Document overflow behavior, add tests. (google#130)

Overflow for int, uint, timestamp, and duration.

doc/langdef.md

@@ -827,6 +827,12 @@ values. The ordering operators obey the usual algebraic properties, i.e. `e1 <=
 e2` gives the same result as `!(e1 > e2)` as well as `(e1 < e2) || (e1 == e2)`
 when the expressions involved do not have side effects.
 
+### Overflow
+
+Arithmetic operations raise an error when the results exceed the range of the
+integer type (int, uint) or the timestamp or duration type.  An error is also
+raised for conversions which exceed the range of the target type.
+
 ### Timezones
 
 Timezones are expressed in the following grammar:

tests/simple/testdata/integer_math.textproto

@@ -190,8 +190,6 @@ section {
     eval_error: {
       errors: { message: "return error for overflow" }
     }
-    ## Current behavior:
-    ## value: { int64_value: -9223372036854775808 }
   }
   test {
     name: "int64_overflow_negative"
@@ -200,8 +198,14 @@ section {
     eval_error: {
       errors: { message: "return error for overflow" }
     }
-    ## Current behavior:
-    ## value: { int64_value: 9223372036854775807 }
+  }
+  test {
+    name: "int64_min_negate"
+    description: "Negated LLONG_MIN is not representable."
+    expr: "-(-9223372036854775808)"
+    eval_error: {
+      errors: { message: "return error for overflow" }
+    }
   }
   test {
     name: "uint64_overflow_positive"

tests/simple/testdata/timestamps.textproto

@@ -343,3 +343,67 @@ section {
     value: { int64_value: 3730 }
   }
 }
+section {
+  name: "timestamp_range"
+  description: "Tests for out-of-range operations on timestamps."
+  test {
+    name: "from_string_under"
+    expr: "timestamp('0000-01-01T00:00:00Z')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "from_string_over"
+    expr: "timestamp('10000-01-01T00:00:00Z')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "add_duration_under"
+    expr: "timestamp('0001-01-01T00:00:00Z') - duration('10s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "add_duration_over"
+    expr: "timestamp('9999-12-31T23:59:59Z') + duration('10s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+}
+section {
+  name: "duration_range"
+  description: "Tests for out-of-range operations on durations."
+  test {
+    name: "from_string_under"
+    expr: "duration('-320000000000s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "from_string_over"
+    expr: "duration('320000000000s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "add_under"
+    expr: "duration('-200000000000s') + duration('-200000000000s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+  test {
+    name: "add_over"
+    expr: "duration('200000000000s') + duration('200000000000s')"
+    eval_error {
+      errors { message: "range" }
+    }
+  }
+}