fix: symbolic linking (ln -s) with pre-existing installation (#1135)

* fix: symbolic linking (`ln -s`) failure with pre-existing installation

* fix: symbolic linking (`ln -s`) failure with pre-existing installation, also for osx prepare_installation.sh script

* docs: add news file

* Rename fix-symbolic-linking to 1135-fix-symbolic-linking

* Apply suggestion from @marcoesters

---------

Co-authored-by: Marco Esters <mesters@anaconda.com>

Author: dlaehnemann

constructor/header.sh

@@ -501,7 +501,7 @@ chmod +x "$CONDA_EXEC"
 
 {%- if conda_exe_name != "_conda" %}
 # In case there are packages that depend on _conda
-ln -s "$CONDA_EXEC" "$PREFIX"/_conda
+ln -s -f "$CONDA_EXEC" "$PREFIX"/_conda
 {%- endif %}
 
 {%- for filename, (start, end, executable) in conda_exe_payloads|items %}

constructor/osx/prepare_installation.sh

@@ -32,7 +32,7 @@ chmod +x "$CONDA_EXEC"
 
 {%- if conda_exe_name != "_conda" %}
 # In case there are packages that depend on _conda
-ln -s "$CONDA_EXEC" "$PREFIX"/_conda
+ln -s -f "$CONDA_EXEC" "$PREFIX"/_conda
 {%- endif %}
 
 # Create a blank history file so conda thinks this is an existing env

news/1135-fix-symbolic-linking

@@ -0,0 +1,3 @@
+### Bug fixes
+
+* Force symbolic linking of `_conda` in SH and PKG installers. This fixes a regression introduced by #1090 that made installations fail if `_conda` already exists in the target location. (#1135)