refactor: soft deprecate match_arm_blocks in favour of match_arm_wrapping (rust-lang#4896)

Map `match_arm_blocks` option as `match_arm_wrapping` variants.

Author: ashvin021

Diff for: src/config/config_type.rs

@@ -106,6 +106,7 @@ macro_rules! create_config {
                     | "chain_width" => self.0.set_heuristics(),
                     "license_template_path" => self.0.set_license_template(),
                     "merge_imports" => self.0.set_merge_imports(),
+                    "match_arm_blocks" => self.0.set_match_arm_blocks(),
                     &_ => (),
                 }
             }
@@ -166,6 +167,7 @@ macro_rules! create_config {
                 self.set_license_template();
                 self.set_ignore(dir);
                 self.set_merge_imports();
+                self.set_match_arm_blocks();
                 self
             }
 
@@ -249,14 +251,16 @@ macro_rules! create_config {
                     | "chain_width" => self.set_heuristics(),
                     "license_template_path" => self.set_license_template(),
                     "merge_imports" => self.set_merge_imports(),
+                    "match_arm_blocks" => self.set_match_arm_blocks(),
                     &_ => (),
                 }
             }
 
             #[allow(unreachable_pub)]
             pub fn is_hidden_option(name: &str) -> bool {
-                const HIDE_OPTIONS: [&str; 5] =
-                    ["verbose", "verbose_diff", "file_lines", "width_heuristics", "merge_imports"];
+                const HIDE_OPTIONS: [&str; 6] =
+                    ["verbose", "verbose_diff", "file_lines", "width_heuristics", "merge_imports",
+                    "match_arm_blocks"];
                 HIDE_OPTIONS.contains(&name)
             }
 
@@ -421,6 +425,22 @@ macro_rules! create_config {
                 }
             }
 
+            fn set_match_arm_blocks(&mut self) {
+                if self.was_set().match_arm_blocks() {
+                    eprintln!(
+                        "Warning: the `match_arm_blocks` option is deprecated. \
+                        Use `match_arm_wrapping` instead"
+                    );
+                    if !self.was_set().match_arm_wrapping() {
+                        self.match_arm_wrapping.2 = if self.match_arm_blocks() {
+                            MatchArmWrapping::Default
+                        } else {
+                            MatchArmWrapping::NoBlockFirstLine
+                        };
+                    }
+                }
+            }
+
             #[allow(unreachable_pub)]
             /// Returns `true` if the config key was explicitly set and is the default value.
             pub fn is_default(&self, key: &str) -> bool {

Diff for: src/config/mod.rs

@@ -110,8 +110,9 @@ create_config! {
         "Align struct fields if their diffs fits within threshold";
     enum_discrim_align_threshold: usize, 0, false,
         "Align enum variants discrims, if their diffs fit within threshold";
-    match_arm_blocks: bool, true, false, "Wrap the body of arms in blocks when it does not fit on \
-        the same line with the pattern of arms";
+    match_arm_wrapping: MatchArmWrapping, MatchArmWrapping::Default, false,
+        "Wrap the body of match arms according to the given options";
+    match_arm_blocks: bool, true, false, "(deprecated: use match_arm_wrapping instead)";
     match_arm_leading_pipes: MatchArmLeadingPipe, MatchArmLeadingPipe::Never, true,
         "Determines whether leading pipes are emitted on match arms";
     force_multiline_blocks: bool, false, false,
@@ -426,6 +427,11 @@ mod test {
                 "Merge imports";
             merge_imports: bool, false, false, "(deprecated: use imports_granularity instead)";
 
+            // match_arm_blocks deprecation
+            match_arm_blocks: bool, true, false, "(deprecated: use match_arm_wrapping instead)";
+            match_arm_wrapping: MatchArmWrapping, MatchArmWrapping::Default, false,
+                "Wrap the body of match arms according to the given options";
+
             // Width Heuristics
             use_small_heuristics: Heuristics, Heuristics::Default, true,
                 "Whether to use different formatting for items and \
@@ -590,6 +596,7 @@ combine_control_expr = true
 overflow_delimited_expr = false
 struct_field_align_threshold = 0
 enum_discrim_align_threshold = 0
+match_arm_wrapping = "Default"
 match_arm_blocks = true
 match_arm_leading_pipes = "Never"
 force_multiline_blocks = false

Diff for: src/config/options.rs

@@ -442,3 +442,12 @@ pub enum MatchArmLeadingPipe {
     /// Preserve any existing leading pipes
     Preserve,
 }
+
+/// Controls wrapping for match arm bodies
+#[config_type]
+pub enum MatchArmWrapping {
+    /// Follow the Style Guide Prescription
+    Default,
+    /// Don't block wrap when the first line can't fit
+    NoBlockFirstLine,
+}

Diff for: src/matches.rs

@@ -7,7 +7,9 @@ use rustc_span::{BytePos, Span};
 
 use crate::comment::{combine_strs_with_missing_comments, rewrite_comment};
 use crate::config::lists::*;
-use crate::config::{Config, ControlBraceStyle, IndentStyle, MatchArmLeadingPipe, Version};
+use crate::config::{
+    Config, ControlBraceStyle, IndentStyle, MatchArmLeadingPipe, MatchArmWrapping, Version,
+};
 use crate::expr::{
     format_expr, is_empty_block, is_simple_block, is_unsafe_block, prefer_next_line, rewrite_cond,
     ExprType, RhsTactics,
@@ -413,26 +415,28 @@ fn rewrite_match_body(
         }
 
         let indent_str = shape.indent.to_string_with_newline(context.config);
-        let (body_prefix, body_suffix) =
-            if context.config.match_arm_blocks() && !context.inside_macro() {
-                let comma = if context.config.match_block_trailing_comma() {
-                    ","
+        let (body_prefix, body_suffix) = if context.config.match_arm_wrapping()
+            == MatchArmWrapping::Default
+            && !context.inside_macro()
+        {
+            let comma = if context.config.match_block_trailing_comma() {
+                ","
+            } else {
+                ""
+            };
+            let semicolon = if context.config.version() == Version::One {
+                ""
+            } else {
+                if semicolon_for_expr(context, body) {
+                    ";"
                 } else {
                     ""
-                };
-                let semicolon = if context.config.version() == Version::One {
-                    ""
-                } else {
-                    if semicolon_for_expr(context, body) {
-                        ";"
-                    } else {
-                        ""
-                    }
-                };
-                ("{", format!("{}{}}}{}", semicolon, indent_str, comma))
-            } else {
-                ("", String::from(","))
+                }
             };
+            ("{", format!("{}{}}}{}", semicolon, indent_str, comma))
+        } else {
+            ("", String::from(","))
+        };
 
         let block_sep = match context.config.control_brace_style() {
             ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),