[builtin/test] Implement test --true; test --false

The other part of issue #2094.  Based on feedback from Will Clardy.

Also add a FAQ entry on this, since Julian also ran into it.

builtin/bracket_osh.py

@@ -127,6 +127,10 @@ def _TwoArgs(w_parser):
             unary_id = Id.BoolUnary_f
         elif s0 == '--symlink':
             unary_id = Id.BoolUnary_L
+        elif s0 == '--true':
+            unary_id = Id.BoolUnary_true
+        elif s0 == '--false':
+            unary_id = Id.BoolUnary_false
 
     if unary_id == Id.Undefined_Tok:
         unary_id = match.BracketUnary(w0.s)

doc/ref/chap-builtin-cmd.md

@@ -513,6 +513,30 @@ See the [YSH FAQ][echo-en] for details.
 [simple_echo]: chap-option.html#ysh:all
 [echo-en]: ../ysh-faq.html#how-do-i-write-the-equivalent-of-echo-e-or-echo-n
 
+### ysh-test
+
+The YSH [test](#test) builtin supports these long flags:
+
+    --dir            same as -d
+    --exists         same as -e
+    --file           same as -f
+    --symlink        same as -L
+
+    --true           Is the argument equal to the string "true"?
+    --false          Is the argument equal to the string "false"?
+
+The `--true` and `--false` flags can be used to combine commands and
+expressions:
+
+    if test --file a && test --true $[bool(mydict)] {
+      echo ok
+    }
+
+This works because the boolean `true` *stringifies* to `"true"`, and likewise
+with `false`.
+
+That is, `$[true] === "true"` and `$[false] === "false"`.
+
 ### write
 
 write fixes problems with shell's `echo` builtin.
@@ -1108,8 +1132,8 @@ JOB:
 
 Evaluates a conditional expression and returns 0 (true) or 1 (false).
 
-Note that [ is the name of a builtin, not an operator in the language.  Use
-'test' to avoid this confusion.
+Note that `[` is the name of a builtin, not an operator in the language.  Use
+`test` to avoid this confusion.
 
 String expressions:
 
@@ -1168,12 +1192,9 @@ these are discouraged.
 
 <!--    -R VAR     True if the variable VAR has been set and is a nameref variable. -->
 
-Oils supports these long flags:
+---
 
-    --dir            same as -d
-    --exists         same as -e
-    --file           same as -f
-    --symlink        same as -L
+See [ysh-test](#ysh-test) for log flags like `--file` and `--true`.
 
 ### getopts
 

doc/ref/toc-ysh.md

@@ -126,6 +126,7 @@ X [Wok]           _field()
                   use                    create a module Obj from a source file
   [I/O]           ysh-read               flags --all, -0
                   ysh-echo               no -e -n with simple_echo
+                  ysh-test               --file --true etc.
                   write                  Like echo, with --, --sep, --end
                   fork         forkwait  Replace & and (), and takes a block
                   fopen                  Open multiple streams, takes a block

doc/ysh-faq.md

@@ -205,11 +205,22 @@ not `${}`.
 
 -->
 
-## How do I combine conditional commands and expressions: `if (myvar)` versus `if test`?
+## How do I combine conditional commands and expressions: `if (myvar)` and `if test -f`?
 
-TODO: `test --true --false`
+You can use the `--true` and `--false` flags to the [YSH test][ysh-test]
+builtin:
+
+    if test --true $[myvar] && test --file x {
+        echo ok
+    }
+
+They test if their argument is literally the string `"true"` or `"false"`.
+
+This works because the boolean `true` *stringifies* to `"true"`, and likewise
+with `false`.
+
+[ysh-test]: ref/chap-builtin-cmd.html#ysh-test
 
-This happens in `while` too.
 
 ## Why do I lose the value of `p` in `myproc (&p) | grep foo`?
 

frontend/id_kind_def.py

@@ -109,10 +109,10 @@ def AddBoolKind(
     ):
         # type: (...) -> None
         """
-    Args:
-      kind_name: string
-      arg_type_pairs: dictionary of bool_arg_type_e -> []
-    """
+        Args:
+          kind_name: string
+          arg_type_pairs: dictionary of bool_arg_type_e -> []
+        """
         lexer_pairs = []
         num_tokens = 0
         for arg_type, pairs in arg_type_pairs:
@@ -733,6 +733,15 @@ def AddBoolKinds(spec):
         (bool_arg_type_e.Path, _Dash(list(_UNARY_PATH_CHARS))),
     ])
 
+    Id = spec.id_str2int
+
+    # test --true and test --false have no single letter flags.  They need no
+    # lexing.
+    for long_flag in ('true', 'false'):
+        id_name = 'BoolUnary_%s' % long_flag
+        spec._AddId(id_name)
+        spec.AddBoolOp(Id[id_name], bool_arg_type_e.Str)
+
     spec.AddBoolKind('BoolBinary', [
         (bool_arg_type_e.Str, [
             ('GlobEqual', '='),
@@ -744,7 +753,6 @@ def AddBoolKinds(spec):
         (bool_arg_type_e.Int, _Dash(_BINARY_INT)),
     ])
 
-    Id = spec.id_str2int
     # logical, arity, arg_type
     spec.AddBoolOp(Id['Op_DAmp'], bool_arg_type_e.Undefined)
     spec.AddBoolOp(Id['Op_DPipe'], bool_arg_type_e.Undefined)

osh/sh_expr_eval.py

@@ -1112,6 +1112,10 @@ def EvalB(self, node):
                         return not bool(s)
                     if op_id == Id.BoolUnary_n:
                         return bool(s)
+                    if op_id == Id.BoolUnary_true:
+                        return s == 'true'
+                    if op_id == Id.BoolUnary_false:
+                        return s == 'false'
 
                     raise AssertionError(op_id)  # should never happen
 

spec/ysh-builtins.test.sh

@@ -435,6 +435,92 @@ status=1
 status=2
 ## END
 
+#### test --true; test --false
+shopt --set ysh:upgrade
+
+for expr in (true, false, '', 'other') {
+  pp test_ (expr)
+
+  try {
+    test --true $[expr]
+  }
+  echo true=$[_error.code]
+
+  try {
+    test --false $[expr]
+  }
+  echo false=$[_error.code]
+  echo
+}
+
+## STDOUT:
+(Bool)   true
+true=0
+false=1
+
+(Bool)   false
+true=1
+false=0
+
+(Str)   ""
+true=1
+false=1
+
+(Str)   "other"
+true=1
+false=1
+
+## END
+
+#### More test --true --false
+shopt --set ysh:upgrade
+
+var d = {}
+
+try {
+  test --true $[bool(d)]
+}
+echo dict=$[_error.code]
+
+setvar d.key = 'val'
+
+try {
+  test --true $[bool(d)]
+}
+echo dict=$[_error.code]
+
+echo
+
+if test --true $[bool(d)] && ! test -f / {
+  echo AndOr
+}
+
+## STDOUT:
+dict=1
+dict=0
+
+AndOr
+## END
+
+
+#### Make sure [[ is not affected by --true --false
+
+set +o errexit
+
+$SH +o ysh:all -c '[[ --true ]]; echo dbracket=$?'
+$SH +o ysh:all -c '[[ --false ]]; echo dbracket=$?'
+
+$SH +o ysh:all -c '[[ --true true ]]; echo dbracket=$?'
+echo "parse error $?"
+$SH +o ysh:all -c '[[ --false false ]]; echo dbracket=$?'
+echo "parse error $?"
+
+## STDOUT:
+dbracket=0
+dbracket=0
+parse error 2
+parse error 2
+## END
 
 #### push-registers
 shopt --set ysh:upgrade