Initial implementation of swift-format.

Co-authored-by: Alexander Lash <[email protected]>
Co-authored-by: Alfredo Delli Bovi <[email protected]>
Co-authored-by: Andrés Tamez Hdz <[email protected]>
Co-authored-by: Austin Belknap <[email protected]>
Co-authored-by: Harlan Haskins <[email protected]>
Co-authored-by: Lauren White <[email protected]>
Co-authored-by: Tony Allevato <[email protected]>
Co-authored-by: Yuta Saito <[email protected]>

Author: 8 people

.gitignore

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+.build/
+.swiftpm/
+swift-format.xcodeproj/

.gitmodules

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+[submodule "Sources/CCommonMark/cmark"]
+	path = Sources/CCommonMark/cmark
+	url = https://github.com/apple/swift-cmark

Documentation/Configuration.md

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+# `swift-format` Configuration
+
+`swift-format` allows users to configure a subset of its behavior, both when
+used as a command line tool or as an API.
+
+## Command Line Configuration
+
+A `swift-format` configuration file is a JSON file with the following
+top-level keys and values:
+
+*   `version` _(number)_: The version of the configuration file. For now, this
+    should always be `1`.
+
+*   `lineLength` _(number)_: The maximum allowed length of a line, in
+    characters.
+
+*   `indentation` _(object)_: The kind and amount of whitespace that should be
+    added when indenting one level. The object value of this property should
+    have **exactly one of the following properties:**
+
+    *   `spaces` _(number)_: One level of indentation is the given number of
+        spaces.
+    *   `tabs` _(number)_: One level of indentation is the given number of
+        tabs.
+
+*   `tabWidth` _(number)_: The number of spaces that should be considered
+    equivalent to one tab character. This is used during line length
+    calculations when tabs are used for indentation.
+
+*   `maximumBlankLines` _(number)_: The maximum number of consecutive blank
+    lines that are allowed to be present in a source file. Any number larger
+    than this will be collapsed down to the maximum.
+
+*   `respectsExistingLineBreaks` _(boolean)_: Indicates whether or not existing
+    line breaks in the source code should be honored (if they are valid
+    according to the style guidelines being enforced). If this settings is
+    `false`, then the formatter will be more "opinionated" by only inserting
+    line breaks where absolutely necessary and removing any others, effectively
+    canonicalizing the output.
+
+*   `blankLineBetweenMembers` _(object)_: Controls logic specific to the
+    enforcement of blank lines between type members. The object value of this
+    property has the following properties:
+
+    *   `ignoreSingleLineProperties` _(boolean)_: If `true`, then single-line
+        property declarations are allowed to appear consecutively without a
+        blank line separating them.
+
+*   `lineBreakBeforeControlFlowKeywords` _(boolean)_: Determines the
+    line-breaking behavior for control flow keywords that follow a closing
+    brace, like `else` and `catch`. If true, a line break will be added before
+    the keyword, forcing it onto its own line. If false (the default), the
+    keyword will be placed after the closing brace (separated by a space).
+
+*   `lineBreakBeforeEachArgument` _(boolean)_: Determines the line-breaking
+    behavior for generic arguments and function arguments when a declaration is
+    wrapped onto multiple lines. If true (the default), a line break will be
+    added before each argument, forcing the entire argument list to be laid out
+    vertically. If false, arguments will be laid out horizontally first, with
+    line breaks only being fired when the line length would be exceeded.
+
+> TODO: Add support for enabling/disabling specific syntax transformations in
+> the pipeline.
+
+### Example
+
+An example `.swift-format` configuration file is shown below.
+
+```javascript
+{
+    "version": 1,
+    "lineLength": 100,
+    "indentation": {
+        "spaces": 2
+    },
+    "maximumBlankLines": 1,
+    "respectsExistingLineBreaks": true,
+    "blankLineBetweenMembers": {
+        "ignoreSingleLineProperties": true
+    },
+    "lineBreakBeforeControlFlowKeywords": true,
+    "lineBreakBeforeEachArgument": true
+}
+```
+
+## API Configuration
+
+The `SwiftConfiguration` module contains a `Configuration` type that is
+equivalent to the JSON structure described above. (In fact, `Configuration`
+conforms to `Codable` and is how the JSON form is read from and written to
+disk.)
+
+The `SwiftFormatter` and `SwiftLinter` APIs in the `SwiftFormat` module take a
+mandatory `Configuration` argument that specifies how the formatter should
+behave when acting upon source code or syntax trees.
+
+The default initializer for `Configuration` creates a value equivalent to the
+default configuration that would be printed by invoking
+`swift-format --mode dump-configuration`. API users can also provide their own
+configuration by modifying this value or loading it from another source using
+Swift's `Codable` APIs.

Documentation/Development.md

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+# Developing `swift-format`
+
+## Check Out the Submodules
+
+The `CCommonMark` target is a Git submodule that pulls the C code in
+[apple/swift-cmark](https://github.com/apple/swift-cmark) into this
+project.
+
+After you clone this repository, remember to run the following commands
+to make sure those sources are available to the compiler:
+
+```shell
+git submodule init
+git submodule update
+```
+
+## Command Line Options for Debugging
+
+`swift-format` provides some hidden command line options to facilitate
+debugging the tool during development:
+
+* `--debug-disable-pretty-print`: Disables the pretty-printing pass of the
+  formatter, causing only the syntax tree transformations in the first phase
+  pipeline to run.
+
+* `--debug-dump-token-stream`: Dumps a human-readable indented structure
+  representing the pseudotoken stream constructed by the pretty printing
+  phase.
+
+## Support Scripts
+
+The [Scripts](../Scripts) directory contains a `format-diff.sh` script
+that some developers may find useful. When invoked, it rebuilds
+`swift-format` (if necessary to pick up any recent changes) and lets
+you view a side-by-side `diff` with the original file on the left side
+and the formatted output on the right side.
+
+This script will use `colordiff` if it is installed on your `PATH`;
+otherwise, it will fall back to `diff`.