(character(len=length) :: var)
+
+   if (length > 0) then
+      call get_environment_variable(name, var, status=stat)
+      if (stat /= 0) then
+         deallocate(var)
+         return
+      end if
+   end if
+
+end subroutine env_variable
+
+
 function basename(path,suffix) result (base)
     ! Extract filename from path with/without suffix
     !
-- 
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