installer: offer pseudo console support as an experimental option

Cygwin runtime v3.1.x came with a really cool new feature: pseudo
console support. Theoretically, this allows users to run native console
programs in a MinTTY without having to use winpty. Practically, the
feature is unfortunately still too buggy to unleash onto the Git for
Windows user masses. But we can offer it as an experimental option so
that users can provide early feedback.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

installer/install.iss

@@ -368,12 +368,17 @@ const
 #define HAVE_EXPERIMENTAL_OPTIONS 1
 #endif
 
+#ifdef WITH_EXPERIMENTAL_PCON
+#define HAVE_EXPERIMENTAL_OPTIONS 1
+#endif
+
 #ifdef HAVE_EXPERIMENTAL_OPTIONS
     // Experimental options
     GP_BuiltinDifftool = 1;
     GP_BuiltinRebase   = 2;
     GP_BuiltinStash    = 3;
     GP_BuiltinAddI     = 4;
+    GP_EnablePCon      = 5;
 #endif
 
 var
@@ -440,7 +445,7 @@ var
 #ifdef HAVE_EXPERIMENTAL_OPTIONS
     // Wizard page and variables for the experimental options.
     ExperimentalOptionsPage:TWizardPage;
-    RdbExperimentalOptions:array[GP_BuiltinDifftool..GP_BuiltinAddI] of TCheckBox;
+    RdbExperimentalOptions:array[GP_BuiltinDifftool..GP_EnablePCon] of TCheckBox;
 #endif
 
     // Mapping controls to hyperlinks
@@ -2091,6 +2096,14 @@ begin
     RdbExperimentalOptions[GP_BuiltinAddI].Checked:=ReplayChoice('Enable Builtin Interactive Add','Auto')='Enabled';
 #endif
 
+#ifdef WITH_EXPERIMENTAL_PCON
+    // 5th option
+    RdbExperimentalOptions[GP_EnablePCon]:=CreateCheckBox(ExperimentalOptionsPage,'Enable experimental support for pseudo consoles.','<RED>(NEW!)</RED> This allows running native console programs like Node or Python in a'+#13+'Git Bash window without using winpty, but it still has known bugs.',TabOrder,Top,Left);
+
+    // Restore the settings chosen during a previous install
+    RdbExperimentalOptions[GP_EnablePCon].Checked:=ReplayChoice('Enable Pseudo Console Support','Auto')='Disabled';
+#endif
+
 #endif
 
     PageIDBeforeInstall:=CurrentCustomPageID;
@@ -2769,6 +2782,12 @@ begin
         GitSystemConfigSet('add.interactive.useBuiltin',#0);
 #endif
 
+#ifdef WITH_EXPERIMENTAL_PCON
+    if RdbExperimentalOptions[GP_EnablePCon].checked and
+       not SaveStringToFile(ExpandConstant('{app}\etc\git-bash.config'),'MSYS=enable_pcon',False) then
+        LogError('Could not write to '+ExpandConstant('{app}\etc\git-bash.config'));
+#endif
+
     {
         Modify the environment
 
@@ -3112,6 +3131,14 @@ begin
     RecordChoice(PreviousDataKey,'Enable Builtin Interactive Add',Data);
 #endif
 
+#ifdef WITH_EXPERIMENTAL_PCON
+    Data:='Disabled';
+    if RdbExperimentalOptions[GP_EnablePCon].Checked then begin
+        Data:='Enabled';
+    end;
+    RecordChoice(PreviousDataKey,'Enable Pseudo Console Support',Data);
+#endif
+
     Path:=ExpandConstant('{app}\etc\install-options.txt');
     if not SaveStringToFile(Path,ChosenOptions,False) then
         LogError('Could not write to '+Path);

installer/release.sh

@@ -181,6 +181,11 @@ then
 	inno_defines="$inno_defines$LF#define WITH_EXPERIMENTAL_BUILTIN_ADD_I 1"
 fi
 
+if grep -q enable_pcon /usr/bin/msys-2.0.dll
+then
+	inno_defines="$inno_defines$LF#define WITH_EXPERIMENTAL_PCON 1"
+fi
+
 GITCONFIG_PATH="$(echo "$LIST" | grep "^$etc_gitconfig\$")"
 test -z "$GITCONFIG_PATH" || {
 	keys="$(git config -f "/$GITCONFIG_PATH" -l --name-only)" &&