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refactor and document the chain reformatting code

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This commit is contained in:
Nick Cameron 2016-04-22 13:36:27 +12:00
parent 4c3228530f
commit 3d46532e72
2 changed files with 201 additions and 79 deletions
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276
src/chains.rs
View file

@ -8,16 +8,88 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Formatting of chained expressions, i.e. expressions which are chained by
// dots: struct and enum field access and method calls.
//
// Instead of walking these subexpressions one-by-one, as is our usual strategy
// for expression formatting, we collect maximal sequences of these expressions
// and handle them simultaneously.
//
// Whenever possible, the entire chain is put on a single line. If that fails,
// we put each subexpression on a separate, much like the (default) function
// argument function argument strategy.
/// Formatting of chained expressions, i.e. expressions which are chained by
/// dots: struct and enum field access and method calls.
///
/// Instead of walking these subexpressions one-by-one, as is our usual strategy
/// for expression formatting, we collect maximal sequences of these expressions
/// and handle them simultaneously.
///
/// Whenever possible, the entire chain is put on a single line. If that fails,
/// we put each subexpression on a separate, much like the (default) function
/// argument function argument strategy.
///
/// Depends on config options: `chain_base_indent` is the indent to use for
/// blocks in the parent/root/base of the chain.
/// E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
/// following values of `chain_base_indent`:
/// Visual:
/// ```
/// let foo = {
/// aaaa;
/// bbb;
/// ccc
/// }
/// .bar
/// .baz();
/// ```
/// Inherit:
/// ```
/// let foo = {
/// aaaa;
/// bbb;
/// ccc
/// }
/// .bar
/// .baz();
/// ```
/// Tabbed:
/// ```
/// let foo = {
/// aaaa;
/// bbb;
/// ccc
/// }
/// .bar
/// .baz();
/// ```
///
/// `chain_indent` dictates how the rest of the chain is aligned. This only seems
/// to have an effect if the first non-root part of the chain is put on a
/// newline, otherwise we align the dots:
/// ```
/// foo.bar
/// .baz()
/// ```
/// If the first item in the chain is a block expression, we align the dots with
/// the braces.
///
/// Otherwise:
/// Visual:
/// ```
/// let a = foo(aaa, bbb)
/// .bar
/// .baz()
/// ```
/// Visual seems to be a tab indented from the indent of the whole expression.
/// Inherit:
/// ```
/// let a = foo(aaa, bbb)
/// .bar
/// .baz()
/// ```
/// Tabbed:
/// ```
/// let a = foo(aaa, bbb)
/// .bar
/// .baz()
/// ```
/// `chains_overflow_last` applies only to chains where the last item is a
/// method call. Usually, any line break in a chain sub-expression causes the
/// whole chain to be split with newlines at each `.`. With `chains_overflow_last`
/// true, then we allow the last method call to spill over multiple lines without
/// forcing the rest of the chain to be split.
use Indent;
use rewrite::{Rewrite, RewriteContext};
@ -28,49 +100,43 @@ use config::BlockIndentStyle;
use syntax::{ast, ptr};
use syntax::codemap::{mk_sp, Span};
pub fn rewrite_chain(mut expr: &ast::Expr,
pub fn rewrite_chain(expr: &ast::Expr,
context: &RewriteContext,
width: usize,
offset: Indent)
-> Option<String> {
let total_span = expr.span;
let mut subexpr_list = vec![expr];
let (parent, subexpr_list) = make_subexpr_list(expr);
while let Some(subexpr) = pop_expr_chain(expr) {
subexpr_list.push(subexpr);
expr = subexpr;
}
let parent_block_indent = match context.config.chain_base_indent {
BlockIndentStyle::Visual => offset,
BlockIndentStyle::Inherit => context.block_indent,
BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
};
// Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
let parent_block_indent = chain_base_indent(context, offset);
let parent_context = &RewriteContext { block_indent: parent_block_indent, ..*context };
let parent = subexpr_list.pop().unwrap();
let parent_rewrite = try_opt!(expr.rewrite(parent_context, width, offset));
let parent_rewrite = try_opt!(parent.rewrite(parent_context, width, offset));
// Decide how to layout the rest of the chain. `extend` is true if we can
// put the first non-parent item on the same line as the parent.
let (indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(parent) ||
parent_rewrite.len() <= context.config.tab_spaces {
// Try and put the whole chain on one line.
(offset + Indent::new(0, parent_rewrite.len()), true)
} else if is_block_expr(parent, &parent_rewrite) {
// The parent is a block, so align the rest of the chain with the closing
// brace.
(parent_block_indent, false)
} else {
match context.config.chain_indent {
BlockIndentStyle::Inherit => (context.block_indent, false),
BlockIndentStyle::Tabbed => (context.block_indent.block_indent(context.config), false),
BlockIndentStyle::Visual => (offset + Indent::new(context.config.tab_spaces, 0), false),
}
(chain_indent(context, offset), false)
};
let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
let mut rewrites = try_opt!(subexpr_list.iter()
.rev()
.map(|e| {
rewrite_chain_expr(e,
total_span,
context,
max_width,
indent)
rewrite_chain_subexpr(e,
total_span,
context,
max_width,
indent)
})
.collect::<Option<Vec<_>>>());
@ -80,6 +146,7 @@ pub fn rewrite_chain(mut expr: &ast::Expr,
.fold(0, |a, b| a + first_line_width(b)) +
parent_rewrite.len();
let total_width = almost_total + first_line_width(rewrites.last().unwrap());
let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
// Look at the source code. Unless all chain elements start on the same
// line, we won't consider putting them on a single line either.
@ -92,49 +159,40 @@ pub fn rewrite_chain(mut expr: &ast::Expr,
false
};
let fits_single_line = !veto_single_line &&
match subexpr_list[0].node {
ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions)
if context.config.chains_overflow_last => {
let len = rewrites.len();
let (init, last) = rewrites.split_at_mut(len - 1);
let last = &mut last[0];
let mut fits_single_line = !veto_single_line && total_width <= width;
if fits_single_line {
let len = rewrites.len();
let (init, last) = rewrites.split_at_mut(len - 1);
fits_single_line = init.iter().all(|s| !s.contains('\n'));
if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
let last_rewrite = width.checked_sub(almost_total)
.and_then(|inner_width| {
rewrite_method_call(method_name.node,
types,
expressions,
total_span,
context,
inner_width,
offset + almost_total)
});
match last_rewrite {
Some(mut string) => {
::std::mem::swap(&mut string, last);
true
}
None => false,
if fits_single_line {
fits_single_line = match expr.node {
ref e @ ast::ExprKind::MethodCall(..) if context.config.chains_overflow_last => {
rewrite_method_call_with_overflow(e,
&mut last[0],
almost_total,
width,
total_span,
context,
offset)
}
} else {
false
_ => !last[0].contains('\n'),
}
}
_ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
};
}
let connector = if fits_single_line && !parent_rewrite.contains('\n') {
// Yay, we can put everything on one line.
String::new()
} else {
// Use new lines.
format!("\n{}", indent.to_string(context.config))
};
let first_connector = if extend {
""
} else {
&connector[..]
&connector
};
wrap_str(format!("{}{}{}",
@ -146,8 +204,40 @@ pub fn rewrite_chain(mut expr: &ast::Expr,
offset)
}
fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
last: &mut String,
almost_total: usize,
width: usize,
total_span: Span,
context: &RewriteContext,
offset: Indent)
-> bool {
if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
let budget = match width.checked_sub(almost_total) {
Some(b) => b,
None => return false,
};
let mut last_rewrite = rewrite_method_call(method_name.node,
types,
expressions,
total_span,
context,
budget,
offset + almost_total);
if let Some(ref mut s) = last_rewrite {
::std::mem::swap(s, last);
true
} else {
false
}
} else {
unreachable!();
}
}
// States whether an expression's last line exclusively consists of closing
// parens, braces and brackets in its idiomatic formatting.
// parens, braces, and brackets in its idiomatic formatting.
fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
match expr.node {
ast::ExprKind::Struct(..) |
@ -167,21 +257,53 @@ fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
}
}
fn pop_expr_chain(expr: &ast::Expr) -> Option<&ast::Expr> {
match expr.node {
ast::ExprKind::MethodCall(_, _, ref expressions) => Some(&expressions[0]),
ast::ExprKind::TupField(ref subexpr, _) |
ast::ExprKind::Field(ref subexpr, _) => Some(subexpr),
_ => None,
// Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
// E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
fn make_subexpr_list(mut expr: &ast::Expr) -> (&ast::Expr, Vec<&ast::Expr>) {
fn pop_expr_chain(expr: &ast::Expr) -> Option<&ast::Expr> {
match expr.node {
ast::ExprKind::MethodCall(_, _, ref expressions) => Some(&expressions[0]),
ast::ExprKind::TupField(ref subexpr, _) |
ast::ExprKind::Field(ref subexpr, _) => Some(subexpr),
_ => None,
}
}
let mut subexpr_list = vec![expr];
while let Some(subexpr) = pop_expr_chain(expr) {
subexpr_list.push(subexpr);
expr = subexpr;
}
let parent = subexpr_list.pop().unwrap();
(parent, subexpr_list)
}
fn chain_base_indent(context: &RewriteContext, offset: Indent) -> Indent {
match context.config.chain_base_indent {
BlockIndentStyle::Visual => offset,
BlockIndentStyle::Inherit => context.block_indent,
BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
}
}
fn rewrite_chain_expr(expr: &ast::Expr,
span: Span,
context: &RewriteContext,
width: usize,
offset: Indent)
-> Option<String> {
fn chain_indent(context: &RewriteContext, offset: Indent) -> Indent {
match context.config.chain_indent {
BlockIndentStyle::Inherit => context.block_indent,
BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
BlockIndentStyle::Visual => offset + Indent::new(context.config.tab_spaces, 0),
}
}
// Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
// `.c`.
fn rewrite_chain_subexpr(expr: &ast::Expr,
span: Span,
context: &RewriteContext,
width: usize,
offset: Indent)
-> Option<String> {
match expr.node {
ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
let inner = &RewriteContext { block_indent: offset, ..*context };
@ -213,7 +335,7 @@ fn rewrite_chain_expr(expr: &ast::Expr,
}
}
// Determines we can continue formatting a given expression on the same line.
// Determines if we can continue formatting a given expression on the same line.
fn is_continuable(expr: &ast::Expr) -> bool {
match expr.node {
ast::ExprKind::Path(..) => true,

4
src/config.rs
View file

@ -377,11 +377,11 @@ create_config! {
"Report all, none or unnumbered occurrences of FIXME in source file comments";
chain_base_indent: BlockIndentStyle, BlockIndentStyle::Visual, "Indent on chain base";
chain_indent: BlockIndentStyle, BlockIndentStyle::Visual, "Indentation of chain";
chains_overflow_last: bool, true, "Allow last call in method chain to break the line";
reorder_imports: bool, false, "Reorder import statements alphabetically";
single_line_if_else: bool, false, "Put else on same line as closing brace for if statements";
format_strings: bool, true, "Format string literals where necessary";
force_format_strings: bool, false, "Always format string literals";
chains_overflow_last: bool, true, "Allow last call in method chain to break the line";
take_source_hints: bool, true, "Retain some formatting characteristics from the source code";
hard_tabs: bool, false, "Use tab characters for indentation, spaces for alignment";
wrap_comments: bool, false, "Break comments to fit on the line";
@ -390,7 +390,7 @@ create_config! {
match_block_trailing_comma: bool, false,
"Put a trailing comma after a block based match arm (non-block arms are not affected)";
match_wildcard_trailing_comma: bool, true, "Put a trailing comma after a wildcard arm";
closure_block_indent_threshold: isize, 4, "How many lines a closure must have before it is \
closure_block_indent_threshold: isize, -1, "How many lines a closure must have before it is \
block indented. -1 means never use block indent.";
write_mode: WriteMode, WriteMode::Replace,
"What Write Mode to use when none is supplied: Replace, Overwrite, Display, Diff, Coverage";