Buggy import path resolution in corner cases with remappings and base path

Inspired by https://github.com/ethereum/solidity/pull/9353.

The way the compiler resolves imports into actual filesystem paths is intuitive in simple cases but gets convoluted quickly when you take into account all the factors that can affect it: remappings, base path, various flavors of relative paths, special file names, etc. I checked how it works in corner cases and in a lot of them the beahavior is either buggy or at least does not work the way I would expect it to.

## Issues
This section lists problems I have identified. See the reference at the end of the post for detailed examples.

1. Base path is sometimes prepended to absolute paths.
    - Base path is prepended to source directory path in imports starting with `.` or `..`.
    - Base path is prepended to remapped absolute imports.
2. Imports starting with `.` or `..` are not always relative to the source directory
    - Absolute imports can be remapped into imports starting with `.` or `..` but they then become relative to the current working directory.
    - Base path replaces source directory in absolute imports remapped to relative imports starting with `.` or `..`.
        - It should behave the same way as relative imports starting with `..` or `..`.
    - Paths that become relative after stripping of `file://` are always relative to the current working directory.
        - This does not happen when base paths is used.
3. Using a relative path to the source file on the command line sometimes makes relative imports resolve to different paths than when using an absolute path.
    - Remapping of `.` and `..` works differently when the path to the source file given to the compiler is relative.
    - Remappings ignore any number of leading `.` and `..` segments when the path to the source file given to the compiler is relative.
4. Relative paths with `..` segments that go beyond filesystem root are silently replaced with valid ones.
    - Remappings ignore any number of leading `.` and `..` segments in imports going beyond the root directory.
    - Remappings ignore any number of leading `.` and `..` segments when the path to the source file given to the compiler is relative.
    - Relative imports going beyond root directory ignore `..` and are relative to the current working directory (or to the base directory when base path is used).
5. It's possible to remap some of the paths added implicitly to relative imports.
    - Parts of the path that `.` and `..` get resolved into can get remapped.
    - Source directory path can be remapped.
6. Not all prefixes can be remapped.
    - Leading `.` and `..` in imports cannot be remapped.
    - `file://` prefix as a whole cannot be remapped but its fragments can.
7. Special behavior of `<stdin>`.
    - A file called `<stdin>` from current working directory can only be imported if use of the standard input is not requested.
        - If a file called `<stdin>` exists and standard input was requested, importing it should be an error.
    - Behavior of `<stdin>` in general might be unintended though there's probably no harm in allowing it to be remapped.
8. Trailing slashes in imports are replaced with `/.` (unless they start with `.` or `..`).
    - They should either be stripped or replaced with a single slash.
9. Multiple remappings of the same prefix are ignored and the last one takes effect.

## Current path resolution behavior
This section is meant mostly as a reference. There's no need to read it all to understand the issue. Skimming the headers should give you a good picture of what is happening.

Use it to see examples of the problems I listed above or just the current behavior in specific cases.

### Common setup for all examples below
- File containing the imports: `/project/contract.sol`.
- Working directory: `/home/user/work/`.

### Simple imports
#### Absolute
```solidity
import "/tmp/code/token.sol";         // -> /tmp/code/token.sol
import "/tmp/code/../code/token.sol"; // -> /tmp/code/token.sol
```

#### Relative imports are relative to current working directory
```solidity
import "token/token.sol";     // -> /home/user/work/token/token.sol
import ".../token/token.sol"; // -> /home/user/work/.../token/token.sol
```

#### Relative imports starting with `.` or `..` are relative to the source directory
```solidity
import "./token/token.sol";          // -> /project/token/token.sol
import "../project/token/token.sol"; // -> /project/token/token.sol
```

#### Relative imports going beyond root directory ignore `..` and are relative to the current working directory
```solidity
import "token/token.sol";                  // -> /home/user/work/token/token.sol
import "../token/token.sol";               // -> /home/user/token/token.sol
import "../../token/token.sol";            // -> /home/token/token.sol
import "../../../token/token.sol";         // -> /token/token.sol
import "../../../../token/token.sol";      // -> /home/user/work/token/token.sol
import "../../../../../token/token.sol";   // -> /home/user/work/token/token.sol
import "../../.././../../token/token.sol"; // -> /home/user/work/token/token.sol
```

### Path Remapping

#### Absolute imports can be remapped
```solidity
// Remappings: /tmp/code=/usr/lib
import "/tmp/code/token.sol"; // -> /usr/lib/token.sol
```

#### Relative imports can be remapped
```solidity
// Remappings: token=contract
import "token/token.sol"; // -> /home/user/work/contract/token.sol
```

#### Relative imports can be remapped into absolute imports
```solidity
// Remappings: token=/usr/lib
import "token/token.sol"; // -> /usr/lib/token.sol
```

#### Absolute imports can be remapped into imports relative to the current working directory
```solidity
// Remappings: /usr/lib=contract
import "/usr/lib/token.sol"; // -> /home/user/work/contract/token.sol
```

#### Absolute imports can be remapped into imports starting with `.` or `..` but they are also relative to the current working directory
Normally imports starting with `.` or `..` are relative to the source directory.
```solidity
// Remappings: /usr/lib=./contract
import "/usr/lib/token.sol"; // -> /home/user/work/contract/token.sol
```

```solidity
// Remappings: /usr/lib=../contract
import "/usr/lib/token.sol"; // -> /home/user/contract/token.sol
```

#### Only prefix can be remapped
```solidity
// Remappings: /usr=/tmp /lib=/bin contracts=token token.sol=contract.sol
import "/usr/usr/lib/token.sol";                // -> /tmp/usr/lib/token.sol
import "contracts/contracts/usr/lib/token.sol"; // -> /home/user/work/token/contracts/usr/lib/token.sol
import "token.sol";                             // -> /home/user/work/contract.sol
```

#### The remapping with the longest matching prefix is used
```solidity
// Remappings: /usr=/project/dex /usr/lib=/project/token contracts=tokens contracts/token.sol=dex.sol
import "/usr/lib/contracts/token.sol"; // -> /project/token/contracts/token.sol
import "contracts/token.sol";          // -> /home/user/work/dex.sol
```

#### Remapping is not recursive
```solidity
// Remappings: /a=/b /b=/c /c=/a
import "/a/token.sol"; // -> /b/token.sol
```

#### The last remapping takes precedence
```solidity
// Remappings: /a=/b /a=/c /a=/d
import "/a/token.sol"; // -> /d/token.sol
```

#### Remappings do not have to match whole path segments
```solidity
// Remappings: /c=/k c=k
import "/contracts/contract.sol"; // -> /kontracts/contract.sol
import "contracts/contract.sol";  // -> /home/user/work/kontracts/contract.sol
```

#### Leading `.` and `..` in imports cannot be remapped
```solidity
// Remappings: .=/tmp
import "./token/token.sol";   // -> /project/token/token.sol
import "../token/token.sol";  // -> /project/token.sol
import ".../token/token.sol"; // -> /tmp../token/token.sol
```

```solidity
// Remappings: ./token=contract ../token=contract .../token=contract
import "./token/token.sol";   // -> /project/token/token.sol
import "../token/token.sol";  // -> /project/token.sol
import ".../token/token.sol"; // -> /home/user/work/contract/token.sol
```

#### Parts of the path that `.` and `..` get resolved into can get remapped
```solidity
// Remappings: /project=/tmp /token=/tmp /project/token.sol=/tmp/dex.sol
import "./token/token.sol";   // -> /tmp/token/token.sol
import "../token/token.sol";  // -> /tmp/token.sol
import "./token.sol";         // -> /tmp/dex.sol
```

#### Remapping of `.` and `..` works differently when the path to the source file given to the compiler is relative
This is one of the cases where the path to the **file containing imports** (specified on the compiler's command line) affects how the imports are resolved.

The effect is different depending on the locations of the source directory and the current working directory relative to each other.

##### Example: Current working directory is a prefix of the source directory
- Source file passed to the compiler: `../contract.sol`.
- Working directory: `/project/subdir/`.

```solidity
// Remappings: ./token=contract ../token=contract
import "./token/token.sol";   // -> /home/user/work/contract/token.sol
import "../token/token.sol";  // -> /home/user/work/token.sol
```

#### Paths are not canonicalized before remapping
```solidity
// Remappings: /tmp/code=/usr/lib token=contract
import "/tmp/../tmp/code/token.sol"; // -> /tmp/code/token.sol
import "code/../token/token.sol";    // -> /home/user/work/token/token.sol
```

#### Remappings ignore any number of leading `.` and `..` segments in imports going beyond the root directory
```solidity
// Remappings: token=contract
import "token/token.sol";                  // -> /home/user/work/contract/token.sol
import "../token/token.sol";               // -> /home/user/token/token.sol
import "../../token/token.sol";            // -> /home/token/token.sol
import "../../../token/token.sol";         // -> /token/token.sol
import "../../../../token/token.sol";      // -> /home/user/work/contract/token.sol
import "../../../../../token/token.sol";   // -> /home/user/work/contract/token.sol
import "../../.././../../token/token.sol"; // -> /home/user/work/contract/token.sol
```

#### Remappings ignore any number of leading `.` and `..` segments when the path to the source file given to the compiler is relative
The effect is different depending on the locations of the source directory and the current working directory relative to each other.

##### Example: Current working directory is a prefix of the source directory
- Source file passed to the compiler: `../contract.sol`.
- Working directory: `/project/subdir/`.

```solidity
// Remappings: token=contract
import "token/token.sol";                  // -> /home/user/work/contract/token.sol
import "../token/token.sol";               // -> /home/user/work/contract/token.sol
import "../../token/token.sol";            // -> /home/user/work/contract/token.sol
import "../../../token/token.sol";         // -> /home/user/work/contract/token.sol
import "../../../../token/token.sol";      // -> /home/user/work/contract/token.sol
import "../../../../../token/token.sol";   // -> /home/user/work/contract/token.sol
import "../../.././../../token/token.sol"; // -> /home/user/work/contract/token.sol
```

#### Current working directory path cannot be remapped
```solidity
// Remappings: /home/user/work=/workdir
import "token/token.sol"; // -> /home/user/work/token/token.sol
```

#### Source directory path can be remapped
```solidity
// Remappings: /project=/tmp
import "./token/token.sol";          // -> /tmp/token/token.sol
import "../project/token/token.sol"; // -> /tmp/token/token.sol
```

### Base Path

#### Base path does not affect absolute imports
```solidity
// Base path: /base
import "/tmp/code/token.sol";         // -> /tmp/code/token.sol
import "/tmp/code/../code/token.sol"; // -> /tmp/code/token.sol
```

#### Base path replaces current working directory in relative imports
```solidity
// Base path: /base
import "token/token.sol"; // -> /base/token/token.sol
```

#### Base path is prepended to source directory path in imports starting with `.` or `..`
```solidity
// Base path: /base
import "./token/token.sol";  // -> /base/project/token/token.sol
import "../token/token.sol"; // -> /base/token/token.sol
```

#### Relative imports going beyond root directory ignore `..` and are relative to the base directory
```solidity
// Base path: /base
import "token/token.sol";                  // -> /base/token/token.sol
import "../token/token.sol";               // -> /base/token/token.sol
import "../../token/token.sol";            // -> /base/token/token.sol
import "../../../token/token.sol";         // -> /base/token/token.sol
import "../../../../token/token.sol";      // -> /base/token/token.sol
import "../../../../../token/token.sol";   // -> /base/token/token.sol
import "../../.././../../token/token.sol"; // -> /base/token/token.sol
```

#### Base path is prepended to remapped absolute imports
```solidity
// Base path: /base
// Remappings: /tmp/code=/usr/lib
import "/tmp/code/token.sol"; // -> /base/usr/lib/token.sol
```

#### Base path replaces current working directory in remapped relative imports
```solidity
// Base path: /base
// Remappings: token=contract
import "token/token.sol"; // -> /base/contract/token.sol
```

#### Base path is prepended to relative imports remapped into absolute imports
```solidity
// Base path: /base
// Remappings: token=/usr/lib
import "token/token.sol"; // -> /base/usr/lib/token.sol
```

#### Base path replaces current working directory in absolute imports remapped to relative imports
```solidity
// Base path: /base
// Remappings: /usr/lib=contract
import "/usr/lib/token.sol"; // -> /base/contract/token.sol
```

#### Base path replaces source directory in absolute imports remapped to relative imports starting with `.` or `..`
Without remapping such imports are relative to the source directory, not the current working directory.
```solidity
// Base path: /base
// Remappings: /usr/lib=./contract
import "/usr/lib/token.sol"; // -> /base/contract/token.sol
```

```solidity
// Base path: /base
// Remappings: /usr/lib=../contract
import "/usr/lib/token.sol"; // -> /contract/token.sol
```

#### Parts of the path that `.` and `..` get resolved into can get remapped when base path is used and such remappings don't override the base path
```solidity
// Base path: /base
// Remappings: /project=/tmp /token=/tmp /project/token.sol=/tmp/dex.sol
import "./token/token.sol";   // -> /base/tmp/token/token.sol
import "../token/token.sol";  // -> /base/tmp/token.sol
import "./token.sol";         // -> /base/tmp/dex.sol
```

#### Base path cannot be remapped
```solidity
// Base path: /base
// Remappings: /base=/tmp
import "token/token.sol"; // -> /base/token/token.sol
```

#### Source directory path can be remapped even when base path is used
```solidity
// Base path: /base
// Remappings: /project=/tmp /base=/usr/lib
import "./token/token.sol";          // -> /base/tmp/token/token.sol
import "../project/token/token.sol"; // -> /base/tmp/token/token.sol
```

#### Relative base path is relative to the current working directory
```solidity
// Base path: base
import "token/token.sol";    // -> /home/user/work/base/token/token.sol
import "./token/token.sol";  // -> /home/user/work/base/project/token/token.sol
import "../token/token.sol"; // -> /home/user/work/base/token/token.sol
```

```solidity
// Base path: .
import "token/token.sol";    // -> /home/user/work/token/token.sol
import "./token/token.sol";  // -> /home/user/work/project/token/token.sol
import "../token/token.sol"; // -> /home/user/work/token/token.sol
```

```solidity
// Base path: ..
import "token/token.sol";    // -> /home/user/token/token.sol
import "./token/token.sol";  // -> /home/user/project/token/token.sol
import "../token/token.sol"; // -> /home/user/token/token.sol
```

### Standard input

#### Standard input can be used as if it was an actual file called `<stdin>` if requested
```solidity
// Command line: contains `-`
import "<stdin>"; // -> stdin
```

If there is an actual file called <stdin> in the current directory, it's ignored.

#### A file called `<stdin>` from current working directory can only be imported if use of the standard input is not requested.
```solidity
// Command line: does not contain `-`
import "<stdin>"; // -> /home/user/work/<stdin>
```

#### `<stdin>` can be remapped to a path when it represents standard input
```solidity
// Command line: contains `-`
// Remappings: <stdin>=/tmp/code/token.sol
import "<stdin>"; // -> /tmp/code/token.sol
```

#### `<stdin>` can be remapped to a path when it represents a file
```solidity
// Command line: does not contain `-`
// Remappings: <stdin>=/tmp/code/token.sol
import "<stdin>"; // -> /tmp/code/token.sol
```

#### Paths can be remapped to `<stdin>` when it represents standard input
```solidity
// Command line: contains `-`
// Remappings: /tmp/code/token.sol=<stdin>
import "/tmp/code/token.sol"; // -> stdin
```

#### Paths can be remapped to `<stdin>` when it represents a file
```solidity
// Command line: does not contain `-`
// Remappings: /tmp/code/token.sol=<stdin>
import "/tmp/code/token.sol"; // -> /home/user/work/<stdin>
```

#### Base path does not affect `<stdin>` when it represents standard input
```solidity
// Command line: contains `-`
// Base path: /base
import "<stdin>"; // -> stdin
```

#### Base path affects `<stdin>` when it does not represent standard input
```solidity
// Command line: does not contain `-`
// Base path: /base
import "<stdin>"; // -> /base/<stdin>
```

### Extra Slashes

#### Multiple slashes between path segments in imports are squashed into one
```solidity
import "/tmp//code/token.sol";   // -> /tmp/code/token.sol
import "/tmp////code/token.sol"; // -> /tmp/code/token.sol
```

#### Trailing slashes in imports are replaced with `/.`
```solidity
import "/tmp/code/token.sol/";    // -> /tmp/code/token.sol/.
import "/tmp/code/token.sol//";   // -> /tmp/code/token.sol/.
import "/tmp/code/token.sol////"; // -> /tmp/code/token.sol/.
```

#### Trailing slashes in relative imports that start with `.` or `..` imports are stripped
```solidity
import "./token/token.sol/";     // -> /project/token/token.sol
import "./token/token.sol//";    // -> /project/token/token.sol
import "./token/token.sol////";  // -> /project/token/token.sol
import "../token/token.sol/";    // -> /project/token.sol
import "../token/token.sol//";   // -> /project/token.sol
import "../token/token.sol////"; // -> /project/token.sol
```

#### Two Leading slashes in imports are preserved
```solidity
import "//tmp/code/token.sol";    // -> //tmp/code/token.sol
```

#### More than two Leading slashes in imports are squashed into one
```solidity
import "///tmp/code/token.sol";    // -> /tmp/code/token.sol
import "////tmp/code/token.sol";   // -> /tmp/code/token.sol
import "/////tmp/code/token.sol";  // -> /tmp/code/token.sol
```

#### Slashes after the leading `.` or `..` in relative imports are squashed into one
```solidity
import "./token/token.sol";      // -> /project/token/token.sol
import ".//token/token.sol";     // -> /project/token/token.sol
import ".///token/token.sol";    // -> /project/token/token.sol
import ".////token/token.sol";   // -> /project/token/token.sol
import "..//token/token.sol";    // -> /token/token.sol
import "..///token/token.sol";   // -> /token/token.sol
import "..////token/token.sol";  // -> /token/token.sol
import "../////token/token.sol"; // -> /token/token.sol
```

#### Slashes in base path follow the same rules as slashes in imports
```solidity
// Base path: ////base1////base2/////base3////
import "token/token.sol"; // -> /base1/base2/base3/token/token.sol
```

#### Slashes in remappings must match exactly
```solidity
// Remappings: /tmp/code=/usr/lib
import "/tmp//code/token.sol";    // -> /tmp/code/token.sol
import "/tmp/code/token.sol/";    // -> /usr/lib/token.sol/
import "/tmp/code/token.sol//";   // -> /usr/lib/token.sol/
import "//tmp/code/token.sol";    // -> //tmp/code/token.sol
import "///tmp/code/token.sol";   // -> /tmp/code/token.sol
```

```solidity
// Remappings: /tmp/code/token.sol//=/usr/lib/token.sol
import "/tmp/code/token.sol";    // -> /usr/lib/token.sol
import "/tmp/code/token.sol/";   // -> /usr/lib/token.sol/.
import "/tmp/code/token.sol//";  // -> /usr/lib/token.sol
import "/tmp/code/token.sol///"; // -> /usr/lib/token.sol/.
```

#### Multiple trailing slashes in remapping targets are squashed into one
```solidity
// Remappings: /tmp/code=////usr////lib////
import "/tmp/code/token.sol"; // -> /usr/lib/token.sol
```

### URLs

#### `file://` prefix is stripped from paths
```solidity
import "file:///tmp/code/token.sol"; // -> /tmp/code/token.sol
import "/tmp/code/file://token.sol"; // -> /tmp/code/file:/token.sol
```

#### Other protocol prefixes are not stripped
```solidity
import "http:///tmp/code/token.sol";  // -> /home/user/work/http:/tmp/code/token.sol
import "https:///tmp/code/token.sol"; // -> /home/user/work/https:/tmp/code/token.sol
import "ftp:///tmp/code/token.sol";   // -> /home/user/work/ftp:/tmp/code/token.sol
```

#### Paths that become relative after stripping of `file://` are always relative to the current working directory
```solidity
import "file://token.sol";    // -> /home/user/work/token.sol
import "file://./token.sol";  // -> /home/user/work/token.sol
import "file://../token.sol"; // -> /home/user/token.sol
```

#### Base path is prepended to paths that become relative after stripping of `file://`
```solidity
// Base path: /base
import "file://token.sol";    // -> /base/home/user/work/token.sol
```

#### Prepending base path to paths that start with `.` or `..` after stripping of `file://` makes them relative to the source directory
```solidity
// Base path: /base
import "file://./token.sol";  // -> /base/project/token.sol
import "file://../token.sol"; // -> /base/token.sol
```

#### `file://` prefix as a whole cannot be remapped
```solidity
// Remappings: file://=/usr/lib
import "file:///tmp/code/token.sol"; // -> /tmp/code/token.sol
```

```solidity
// Remappings: file:/=/usr/lib
import "file:///tmp/code/token.sol"; // -> /tmp/code/token.sol
```

#### Fragments of the `file://` prefix can be remapped
```solidity
// Remappings: file=/usr/lib
import "file:///tmp/code/token.sol"; // -> /usr/lib:/tmp/code/token.sol
```

```solidity
// Remappings: f=/usr/lib
import "file:///tmp/code/token.sol"; // -> /usr/libile:/tmp/code/token.sol
```

Buggy import path resolution in corner cases with remappings and base path #11036

Description

Issues

Current path resolution behavior

Common setup for all examples below

Simple imports

Absolute

Relative imports are relative to current working directory

Relative imports starting with . or .. are relative to the source directory

Relative imports going beyond root directory ignore .. and are relative to the current working directory

Path Remapping

Absolute imports can be remapped

Relative imports can be remapped

Relative imports can be remapped into absolute imports

Absolute imports can be remapped into imports relative to the current working directory

Absolute imports can be remapped into imports starting with . or .. but they are also relative to the current working directory

Only prefix can be remapped

The remapping with the longest matching prefix is used

Remapping is not recursive

The last remapping takes precedence

Remappings do not have to match whole path segments

Leading . and .. in imports cannot be remapped

Parts of the path that . and .. get resolved into can get remapped

Remapping of . and .. works differently when the path to the source file given to the compiler is relative

Example: Current working directory is a prefix of the source directory

Paths are not canonicalized before remapping

Remappings ignore any number of leading . and .. segments in imports going beyond the root directory

Remappings ignore any number of leading . and .. segments when the path to the source file given to the compiler is relative

Example: Current working directory is a prefix of the source directory

Current working directory path cannot be remapped

Source directory path can be remapped

Base Path

Base path does not affect absolute imports

Base path replaces current working directory in relative imports

Base path is prepended to source directory path in imports starting with . or ..

Relative imports going beyond root directory ignore .. and are relative to the base directory

Base path is prepended to remapped absolute imports

Base path replaces current working directory in remapped relative imports

Base path is prepended to relative imports remapped into absolute imports

Base path replaces current working directory in absolute imports remapped to relative imports

Base path replaces source directory in absolute imports remapped to relative imports starting with . or ..

Parts of the path that . and .. get resolved into can get remapped when base path is used and such remappings don't override the base path

Base path cannot be remapped

Source directory path can be remapped even when base path is used

Relative base path is relative to the current working directory

Standard input

Standard input can be used as if it was an actual file called <stdin> if requested

A file called <stdin> from current working directory can only be imported if use of the standard input is not requested.

<stdin> can be remapped to a path when it represents standard input

<stdin> can be remapped to a path when it represents a file

Paths can be remapped to <stdin> when it represents standard input

Paths can be remapped to <stdin> when it represents a file

Base path does not affect <stdin> when it represents standard input

Base path affects <stdin> when it does not represent standard input

Extra Slashes

Multiple slashes between path segments in imports are squashed into one

Trailing slashes in imports are replaced with /.

Trailing slashes in relative imports that start with . or .. imports are stripped

Two Leading slashes in imports are preserved

More than two Leading slashes in imports are squashed into one

Slashes after the leading . or .. in relative imports are squashed into one

Slashes in base path follow the same rules as slashes in imports

Slashes in remappings must match exactly

Multiple trailing slashes in remapping targets are squashed into one

URLs

file:// prefix is stripped from paths

Other protocol prefixes are not stripped

Paths that become relative after stripping of file:// are always relative to the current working directory

Base path is prepended to paths that become relative after stripping of file://

Prepending base path to paths that start with . or .. after stripping of file:// makes them relative to the source directory

file:// prefix as a whole cannot be remapped

Fragments of the file:// prefix can be remapped

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Relative imports starting with `.` or `..` are relative to the source directory

Relative imports going beyond root directory ignore `..` and are relative to the current working directory

Absolute imports can be remapped into imports starting with `.` or `..` but they are also relative to the current working directory

Leading `.` and `..` in imports cannot be remapped

Parts of the path that `.` and `..` get resolved into can get remapped

Remapping of `.` and `..` works differently when the path to the source file given to the compiler is relative

Remappings ignore any number of leading `.` and `..` segments in imports going beyond the root directory

Remappings ignore any number of leading `.` and `..` segments when the path to the source file given to the compiler is relative

Base path is prepended to source directory path in imports starting with `.` or `..`

Relative imports going beyond root directory ignore `..` and are relative to the base directory

Base path replaces source directory in absolute imports remapped to relative imports starting with `.` or `..`

Parts of the path that `.` and `..` get resolved into can get remapped when base path is used and such remappings don't override the base path

Standard input can be used as if it was an actual file called `<stdin>` if requested

A file called `<stdin>` from current working directory can only be imported if use of the standard input is not requested.

`<stdin>` can be remapped to a path when it represents standard input

`<stdin>` can be remapped to a path when it represents a file

Paths can be remapped to `<stdin>` when it represents standard input

Paths can be remapped to `<stdin>` when it represents a file

Base path does not affect `<stdin>` when it represents standard input

Base path affects `<stdin>` when it does not represent standard input

Trailing slashes in imports are replaced with `/.`

Trailing slashes in relative imports that start with `.` or `..` imports are stripped

Slashes after the leading `.` or `..` in relative imports are squashed into one

`file://` prefix is stripped from paths

Paths that become relative after stripping of `file://` are always relative to the current working directory

Base path is prepended to paths that become relative after stripping of `file://`

Prepending base path to paths that start with `.` or `..` after stripping of `file://` makes them relative to the source directory

`file://` prefix as a whole cannot be remapped

Fragments of the `file://` prefix can be remapped