From cd5b025ef85075f502fd52813dcc56ce9c8ce3cf Mon Sep 17 00:00:00 2001
From: =?utf8?q?=C5=81ukasz=20Wojni=C5=82owicz?=
 <lukasz.wojnilowicz@gmail.com>
Date: Sat, 2 May 2020 11:39:21 +0200
Subject: [PATCH] ICU-20545 Detect file separator char from dir

If udata_create won't find U_FILE_SEP_CHAR at the end of a dir variable,
then it appends it. The problem starts if the dir variable uses
U_FILE_ALT_SEP_CHAR which is not equal to U_FILE_SEP_CHAR. Then the
resulting path could look like this
../data\mappings/cns-11643-1992.ucm
instead of this
../data/mappings/cns-11643-1992.ucm

This patch uses U_FILE_SEP_CHAR unless it detects that the dir variable
doesn't use it, and uses U_FILE_ALT_SEP_CHAR instead.
---
 icu4c/source/tools/toolutil/unewdata.cpp | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/icu4c/source/tools/toolutil/unewdata.cpp b/icu4c/source/tools/toolutil/unewdata.cpp
index 32b615c39b8..43ff16b6eec 100644
--- a/icu4c/source/tools/toolutil/unewdata.cpp
+++ b/icu4c/source/tools/toolutil/unewdata.cpp
@@ -56,15 +56,25 @@ udata_create(const char *dir, const char *type, const char *name,
         *pErrorCode=U_MEMORY_ALLOCATION_ERROR;
         return NULL;
     }
-    
+
+    char dirSepChar = U_FILE_SEP_CHAR;
+#if (U_FILE_SEP_CHAR != U_FILE_ALT_SEP_CHAR)
+    // We may need to append a different directory separator when building for Cygwin or MSYS2.
+    if(dir && *dir) {
+      if(!uprv_strchr(dir, U_FILE_SEP_CHAR) && uprv_strchr(dir, U_FILE_ALT_SEP_CHAR)) {
+          dirSepChar = U_FILE_ALT_SEP_CHAR;
+      }
+    }
+#endif
+
     /* Check that the full path won't be too long */
     length = 0;					/* Start with nothing */
     if(dir != NULL  && *dir !=0)	/* Add directory length if one was given */
     {
     	length += static_cast<int32_t>(strlen(dir));
-	
+
     	/* Add 1 if dir doesn't end with path sep */
-        if (dir[strlen(dir) - 1]!= U_FILE_SEP_CHAR) {
+        if (dir[strlen(dir) - 1]!= dirSepChar) {
             length++;
         }
 	}
@@ -74,7 +84,7 @@ udata_create(const char *dir, const char *type, const char *name,
         length += static_cast<int32_t>(strlen(type));
     }
 
-        
+
      /* LDH buffer Length error check */
     if(length  > ((int32_t)sizeof(filename) - 1))
     {
@@ -82,13 +92,13 @@ udata_create(const char *dir, const char *type, const char *name,
    	    uprv_free(pData);
 	    return NULL;
     }
-   
+
     /* open the output file */
     if(dir!=NULL && *dir!=0) { /* if dir has a value, we prepend it to the filename */
         char *p=filename+strlen(dir);
         uprv_strcpy(filename, dir);
-        if (*(p-1)!=U_FILE_SEP_CHAR) {
-            *p++=U_FILE_SEP_CHAR;
+        if (*(p-1)!=dirSepChar) {
+            *p++=dirSepChar;
             *p=0;
         }
     } else { /* otherwise, we'll output to the current dir */
-- 
2.40.0