fix(convert): return error when conversion exceeds f64 bounds

Prior to this commit, string values that would exceed the f64 bounds would
return `f64::INFINITY`. This leaks a type into the VRL scripts that could
cause a panic without support to check for the value.

Fixes vectordotdev#1107

changelog.d/1107.breaking.md

@@ -0,0 +1,2 @@
+Fixes the `to_float` function to return an error instead of "infinity" when parsing a string outside
+the f64::MAX / f64::MIN bounds.

src/compiler/conversion/mod.rs

@@ -159,6 +159,11 @@ impl Conversion {
                 let parsed = s
                     .parse::<f64>()
                     .with_context(|_| FloatParseSnafu { s: s.clone() })?;
+                if !parsed.is_normal() {
+                    return Err(Error::NanFloat {
+                        s: format!("Invalid float \"{s}\": number too large to fit in target type"),
+                    });
+                }
                 let f = NotNan::new(parsed).map_err(|_| Error::NanFloat { s: s.to_string() })?;
                 f.into()
             }

src/compiler/conversion/tests/mod.rs

@@ -2,7 +2,8 @@ use bytes::Bytes;
 use chrono::{DateTime, Utc};
 use ordered_float::NotNan;
 
-use crate::compiler::conversion::parse_bool;
+use crate::compiler::conversion::{parse_bool, Conversion, Error};
+use crate::compiler::TimeZone;
 
 #[cfg(unix)] // see https://github.com/vectordotdev/vector/issues/1201
 mod unix;
@@ -91,3 +92,34 @@ fn parse_bool_errors() {
     assert!(parse_bool("yes or no").is_err());
     assert!(parse_bool("123.4").is_err());
 }
+
+fn convert_float(input: impl ToString) -> Result<StubValue, Error> {
+    let input = input.to_string();
+    let converter = Conversion::parse("float", TimeZone::Local).expect("float conversion");
+    converter.convert::<StubValue>(input.into())
+}
+
+#[test]
+fn convert_float_ok() {
+    let max_float = format!("17976931348623157{}", "0".repeat(292));
+    let min_float = format!("-{max_float}");
+
+    assert_eq!(convert_float(max_float), Ok(StubValue::Float(f64::MAX)));
+    assert_eq!(convert_float("1"), Ok(StubValue::Float(1.0)));
+    assert_eq!(convert_float("1.23"), Ok(StubValue::Float(1.23)));
+    assert_eq!(convert_float("-1"), Ok(StubValue::Float(-1.0)));
+    assert_eq!(convert_float("-1.23"), Ok(StubValue::Float(-1.23)));
+    assert_eq!(convert_float(min_float), Ok(StubValue::Float(f64::MIN)));
+}
+
+#[test]
+fn convert_float_errors() {
+    let exceeds_max_float = format!("17976931348623159{}", "0".repeat(292)); // last number inc by 2
+    let exceeds_min_float = format!("-{exceeds_max_float}");
+
+    assert!(convert_float("abc").is_err());
+    assert!(convert_float("1.23.4").is_err());
+    assert!(convert_float(exceeds_max_float).is_err());
+    assert!(convert_float(exceeds_min_float).is_err());
+    assert!(convert_float("0.0").is_err());
+}