Prevent structs with ".." from being rewritten with alignment

 rustfmt should only support rewriting a struct in an expression
 position with alignment (non-default behavior) when there is no rest
 (with or without a base) and all of the fields are non-shorthand.

Author: ytmimi

src/expr.rs

@@ -1528,12 +1528,12 @@ fn rewrite_struct_lit<'a>(
     let path_shape = shape.sub_width(2)?;
     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
 
-    let has_base = match struct_rest {
+    let has_base_or_rest = match struct_rest {
         ast::StructRest::None if fields.is_empty() => return Some(format!("{} {{}}", path_str)),
         ast::StructRest::Rest(_) if fields.is_empty() => {
             return Some(format!("{} {{ .. }}", path_str));
         }
-        ast::StructRest::Base(_) => true,
+        ast::StructRest::Rest(_) | ast::StructRest::Base(_) => true,
         _ => false,
     };
 
@@ -1542,7 +1542,7 @@ fn rewrite_struct_lit<'a>(
 
     let one_line_width = h_shape.map_or(0, |shape| shape.width);
     let body_lo = context.snippet_provider.span_after(span, "{");
-    let fields_str = if struct_lit_can_be_aligned(fields, has_base)
+    let fields_str = if struct_lit_can_be_aligned(fields, has_base_or_rest)
         && context.config.struct_field_align_threshold() > 0
     {
         rewrite_with_alignment(
@@ -1614,10 +1614,7 @@ fn rewrite_struct_lit<'a>(
             nested_shape,
             tactic,
             context,
-            force_no_trailing_comma
-                || has_base
-                || !context.use_block_indent()
-                || matches!(struct_rest, ast::StructRest::Rest(_)),
+            force_no_trailing_comma || has_base_or_rest || !context.use_block_indent(),
         );
 
         write_list(&item_vec, &fmt)?

tests/source/issue-4926/deeply_nested_struct.rs

@@ -0,0 +1,35 @@
+
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    a: i32,
+    b: i32,
+    c: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X { a: 1_000, b: 1_000, .. }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}

tests/source/issue-4926/deeply_nested_struct_with_long_field_names.rs

@@ -0,0 +1,43 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    really_really_long_field_a: i32,
+    really_really_really_long_field_b: i32,
+    really_really_really_really_long_field_c: i32,
+    really_really_really_really_really_long_field_d: i32,
+    really_really_really_really_really_really_long_field_e: i32,
+    f: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X {
+                                        really_really_long_field_a: 10,
+                                        really_really_really_long_field_b: 10,
+                                        really_really_really_really_long_field_c: 10,
+                                        really_really_really_really_really_long_field_d: 10,
+                                        really_really_really_really_really_really_long_field_e: 10, ..
+                                    }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}

tests/source/issue-4926/deeply_nested_struct_with_many_fields.rs

@@ -0,0 +1,44 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    a: i32,
+    b: i32,
+    c: i32,
+    d: i32,
+    e: i32,
+    f: i32,
+    g: i32,
+    h: i32,
+    i: i32,
+    j: i32,
+    k: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X {
+                                        a: 1_000, b: 1_000, c: 1_000, d: 1_000, e: 1_000, f: 1_000, g: 1_000, h: 1_000, i: 1_000, j: 1_000, ..
+                                    }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}

tests/source/issue-4926/enum_struct_field.rs

@@ -0,0 +1,35 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-enum_discrim_align_threshold: 30
+// rustfmt-imports_layout: HorizontalVertical
+
+#[derive(Default)]
+struct InnerStructA { bbbbbbbbb: i32, cccccccc: i32 }
+
+enum SomeEnumNamedD {
+    E(InnerStructA),
+    F {
+        ggggggggggggggggggggggggg: bool,
+        h: bool,
+    }
+}
+
+impl SomeEnumNamedD {
+    fn f_variant() -> Self {
+        Self::F { ggggggggggggggggggggggggg: true, h: true }
+    }
+}
+
+fn main() {
+    let kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk = SomeEnumNamedD::f_variant();
+    let something_we_care_about = matches!(
+        kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk,
+        SomeEnumNamedD::F {
+            ggggggggggggggggggggggggg: true,
+            ..
+        }
+    );
+
+    if something_we_care_about {
+        println!("Yup it happened");
+    }
+}

tests/source/issue-4926/minimum_example.rs

@@ -0,0 +1,10 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X { a: i32, b: i32 }
+
+fn test(x: X) {
+    let y = matches!(x, X {
+        a: 1,
+        ..
+    });
+}

tests/source/issue-4926/struct_with_long_field_names.rs

@@ -0,0 +1,21 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    really_really_long_field_a: i32,
+    really_really_really_long_field_b: i32,
+    really_really_really_really_long_field_c: i32,
+    really_really_really_really_really_long_field_d: i32,
+    really_really_really_really_really_really_long_field_e: i32,
+    f: i32,
+}
+
+fn test(x: X) {
+    let y = matches!(x, X {
+        really_really_long_field_a: 10,
+        really_really_really_long_field_b: 10,
+        really_really_really_really_long_field_c: 10,
+        really_really_really_really_really_long_field_d: 10,
+        really_really_really_really_really_really_long_field_e: 10,
+        ..
+    });
+}

tests/source/issue-4926/struct_with_many_fields.rs

@@ -0,0 +1,21 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    a: i32,
+    b: i32,
+    c: i32,
+    d: i32,
+    e: i32,
+    f: i32,
+    g: i32,
+    h: i32,
+    i: i32,
+    j: i32,
+    k: i32,
+}
+
+fn test(x: X) {
+    let y = matches!(x, X {
+        a: 1_000, b: 1_000, c: 1_000, d: 1_000, e: 1_000, f: 1_000, g: 1_000, h: 1_000, i: 1_000, j: 1_000, ..
+    });
+}

tests/target/issue-4926/deeply_nested_struct.rs

@@ -0,0 +1,38 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    a: i32,
+    b: i32,
+    c: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X {
+                                        a: 1_000,
+                                        b: 1_000,
+                                        ..
+                                    }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}

tests/target/issue-4926/deeply_nested_struct_with_long_field_names.rs

@@ -0,0 +1,44 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    really_really_long_field_a: i32,
+    really_really_really_long_field_b: i32,
+    really_really_really_really_long_field_c: i32,
+    really_really_really_really_really_long_field_d: i32,
+    really_really_really_really_really_really_long_field_e: i32,
+    f: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X {
+                                        really_really_long_field_a: 10,
+                                        really_really_really_long_field_b: 10,
+                                        really_really_really_really_long_field_c: 10,
+                                        really_really_really_really_really_long_field_d: 10,
+                                        really_really_really_really_really_really_long_field_e: 10,
+                                        ..
+                                    }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}

tests/target/issue-4926/deeply_nested_struct_with_many_fields.rs

@@ -0,0 +1,54 @@
+// rustfmt-struct_field_align_threshold: 30
+
+struct X {
+    a: i32,
+    b: i32,
+    c: i32,
+    d: i32,
+    e: i32,
+    f: i32,
+    g: i32,
+    h: i32,
+    i: i32,
+    j: i32,
+    k: i32,
+}
+
+fn test(x: X) {
+    let d = {
+        let e = {
+            let f = {
+                let g = {
+                    let h = {
+                        let i = {
+                            let j = {
+                                matches!(
+                                    x,
+                                    X {
+                                        a: 1_000,
+                                        b: 1_000,
+                                        c: 1_000,
+                                        d: 1_000,
+                                        e: 1_000,
+                                        f: 1_000,
+                                        g: 1_000,
+                                        h: 1_000,
+                                        i: 1_000,
+                                        j: 1_000,
+                                        ..
+                                    }
+                                )
+                            };
+                            j
+                        };
+                        i
+                    };
+                    h
+                };
+                g
+            };
+            f
+        };
+        e
+    };
+}