Fix bug with ${var%''}.

The issue is that we were computing s[:-0] when the suffix is empty.
Added an explicit check to fix it.

Addresses issue #291.

I also moved the spec tests around.  This bug was reported by Crestwave
as the "nested strip" case in spec/var-op-strip.

osh/string_ops.py

@@ -174,13 +174,13 @@ def DoUnarySuffixOp(s, op, arg):
     arg = glob_.GlobUnescape(arg)
 
     if op.op_id in (Id.VOp1_Pound, Id.VOp1_DPound):  # const prefix
-      if s.startswith(arg):
+      if arg and s.startswith(arg):  # explicit check for non-empty arg
         return s[len(arg):]
       else:
         return s
 
     elif op.op_id in (Id.VOp1_Percent, Id.VOp1_DPercent):  # const suffix
-      if s.endswith(arg):
+      if arg and s.endswith(arg):  # need explicit check for non-empty arg
         return s[:-len(arg)]
       else:
         return s

osh/word_eval.py

@@ -420,7 +420,7 @@ def _ApplyUnarySuffixOp(self, val, op):
 
       if val.tag == value_e.Str:
         s = string_ops.DoUnarySuffixOp(val.s, op, arg_val.s)
-        #log('%s %s -> %s', val.s, arg_val.s, s)
+        #log('%r %r -> %r', val.s, arg_val.s, s)
         new_val = value.Str(s)
       else:  # val.tag == value_e.StrArray:
         # ${a[@]#prefix} is VECTORIZED on arrays.  Oil should have this too.

spec/bugs.test.sh

@@ -20,89 +20,3 @@ echo $a
 ## N-I dash/ash stdout-json: ""
 ## N-I dash/ash status: 2
 
-#### Nested % and # operators (looks like a bug, reported by Crestwave)
-var=$'\n'
-argv.py "${var#?}"
-argv.py "${var%''}"
-argv.py "${var%"${var#?}"}"
-var='a'
-argv.py "${var#?}"
-argv.py "${var%''}"
-argv.py "${var%"${var#?}"}"
-## STDOUT:
-['']
-['\n']
-['\n']
-['']
-['a']
-['a']
-## END
-## N-I dash STDOUT:
-['\\n']
-['$\\n']
-['$']
-['']
-['a']
-['a']
-## END
-
-#### # operator with single quoted arg (dash/ash and bash/mksh disagree, reported by Crestwave)
-var=a
-echo -${var#'a'}-
-echo -"${var#'a'}"-
-var="'a'"
-echo -${var#'a'}-
-echo -"${var#'a'}"-
-## STDOUT:
---
---
--'a'-
--'a'-
-## END
-## OK dash/ash STDOUT:
---
--a-
--'a'-
---
-## END
-
-#### / operator with single quoted arg (causes syntax error in regex in OSH, reported by Crestwave)
-var="++--''++--''"
-echo no plus or minus "${var//[+-]}"
-echo no plus or minus "${var//['+-']}"
-## STDOUT:
-no plus or minus ''''
-no plus or minus ''''
-## END
-## status: 0
-## OK osh STDOUT:
-no plus or minus ''''
-## END
-## OK osh status: 1
-## BUG ash STDOUT:
-no plus or minus ''''
-no plus or minus ++--++--
-## END
-## BUG ash status: 0
-## N-I dash stdout-json: ""
-## N-I dash status: 2
-
-#### single quotes work inside character classes
-x='a[[[---]]]b'
-echo "${x//['[]']}"
-## STDOUT:
-a---b
-## END
-## BUG ash STDOUT:
-a[[[---]]]b
-## END
-## N-I dash stdout-json: ""
-## N-I dash status: 2
-
-#### comparison: :- operator with single quoted arg
-echo ${unset:-'a'}
-echo "${unset:-'a'}"
-## STDOUT:
-a
-'a'
-## END

spec/var-op-strip.test.sh

@@ -175,3 +175,29 @@ foo[]
 [a]foo[]
 foo[]
 ## END
+
+#### Nested % and # operators (bug reported by Crestwave)
+var=$'\n'
+argv.py "${var#?}"
+argv.py "${var%''}"
+argv.py "${var%"${var#?}"}"
+var='a'
+argv.py "${var#?}"
+argv.py "${var%''}"
+argv.py "${var%"${var#?}"}"
+## STDOUT:
+['']
+['\n']
+['\n']
+['']
+['a']
+['a']
+## END
+## N-I dash STDOUT:
+['\\n']
+['$\\n']
+['$']
+['']
+['a']
+['a']
+## END

spec/var-sub-quote.test.sh

@@ -204,3 +204,64 @@ a
 abc
 abc
 ## END
+
+#### # operator with single quoted arg (dash/ash and bash/mksh disagree, reported by Crestwave)
+var=a
+echo -${var#'a'}-
+echo -"${var#'a'}"-
+var="'a'"
+echo -${var#'a'}-
+echo -"${var#'a'}"-
+## STDOUT:
+--
+--
+-'a'-
+-'a'-
+## END
+## OK dash/ash STDOUT:
+--
+-a-
+-'a'-
+--
+## END
+
+#### / operator with single quoted arg (causes syntax error in regex in OSH, reported by Crestwave)
+var="++--''++--''"
+echo no plus or minus "${var//[+-]}"
+echo no plus or minus "${var//['+-']}"
+## STDOUT:
+no plus or minus ''''
+no plus or minus ''''
+## END
+## status: 0
+## OK osh STDOUT:
+no plus or minus ''''
+## END
+## OK osh status: 1
+## BUG ash STDOUT:
+no plus or minus ''''
+no plus or minus ++--++--
+## END
+## BUG ash status: 0
+## N-I dash stdout-json: ""
+## N-I dash status: 2
+
+#### single quotes work inside character classes
+x='a[[[---]]]b'
+echo "${x//['[]']}"
+## STDOUT:
+a---b
+## END
+## BUG ash STDOUT:
+a[[[---]]]b
+## END
+## N-I dash stdout-json: ""
+## N-I dash status: 2
+
+#### comparison: :- operator with single quoted arg
+echo ${unset:-'a'}
+echo "${unset:-'a'}"
+## STDOUT:
+a
+'a'
+## END

test/spec.sh

@@ -229,8 +229,7 @@ osh-only() {
 
 # Regress bugs
 bugs() {
-  sh-spec spec/bugs.test.sh ${REF_SHELLS[@]} $ZSH $BUSYBOX_ASH $OSH_LIST "$@" \
-    --osh-failures-allowed 3
+  sh-spec spec/bugs.test.sh ${REF_SHELLS[@]} $ZSH $BUSYBOX_ASH $OSH_LIST "$@"
 }
 
 blog1() {
@@ -491,7 +490,7 @@ var-num() {
 }
 
 var-sub-quote() {
-  sh-spec spec/var-sub-quote.test.sh \
+  sh-spec spec/var-sub-quote.test.sh --osh-failures-allowed 2 \
     ${REF_SHELLS[@]} $OSH_LIST "$@"
 }