Add option to control trailing zero in floating-point literals (#5834)

Add `float_literal_trailing_zero` option

Configurations.md

@@ -1256,6 +1256,56 @@ Control the case of the letters in hexadecimal literal values
 - **Possible values**: `Preserve`, `Upper`, `Lower`
 - **Stable**: No (tracking issue: [#5081](https://github.com/rust-lang/rustfmt/issues/5081))
 
+## `float_literal_trailing_zero`
+
+Control the presence of trailing zero in floating-point literal values
+
+- **Default value**: `Preserve`
+- **Possible values**: `Preserve`, `Always`, `IfNoPostfix`, `Never`
+- **Stable**: No (tracking issue: [#6471](https://github.com/rust-lang/rustfmt/issues/6471))
+
+#### `Preserve` (default):
+
+Leave the literal as-is.
+
+```rust
+fn main() {
+    let values = [1.0, 2., 3.0e10, 4f32];
+}
+```
+
+#### `Always`:
+
+Add a trailing zero to the literal:
+
+```rust
+fn main() {
+    let values = [1.0, 2.0, 3.0e10, 4.0f32];
+}
+```
+
+#### `IfNoPostfix`:
+
+Add a trailing zero by default. If the literal contains an exponent or a suffix, the zero
+and the preceding period are removed:
+
+```rust
+fn main() {
+    let values = [1.0, 2.0, 3e10, 4f32];
+}
+```
+
+#### `Never`:
+
+Remove the trailing zero. If the literal contains an exponent or a suffix, the preceding
+period is also removed:
+
+```rust
+fn main() {
+    let values = [1., 2., 3e10, 4f32];
+}
+```
+
 ## `hide_parse_errors`
 
 This option is deprecated and has been renamed to `show_parse_errors` to avoid confusion around the double negative default of `hide_parse_errors=false`.

src/chains.rs

@@ -264,7 +264,7 @@ impl ChainItemKind {
                 return (
                     ChainItemKind::Parent {
                         expr: expr.clone(),
-                        parens: is_method_call_receiver && should_add_parens(expr),
+                        parens: is_method_call_receiver && should_add_parens(expr, context),
                     },
                     expr.span,
                 );
@@ -1049,12 +1049,12 @@ fn trim_tries(s: &str) -> String {
 /// 1. .method();
 /// ```
 /// Which all need parenthesis or a space before `.method()`.
-fn should_add_parens(expr: &ast::Expr) -> bool {
+fn should_add_parens(expr: &ast::Expr, context: &RewriteContext<'_>) -> bool {
     match expr.kind {
-        ast::ExprKind::Lit(ref lit) => crate::expr::lit_ends_in_dot(lit),
+        ast::ExprKind::Lit(ref lit) => crate::expr::lit_ends_in_dot(lit, context),
         ast::ExprKind::Closure(ref cl) => match cl.body.kind {
             ast::ExprKind::Range(_, _, ast::RangeLimits::HalfOpen) => true,
-            ast::ExprKind::Lit(ref lit) => crate::expr::lit_ends_in_dot(lit),
+            ast::ExprKind::Lit(ref lit) => crate::expr::lit_ends_in_dot(lit, context),
             _ => false,
         },
         _ => false,

src/config/mod.rs

@@ -79,6 +79,8 @@ create_config! {
     skip_macro_invocations: SkipMacroInvocations, false,
         "Skip formatting the bodies of macros invoked with the following names.";
     hex_literal_case: HexLiteralCaseConfig, false, "Format hexadecimal integer literals";
+    float_literal_trailing_zero: FloatLiteralTrailingZeroConfig, false,
+        "Add or remove trailing zero in floating-point literals";
 
     // Single line expressions and items
     empty_item_single_line: EmptyItemSingleLine, false,
@@ -739,6 +741,7 @@ format_macro_matchers = false
 format_macro_bodies = true
 skip_macro_invocations = []
 hex_literal_case = "Preserve"
+float_literal_trailing_zero = "Preserve"
 empty_item_single_line = true
 struct_lit_single_line = true
 fn_single_line = false
@@ -829,6 +832,7 @@ format_macro_matchers = false
 format_macro_bodies = true
 skip_macro_invocations = []
 hex_literal_case = "Preserve"
+float_literal_trailing_zero = "Preserve"
 empty_item_single_line = true
 struct_lit_single_line = true
 fn_single_line = false

src/config/options.rs

@@ -146,6 +146,21 @@ pub enum HexLiteralCase {
     Lower,
 }
 
+/// How to treat trailing zeros in floating-point literals.
+#[config_type]
+pub enum FloatLiteralTrailingZero {
+    /// Leave the literal as-is.
+    Preserve,
+    /// Add a trailing zero to the literal.
+    Always,
+    /// Add a trailing zero by default. If the literal contains an exponent or a suffix, the zero
+    /// and the preceding period are removed.
+    IfNoPostfix,
+    /// Remove the trailing zero. If the literal contains an exponent or a suffix, the preceding
+    /// period is also removed.
+    Never,
+}
+
 #[config_type]
 pub enum ReportTactic {
     Always,
@@ -613,6 +628,8 @@ config_option_with_style_edition_default!(
     FormatMacroBodies, bool, _ => true;
     SkipMacroInvocations, MacroSelectors, _ => MacroSelectors::default();
     HexLiteralCaseConfig, HexLiteralCase, _ => HexLiteralCase::Preserve;
+    FloatLiteralTrailingZeroConfig, FloatLiteralTrailingZero, _ =>
+        FloatLiteralTrailingZero::Preserve;
 
     // Single line expressions and items
     EmptyItemSingleLine, bool, _ => true;