Add type conversion function for string -> bool to standard definitions

doc/langdef.md

@@ -708,13 +708,13 @@ macros are:
        function given by the expression `t`, which can use the variable `x`. For
        instance, `[1, 2, 3].map(n, n * n)` evaluates to `[1, 4, 9]`. Any evaluation
        error for any element causes the macro to raise an error.
-  *    transforms a map `e` by taking each key in the map `x` to the function 
+  *    transforms a map `e` by taking each key in the map `x` to the function
        given by the expression `t`, which can use the variable `x`. For
-       instance, `{'one': 1, 'two': 2}.map(k, k)` evaluates to `['one', 'two']`. 
+       instance, `{'one': 1, 'two': 2}.map(k, k)` evaluates to `['one', 'two']`.
        Any evaluation error for any element causes the macro to raise an error.
 *   `e.map(x, p, t)`: Same as the two-arg map but with a conditional `p` filter
     before the value is transformed.
-*   `e.filter(x, p)`: 
+*   `e.filter(x, p)`:
   *    for a list `e`, returns the sublist of all elements `x` which
        evaluate to `true` in the predicate expression `p` (which can use variable
        `x`). For instance, `[1, 2, 3].filter(i, i % 2 > 0)` evaluates to `[1, 3]`.
@@ -1835,7 +1835,7 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="2">
+    <th rowspan="3">
       bool
     </th>
     <td>
@@ -1853,6 +1853,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       identity
     </td>
   </tr>
+  <tr>
+    <td>
+      (string) -> bool
+    </td>
+    <td>
+      type conversion
+    </td>
+  </tr>
   <tr>
     <th rowspan="3">
       bytes

tests/simple/testdata/conversions.textproto

@@ -505,6 +505,74 @@ section {
     value: { uint64_value: 300 }
   }
 }
+section {
+  name: "bool"
+  description: "Conversions to bool"
+  test {
+    name: "string_1"
+    expr: "bool('1')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "string_t"
+    expr: "bool('t')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "string_true_lowercase"
+    expr: "bool('true')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "string_true_uppercase"
+    expr: "bool('TRUE')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "string_true_pascalcase"
+    expr: "bool('True')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "string_0"
+    expr: "bool('0')"
+    value: { bool_value: false }
+  }
+  test {
+    name: "string_f"
+    expr: "bool('f')"
+    value: { bool_value: false }
+  }
+  test {
+    name: "string_false_lowercase"
+    expr: "bool('false')"
+    value: { bool_value: false }
+  }
+  test {
+    name: "string_false_uppercase"
+    expr: "bool('FALSE')"
+    value: { bool_value: false }
+  }
+  test {
+    name: "string_false_pascalcase"
+    expr: "bool('False')"
+    value: { bool_value: false }
+  }
+  test {
+    name: "string_true_badcase"
+    expr: "bool('TrUe')"
+    eval_error {
+      errors { message: "Type conversion error" }
+    }
+  }
+  test {
+    name: "string_false_badcase"
+    expr: "bool('FaLsE')"
+    eval_error {
+      errors { message: "Type conversion error" }
+    }
+  }
+}
 section {
   name: "identity"
   description: "Identity functions"
@@ -535,7 +603,7 @@ section {
   }
   test {
     name: "bytes"
-    expr: "bytes(bytes('abc'))"
+    expr: "bytes(b'abc')"
     value: { bytes_value: "abc" }
   }
   test {

tests/simple/testdata/proto3.textproto

@@ -724,7 +724,7 @@ section {
     eval_error: {
       errors: { message: "unsupported field type" }
     }
-  }  
+  }
   test {
     name: "list_value"
     container: "google.api.expr.test.v1.proto3"