[arrow] branch master updated: ARROW-2471: [Rust] Builder zero capacity fix

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The following commit(s) were added to refs/heads/master by this push:
     new 46fe09a  ARROW-2471: [Rust] Builder zero capacity fix
46fe09a is described below

commit 46fe09a6c9a4d7cd79f4afdae1f527fdd74e6bfb
Author: Andy Grove <an...@gmail.com>
AuthorDate: Fri Apr 20 10:16:26 2018 +0200

    ARROW-2471: [Rust] Builder zero capacity fix
    
    Author: Andy Grove <an...@gmail.com>
    
    Closes #1911 from andygrove/builder_zero_capacity_fix and squashes the following commits:
    
    8292bc7 <Andy Grove> fix merge conflict
    589ef71 <Andy Grove> Merge remote-tracking branch 'upstream/master'
    cfa7574 <Andy Grove> bug fix: it is now valid to create a builder with zero capacity and then push values to it
    bd4fbb5 <Andy Grove> Merge remote-tracking branch 'upstream/master'
    9c8a10a <Andy Grove> Merge remote-tracking branch 'upstream/master'
    05592f8 <Andy Grove> Merge remote-tracking branch 'upstream/master'
    8c0e698 <Andy Grove> Merge remote-tracking branch 'upstream/master'
    31ef90b <Andy Grove> Merge remote-tracking branch 'upstream/master'
    2f87c70 <Andy Grove> Fix build - add missing import
---
 rust/src/array.rs        |  7 +++++++
 rust/src/builder.rs      | 13 +++++++++++--
 rust/src/list_builder.rs | 13 ++++++++++++-
 rust/src/memory_pool.rs  |  2 +-
 4 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/rust/src/array.rs b/rust/src/array.rs
index 63d1130..55881f5 100644
--- a/rust/src/array.rs
+++ b/rust/src/array.rs
@@ -277,6 +277,13 @@ mod tests {
     }
 
     #[test]
+    fn test_from_empty_vec() {
+        let v: Vec<i32> = vec![];
+        let a = Array::from(v);
+        assert_eq!(0, a.len());
+    }
+
+    #[test]
     fn test_from_optional_i32() {
         let a = Array::from(vec![Some(1), None, Some(2), Some(3), None]);
         assert_eq!(5, a.len());
diff --git a/rust/src/builder.rs b/rust/src/builder.rs
index 89e0004..69884cc 100644
--- a/rust/src/builder.rs
+++ b/rust/src/builder.rs
@@ -83,8 +83,9 @@ impl<T> Builder<T> {
     pub fn push(&mut self, v: T) {
         assert!(!self.data.is_null());
         if self.len == self.capacity {
-            let new_capacity = self.capacity;
-            self.grow(new_capacity * 2);
+            // grow capacity by 64 bytes or double the current capacity, whichever is greater
+            let new_capacity = cmp::max(64, self.capacity * 2);
+            self.grow(new_capacity);
         }
         assert!(self.len < self.capacity);
         unsafe {
@@ -175,6 +176,14 @@ mod tests {
     }
 
     #[test]
+    fn test_builder_i32_alloc_zero_bytes() {
+        let mut b: Builder<i32> = Builder::with_capacity(0);
+        b.push(123);
+        let a = b.finish();
+        assert_eq!(1, a.len());
+    }
+
+    #[test]
     fn test_builder_i32() {
         let mut b: Builder<i32> = Builder::with_capacity(5);
         for i in 0..5 {
diff --git a/rust/src/list_builder.rs b/rust/src/list_builder.rs
index 96dca18..71547d2 100644
--- a/rust/src/list_builder.rs
+++ b/rust/src/list_builder.rs
@@ -55,7 +55,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn test_list_u8() {
+    fn test_list_u8_default_capacity() {
         let mut b: ListBuilder<u8> = ListBuilder::new();
         b.push("Hello, ".as_bytes());
         b.push("World!".as_bytes());
@@ -67,6 +67,17 @@ mod tests {
     }
 
     #[test]
+    fn test_list_u8_zero_capacity() {
+        let mut b: ListBuilder<u8> = ListBuilder::with_capacity(0);
+        b.push("Hello, ".as_bytes());
+        b.push("World!".as_bytes());
+        let buffer = b.finish();
+        assert_eq!(2, buffer.len());
+        assert_eq!("Hello, ".as_bytes(), buffer.slice(0));
+        assert_eq!("World!".as_bytes(), buffer.slice(1));
+    }
+
+    #[test]
     fn test_empty_lists() {
         let mut b: ListBuilder<u8> = ListBuilder::new();
         b.push("Hello, ".as_bytes());
diff --git a/rust/src/memory_pool.rs b/rust/src/memory_pool.rs
index acfcc30..6832cd2 100644
--- a/rust/src/memory_pool.rs
+++ b/rust/src/memory_pool.rs
@@ -16,8 +16,8 @@
 // under the License.
 
 use libc;
-use std::mem;
 use std::cmp;
+use std::mem;
 
 use super::error::ArrowError;
 use super::error::Result;

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