mirror of https://github.com/rust-lang/rust
75 lines
2.3 KiB
Rust
75 lines
2.3 KiB
Rust
// issue: #110623
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//@ check-pass
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use std::{collections::BTreeMap, num::ParseIntError, str::FromStr};
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enum FileSystem {
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File(usize),
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Directory(BTreeMap<String, FileSystem>),
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}
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impl FromStr for FileSystem {
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type Err = ParseIntError;
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fn from_str(s: &str) -> Result<Self, Self::Err> {
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if s.starts_with("dir") {
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Ok(Self::new_dir())
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} else {
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Ok(Self::File(s.split_whitespace().next().unwrap().parse()?))
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}
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}
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}
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impl FileSystem {
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fn new_dir() -> FileSystem {
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FileSystem::Directory(BTreeMap::new())
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}
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fn insert(&mut self, name: String, other: FileSystem) -> Option<FileSystem> {
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match self {
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FileSystem::File(_) => panic!("can only insert into directory!"),
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FileSystem::Directory(tree) => tree.insert(name, other),
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}
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}
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// Recursively build a tree from commands. This uses (abuses?)
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// the fact that `cd /` only appears at the start and that
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// subsequent `cd`s can only move ONE level to use the recursion
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// stack as the filesystem stack
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fn build<'a>(
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&mut self,
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mut commands: impl Iterator<Item = &'a str> + 'a,
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) -> Option<impl Iterator<Item = &'a str> + 'a> {
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let cmd = commands.next()?;
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let mut elements = cmd.lines();
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match elements.next().map(str::trim) {
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Some("cd /") | None => self.build(commands),
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Some("cd ..") => {
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// return to higher scope
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Some(commands)
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}
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Some("ls") => {
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for item in elements {
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let name = item.split_whitespace().last().unwrap();
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let prior = self.insert(name.to_string(), item.parse().unwrap());
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debug_assert!(prior.is_none());
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}
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// continue on
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self.build(commands)
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}
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Some(other_cd) => {
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let name = other_cd
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.trim()
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.strip_prefix("cd ")
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.expect("expected a cd command");
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let mut directory = FileSystem::new_dir();
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let further_commands = directory.build(commands);
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self.insert(name.to_string(), directory);
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self.build(further_commands?) // THIS LINE FAILS TO COMPILE
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}
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}
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}
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}
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fn main() {}
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