From cf49f39f94c6da95842c8505117e7714ee016f41 Mon Sep 17 00:00:00 2001
From: Laurence Kedward <laurence.kedward@bristol.ac.uk>
Date: Wed, 6 Jan 2021 17:59:20 +0000
Subject: Add: string_len_trim to check for empty source files (#335)

Fixes performance regression from 33ad2ce. Don't use string_cat for checking for empty source files.
---
 fpm/src/fpm_source_parsing.f90 |  6 +++---
 fpm/src/fpm_strings.f90        | 19 ++++++++++++++++++-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/fpm/src/fpm_source_parsing.f90 b/fpm/src/fpm_source_parsing.f90
index f81555d..db271ed 100644
--- a/fpm/src/fpm_source_parsing.f90
+++ b/fpm/src/fpm_source_parsing.f90
@@ -16,7 +16,7 @@
 !>
 module fpm_source_parsing
 use fpm_error, only: error_t, file_parse_error, fatal_error
-use fpm_strings, only: string_t, string_cat, split, lower, str_ends_with, fnv_1a
+use fpm_strings, only: string_t, string_cat, len_trim, split, lower, str_ends_with, fnv_1a
 use fpm_model, only: srcfile_t, &
                     FPM_UNIT_UNKNOWN, FPM_UNIT_PROGRAM, FPM_UNIT_MODULE, &
                     FPM_UNIT_SUBMODULE, FPM_UNIT_SUBPROGRAM, &
@@ -87,7 +87,7 @@ function parse_f_source(f_filename,error) result(f_source)
     close(fh)
 
     ! Ignore empty files, returned as FPM_UNIT_UNKNOW
-    if (len_trim(string_cat(file_lines,' ')) < 1) return
+    if (len_trim(file_lines) < 1) return
 
     f_source%digest = fnv_1a(file_lines)
 
@@ -392,7 +392,7 @@ function parse_c_source(c_filename,error) result(c_source)
     close(fh)
 
     ! Ignore empty files, returned as FPM_UNIT_UNKNOW
-    if (len_trim(string_cat(file_lines,' ')) < 1) then
+    if (len_trim(file_lines) < 1) then
         c_source%unit_type = FPM_UNIT_UNKNOWN
         return
     end if
diff --git a/fpm/src/fpm_strings.f90 b/fpm/src/fpm_strings.f90
index 5b6104c..e3cee28 100644
--- a/fpm/src/fpm_strings.f90
+++ b/fpm/src/fpm_strings.f90
@@ -4,13 +4,17 @@ implicit none
 
 private
 public :: f_string, lower, split, str_ends_with, string_t
-public :: string_array_contains, string_cat, operator(.in.), fnv_1a
+public :: string_array_contains, string_cat, len_trim, operator(.in.), fnv_1a
 public :: resize, str
 
 type string_t
     character(len=:), allocatable :: s
 end type
 
+interface len_trim
+    module procedure :: string_len_trim
+end interface len_trim
+
 interface resize
   module procedure :: resize_string
 end interface
@@ -200,6 +204,19 @@ function string_cat(strings,delim) result(cat)
 
 end function string_cat
 
+
+!> Determine total trimmed length of `string_t` array
+pure function string_len_trim(strings) result(n)
+    type(string_t), intent(in) :: strings(:)
+    integer :: i, n
+
+    n = 0
+    do i=1,size(strings)
+        n = n + len_trim(strings(i)%s)
+    end do
+
+end function string_len_trim
+
 subroutine split(input_line,array,delimiters,order,nulls)
     ! parse string on delimiter characters and store tokens into an allocatable array"
     ! Author: John S. Urban
-- 
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