fix for #11536 and other terminal and shell environment issues

[philwalk]

fix for #11536

Also verified working REPL for various combinations of Terminal and Windows shell.
See https://github.com/lampepfl/dotty/issues/11536#issuecomment-786156696

[philwalk]

NOTE: hopefully this comment isn't confusing, it's an idea for a proposed change, but is not part of this PR.

Currently, calling scripts results in bin/common being sourced twice, first by bin/scala, then by bin/scalac.
We can cut some significant time from script startups, by the following changes:

1. export variables at the bottom of dist/bin/common
2. conditionally source bin/common, only if variables are not already initialized

Here's what the change looks like in bin/scalac:

# only need to source common if variables not already initialized
[[ -z "$PSEP" && -z "$DOTTY_COMP" ]] && source "$PROG_HOME/bin/common"

In my environment, it eliminates between 250 and 350 milliseconds from script startups, when a compile is required.

[michelou]

@philwalk Usage of eval and onExit is not consistent across the three bash scripts :

$ git diff dist\bin\scalac dist\bin\scaladoc
diff --git a/dist/bin/scalac b/dist/bin/scalac
index f81c20853b..74bfc4a603 100755
--- a/dist/bin/scalac
+++ b/dist/bin/scalac
@@ -120,7 +120,7 @@ if [ "$PROG_NAME" == "$ScriptingMain" ]; then
   scripting_string="-script $target_script ${scripting_args[@]}"
 fi

-eval exec "\"$JAVACMD\"" \
+eval "\"$JAVACMD\"" \
      ${JAVA_OPTS:-$default_java_opts} \
      "${DEBUG-}" \
      "${java_args[@]}" \
@@ -130,4 +130,5 @@ eval exec "\"$JAVACMD\"" \
      "${scala_args[@]}" \
      "${residual_args[@]}" \
      "${scripting_string-}"
-exit $?
+scala_exit_status=$?
+onExit
diff --git a/dist/bin/scaladoc b/dist/bin/scaladoc
index b536dbf99e..304da8f504 100755
--- a/dist/bin/scaladoc
+++ b/dist/bin/scaladoc
@@ -125,7 +125,7 @@ done

 classpathArgs

-eval exec "\"$JAVACMD\"" \
+eval "\"$JAVACMD\"" \
      ${JAVA_OPTS:-$default_java_opts} \
      "$DEBUG" \
      "${java_args[@]}" \
@@ -134,4 +134,5 @@ eval exec "\"$JAVACMD\"" \
      "${scala_args[@]}" \
      "${residual_args[@]}" \
      "$scripting_string"
-exit $?
+scala_exit_status=$?
+onExit

Do we agree with the following general rules ?!

• do not write eval exec <something>.
• a call to eval is always followed by the assignment scala_exit_status=$?.
• onExit is always the last executed instructon in the script.

[philwalk]

@michelou
The rules sound correct to me, I will make the suggested change to dist\bin\scaladoc and do some manual testing.

[philwalk]

@michelou - I'm not able to exhaustively test the change to dist/bin/scaladoc, although it's is pretty simple. Should I push the updated version?

[michelou]

@michelou - I'm not able to exhaustively test the change to dist/bin/scaladoc, although it's is pretty simple. Should I push the updated version?

I'd like to keep scalac and scaladoc in sync. So yes.