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Merge #256
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256: Improve/add use_item documentation r=matklad a=DJMcNab

Adds some documentation to use_item explaining all code paths (use imports are hard, especially with the ongoing discussion of anchored v. uniform paths - see rust-lang/rust#55618 for what appears to be the latest developments)

Co-authored-by: DJMcNab <36049421+djmcnab@users.noreply.github.com>
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@bors @DJMcNab
bors[bot] and DJMcNab committed Dec 6, 2018
2 parents 7ff6121 + 455ef94 commit 25cf234
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Showing 11 changed files with 467 additions and 1 deletion.
55 changes: 54 additions & 1 deletion crates/ra_syntax/src/grammar/items/use_item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,25 +7,75 @@ pub(super) fn use_item(p: &mut Parser) {
p.expect(SEMI);
}

/// Parse a use 'tree', such as `some::path` in `use some::path;`
/// Note that this is called both by `use_item` and `use_tree_list`,
/// so handles both `some::path::{inner::path}` and `inner::path` in
/// `use some::path::{inner::path};`
fn use_tree(p: &mut Parser) {
let la = p.nth(1);
let m = p.start();
match (p.current(), la) {
// Finish the use_tree for cases of e.g.
// `use some::path::{self, *};` or `use *;`
// This does not handle cases such as `use some::path::*`
// N.B. in Rust 2015 `use *;` imports all from crate root
// however in Rust 2018 `use *;` errors: ('cannot glob-import all possible crates')
// TODO: Add this error (if not out of scope)

// test use_star
// use *;
// use ::*;
// use some::path::{*};
// use some::path::{::*};
(STAR, _) => p.bump(),
(COLONCOLON, STAR) => {
// Parse `use ::*;`, which imports all from the crate root in Rust 2015
// This is invalid inside a use_tree_list, (e.g. `use some::path::{::*}`)
// but still parses and errors later: ('crate root in paths can only be used in start position')
// TODO: Add this error (if not out of scope)
// In Rust 2018, it is always invalid (see above)
p.bump();
p.bump();
}
// Open a use tree list
// Handles cases such as `use {some::path};` or `{inner::path}` in
// `use some::path::{{inner::path}, other::path}`

// test use_tree_list
// use {crate::path::from::root, or::path::from::crate_name}; // Rust 2018 (with a crate named `or`)
// use {path::from::root}; // Rust 2015
// use ::{some::arbritrary::path}; // Rust 2015
// use ::{{{crate::export}}}; // Nonsensical but perfectly legal nestnig
(L_CURLY, _) | (COLONCOLON, L_CURLY) => {
if p.at(COLONCOLON) {
p.bump();
}
use_tree_list(p);
}
// Parse a 'standard' path.
// Also handles aliases (e.g. `use something as something_else`)

// test use_path
// use ::crate_name; // Rust 2018 - All flavours
// use crate_name; // Rust 2018 - Anchored paths
// use item_in_scope_or_crate_name; // Rust 2018 - Uniform Paths
//
// use self::module::Item;
// use crate::Item;
// use self::some::Struct;
// use crate_name::some_item;
_ if paths::is_path_start(p) => {
paths::use_path(p);
match p.current() {
AS_KW => {
// test use_alias
// use some::path as some_name;
// use some::{
// other::path as some_other_name,
// different::path as different_name,
// yet::another::path,
// running::out::of::synonyms::for::different::*
// };
opt_alias(p);
}
COLONCOLON => {
Expand All @@ -34,6 +84,9 @@ fn use_tree(p: &mut Parser) {
STAR => {
p.bump();
}
// test use_tree_list_after_path
// use crate::{Item};
// use self::{Item};
L_CURLY => use_tree_list(p),
_ => {
// is this unreachable?
Expand All @@ -46,7 +99,7 @@ fn use_tree(p: &mut Parser) {
}
_ => {
m.abandon(p);
p.err_and_bump("expected one of `*`, `::`, `{`, `self`, `super`, `indent`");
p.err_and_bump("expected one of `*`, `::`, `{`, `self`, `super` or an indentifier");
return;
}
}
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3 changes: 3 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0114_use_path.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
use ::crate_name; // Rust 2018 - All flavours
use crate_name; // Rust 2018 - Anchored paths
use item_in_scope_or_crate_name; // Rust 2018 - Uniform Paths
38 changes: 38 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0114_use_path.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
SOURCE_FILE@[0; 154)
USE_ITEM@[0; 17)
USE_KW@[0; 3)
WHITESPACE@[3; 4)
USE_TREE@[4; 16)
PATH@[4; 16)
PATH_SEGMENT@[4; 16)
COLONCOLON@[4; 6)
NAME_REF@[6; 16)
IDENT@[6; 16) "crate_name"
SEMI@[16; 17)
WHITESPACE@[17; 18)
COMMENT@[18; 45)
WHITESPACE@[45; 46)
USE_ITEM@[46; 61)
USE_KW@[46; 49)
WHITESPACE@[49; 50)
USE_TREE@[50; 60)
PATH@[50; 60)
PATH_SEGMENT@[50; 60)
NAME_REF@[50; 60)
IDENT@[50; 60) "crate_name"
SEMI@[60; 61)
WHITESPACE@[61; 62)
COMMENT@[62; 91)
WHITESPACE@[91; 92)
USE_ITEM@[92; 124)
USE_KW@[92; 95)
WHITESPACE@[95; 96)
USE_TREE@[96; 123)
PATH@[96; 123)
PATH_SEGMENT@[96; 123)
NAME_REF@[96; 123)
IDENT@[96; 123) "item_in_scope_or_crate_name"
SEMI@[123; 124)
WHITESPACE@[124; 125)
COMMENT@[125; 153)
WHITESPACE@[153; 154)
7 changes: 7 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0115_use_alias.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
use some::path as some_name;
use some::{
other::path as some_other_name,
different::path as different_name,
yet::another::path,
running::out::of::synonyms::for::different::*
};
124 changes: 124 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0115_use_alias.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,124 @@
SOURCE_FILE@[0; 181)
USE_ITEM@[0; 28)
USE_KW@[0; 3)
WHITESPACE@[3; 4)
USE_TREE@[4; 27)
PATH@[4; 14)
PATH@[4; 8)
PATH_SEGMENT@[4; 8)
NAME_REF@[4; 8)
IDENT@[4; 8) "some"
COLONCOLON@[8; 10)
PATH_SEGMENT@[10; 14)
NAME_REF@[10; 14)
IDENT@[10; 14) "path"
WHITESPACE@[14; 15)
ALIAS@[15; 27)
AS_KW@[15; 17)
WHITESPACE@[17; 18)
NAME@[18; 27)
IDENT@[18; 27) "some_name"
SEMI@[27; 28)
WHITESPACE@[28; 29)
USE_ITEM@[29; 180)
USE_KW@[29; 32)
WHITESPACE@[32; 33)
USE_TREE@[33; 179)
PATH@[33; 37)
PATH_SEGMENT@[33; 37)
NAME_REF@[33; 37)
IDENT@[33; 37) "some"
COLONCOLON@[37; 39)
USE_TREE_LIST@[39; 179)
L_CURLY@[39; 40)
WHITESPACE@[40; 42)
USE_TREE@[42; 72)
PATH@[42; 53)
PATH@[42; 47)
PATH_SEGMENT@[42; 47)
NAME_REF@[42; 47)
IDENT@[42; 47) "other"
COLONCOLON@[47; 49)
PATH_SEGMENT@[49; 53)
NAME_REF@[49; 53)
IDENT@[49; 53) "path"
WHITESPACE@[53; 54)
ALIAS@[54; 72)
AS_KW@[54; 56)
WHITESPACE@[56; 57)
NAME@[57; 72)
IDENT@[57; 72) "some_other_name"
COMMA@[72; 73)
WHITESPACE@[73; 75)
USE_TREE@[75; 108)
PATH@[75; 90)
PATH@[75; 84)
PATH_SEGMENT@[75; 84)
NAME_REF@[75; 84)
IDENT@[75; 84) "different"
COLONCOLON@[84; 86)
PATH_SEGMENT@[86; 90)
NAME_REF@[86; 90)
IDENT@[86; 90) "path"
WHITESPACE@[90; 91)
ALIAS@[91; 108)
AS_KW@[91; 93)
WHITESPACE@[93; 94)
NAME@[94; 108)
IDENT@[94; 108) "different_name"
COMMA@[108; 109)
WHITESPACE@[109; 111)
USE_TREE@[111; 129)
PATH@[111; 129)
PATH@[111; 123)
PATH@[111; 114)
PATH_SEGMENT@[111; 114)
NAME_REF@[111; 114)
IDENT@[111; 114) "yet"
COLONCOLON@[114; 116)
PATH_SEGMENT@[116; 123)
NAME_REF@[116; 123)
IDENT@[116; 123) "another"
COLONCOLON@[123; 125)
PATH_SEGMENT@[125; 129)
NAME_REF@[125; 129)
IDENT@[125; 129) "path"
COMMA@[129; 130)
WHITESPACE@[130; 132)
USE_TREE@[132; 177)
PATH@[132; 174)
PATH@[132; 163)
PATH@[132; 158)
PATH@[132; 148)
PATH@[132; 144)
PATH@[132; 139)
PATH_SEGMENT@[132; 139)
NAME_REF@[132; 139)
IDENT@[132; 139) "running"
COLONCOLON@[139; 141)
PATH_SEGMENT@[141; 144)
NAME_REF@[141; 144)
IDENT@[141; 144) "out"
COLONCOLON@[144; 146)
PATH_SEGMENT@[146; 148)
NAME_REF@[146; 148)
IDENT@[146; 148) "of"
COLONCOLON@[148; 150)
PATH_SEGMENT@[150; 158)
NAME_REF@[150; 158)
IDENT@[150; 158) "synonyms"
COLONCOLON@[158; 160)
err: `expected identifier`
PATH_SEGMENT@[160; 163)
ERROR@[160; 163)
FOR_KW@[160; 163)
COLONCOLON@[163; 165)
PATH_SEGMENT@[165; 174)
NAME_REF@[165; 174)
IDENT@[165; 174) "different"
COLONCOLON@[174; 176)
STAR@[176; 177)
WHITESPACE@[177; 178)
R_CURLY@[178; 179)
SEMI@[179; 180)
WHITESPACE@[180; 181)
4 changes: 4 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0116_use_star.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
use *;
use ::*;
use some::path::{*};
use some::path::{::*};
59 changes: 59 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0116_use_star.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,59 @@
SOURCE_FILE@[0; 60)
USE_ITEM@[0; 6)
USE_KW@[0; 3)
WHITESPACE@[3; 4)
USE_TREE@[4; 5)
STAR@[4; 5)
SEMI@[5; 6)
WHITESPACE@[6; 7)
USE_ITEM@[7; 15)
USE_KW@[7; 10)
WHITESPACE@[10; 11)
USE_TREE@[11; 14)
COLONCOLON@[11; 13)
STAR@[13; 14)
SEMI@[14; 15)
WHITESPACE@[15; 16)
USE_ITEM@[16; 36)
USE_KW@[16; 19)
WHITESPACE@[19; 20)
USE_TREE@[20; 35)
PATH@[20; 30)
PATH@[20; 24)
PATH_SEGMENT@[20; 24)
NAME_REF@[20; 24)
IDENT@[20; 24) "some"
COLONCOLON@[24; 26)
PATH_SEGMENT@[26; 30)
NAME_REF@[26; 30)
IDENT@[26; 30) "path"
COLONCOLON@[30; 32)
USE_TREE_LIST@[32; 35)
L_CURLY@[32; 33)
USE_TREE@[33; 34)
STAR@[33; 34)
R_CURLY@[34; 35)
SEMI@[35; 36)
WHITESPACE@[36; 37)
USE_ITEM@[37; 59)
USE_KW@[37; 40)
WHITESPACE@[40; 41)
USE_TREE@[41; 58)
PATH@[41; 51)
PATH@[41; 45)
PATH_SEGMENT@[41; 45)
NAME_REF@[41; 45)
IDENT@[41; 45) "some"
COLONCOLON@[45; 47)
PATH_SEGMENT@[47; 51)
NAME_REF@[47; 51)
IDENT@[47; 51) "path"
COLONCOLON@[51; 53)
USE_TREE_LIST@[53; 58)
L_CURLY@[53; 54)
USE_TREE@[54; 57)
COLONCOLON@[54; 56)
STAR@[56; 57)
R_CURLY@[57; 58)
SEMI@[58; 59)
WHITESPACE@[59; 60)
2 changes: 2 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0117_use_tree_list_after_path.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
use crate::{Item};
use self::{Item};
37 changes: 37 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0117_use_tree_list_after_path.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
SOURCE_FILE@[0; 37)
USE_ITEM@[0; 18)
USE_KW@[0; 3)
WHITESPACE@[3; 4)
USE_TREE@[4; 17)
PATH@[4; 9)
PATH_SEGMENT@[4; 9)
CRATE_KW@[4; 9)
COLONCOLON@[9; 11)
USE_TREE_LIST@[11; 17)
L_CURLY@[11; 12)
USE_TREE@[12; 16)
PATH@[12; 16)
PATH_SEGMENT@[12; 16)
NAME_REF@[12; 16)
IDENT@[12; 16) "Item"
R_CURLY@[16; 17)
SEMI@[17; 18)
WHITESPACE@[18; 19)
USE_ITEM@[19; 36)
USE_KW@[19; 22)
WHITESPACE@[22; 23)
USE_TREE@[23; 35)
PATH@[23; 27)
PATH_SEGMENT@[23; 27)
SELF_KW@[23; 27)
COLONCOLON@[27; 29)
USE_TREE_LIST@[29; 35)
L_CURLY@[29; 30)
USE_TREE@[30; 34)
PATH@[30; 34)
PATH_SEGMENT@[30; 34)
NAME_REF@[30; 34)
IDENT@[30; 34) "Item"
R_CURLY@[34; 35)
SEMI@[35; 36)
WHITESPACE@[36; 37)
4 changes: 4 additions & 0 deletions crates/ra_syntax/tests/data/parser/inline/0118_use_tree_list.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
use {crate::path::from::root, or::path::from::crate_name}; // Rust 2018 (with a crate named `or`)
use {path::from::root}; // Rust 2015
use ::{some::arbritrary::path}; // Rust 2015
use ::{{{crate::export}}}; // Nonsensical but perfectly legal nestnig
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