Adding ability to parse float from number with leading decimal (#831)

* Adding ability to parse float from number with leading decimal

* Fixing deprecated std::usize::MAX constant per https://doc.rust-lang.org/core/usize/constant.MAX.html and making consistent with other usages

* Add test case for 2. and issue link

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

arrow/src/csv/reader.rs

@@ -60,7 +60,7 @@ use crate::record_batch::RecordBatch;
 use csv_crate::{ByteRecord, StringRecord};
 
 lazy_static! {
-    static ref DECIMAL_RE: Regex = Regex::new(r"^-?(\d+\.\d+)$").unwrap();
+    static ref DECIMAL_RE: Regex = Regex::new(r"^-?(\d*\.\d+)$").unwrap();
     static ref INTEGER_RE: Regex = Regex::new(r"^-?(\d+)$").unwrap();
     static ref BOOLEAN_RE: Regex = RegexBuilder::new(r"^(true)$|^(false)$")
         .case_insensitive(true)
@@ -271,7 +271,7 @@ pub fn infer_schema_from_files(
     has_header: bool,
 ) -> Result<Schema> {
     let mut schemas = vec![];
-    let mut records_to_read = max_read_records.unwrap_or(std::usize::MAX);
+    let mut records_to_read = max_read_records.unwrap_or(usize::MAX);
 
     for fname in files.iter() {
         let (schema, records_read) = infer_file_schema(
@@ -1342,6 +1342,9 @@ mod tests {
         assert_eq!(infer_field_schema("\"123\""), DataType::Utf8);
         assert_eq!(infer_field_schema("10"), DataType::Int64);
         assert_eq!(infer_field_schema("10.2"), DataType::Float64);
+        assert_eq!(infer_field_schema(".2"), DataType::Float64);
+        // Should be parsed as Float or Int. See https://github.com/apache/arrow-rs/issues/929
+        assert_eq!(infer_field_schema("2."), DataType::Utf8);
         assert_eq!(infer_field_schema("true"), DataType::Boolean);
         assert_eq!(infer_field_schema("false"), DataType::Boolean);
         assert_eq!(infer_field_schema("2020-11-08"), DataType::Date32);