From 5c19b44f351ab0f6fc2fd2823e2d5096fb3be671 Mon Sep 17 00:00:00 2001
From: Charlie Marsh <charlie.r.marsh@gmail.com>
Date: Fri, 13 Oct 2023 17:13:42 -0400
Subject: [PATCH] Add trailing zero between dot and exponential

---
 .../test/fixtures/ruff/expression/number.py   |  7 +++++
 .../src/expression/number.rs                  | 11 ++++---
 .../format@expression__number.py.snap         | 30 +++++++++++++++++++
 3 files changed, 44 insertions(+), 4 deletions(-)
 create mode 100644 crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/number.py
 create mode 100644 crates/ruff_python_formatter/tests/snapshots/format@expression__number.py.snap

diff --git a/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/number.py b/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/number.py
new file mode 100644
index 00000000000000..afed916b61aa53
--- /dev/null
+++ b/crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/number.py
@@ -0,0 +1,7 @@
+.1
+1.
+1E+1
+1E-1
+1.E+1
+1.0E+1
+1.1E+1
diff --git a/crates/ruff_python_formatter/src/expression/number.rs b/crates/ruff_python_formatter/src/expression/number.rs
index 130640f48ff1a1..b26ba950614c4e 100644
--- a/crates/ruff_python_formatter/src/expression/number.rs
+++ b/crates/ruff_python_formatter/src/expression/number.rs
@@ -142,7 +142,7 @@ fn normalize_floating_number(input: &str) -> Cow<str> {
 
     let mut chars = input.char_indices();
 
-    let fraction_ends_with_dot = if let Some((index, '.')) = chars.next() {
+    let mut prev_char_is_dot = if let Some((index, '.')) = chars.next() {
         // Add a leading `0` if `input` starts with `.`.
         output.push('0');
         output.push('.');
@@ -155,8 +155,8 @@ fn normalize_floating_number(input: &str) -> Cow<str> {
     loop {
         match chars.next() {
             Some((index, c @ ('e' | 'E'))) => {
-                if fraction_ends_with_dot {
-                    // Add `0` if fraction part ends with `.`.
+                if prev_char_is_dot {
+                    // Add `0` if the `e` immediately follows a `.` (e.g., `1.e1`).
                     output.push_str(&input[last_index..index]);
                     output.push('0');
                     last_index = index;
@@ -177,7 +177,10 @@ fn normalize_floating_number(input: &str) -> Cow<str> {
 
                 break;
             }
-            Some(_) => continue,
+            Some((_index, c)) => {
+                prev_char_is_dot = c == '.';
+                continue;
+            }
             None => {
                 if input.ends_with('.') {
                     // Add `0` if fraction part ends with `.`.
diff --git a/crates/ruff_python_formatter/tests/snapshots/format@expression__number.py.snap b/crates/ruff_python_formatter/tests/snapshots/format@expression__number.py.snap
new file mode 100644
index 00000000000000..c237b3c297ec17
--- /dev/null
+++ b/crates/ruff_python_formatter/tests/snapshots/format@expression__number.py.snap
@@ -0,0 +1,30 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/number.py
+---
+## Input
+```py
+.1
+1.
+1E+1
+1E-1
+1.E+1
+1.0E+1
+1.1E+1
+-1.e49
+```
+
+## Output
+```py
+0.1
+1.0
+1e1
+1e-1
+1.0e1
+1.0e1
+1.1e1
+-1.0e49
+```
+
+
+