add integration test to check deprecated configuration warnings

I went through the Configurations.md file and created a test case for
all the deprecated options.

tests/rustfmt/main.rs

@@ -1,5 +1,8 @@
 //! Integration tests for rustfmt.
 
+/// UI tests for rustfmt that verify the stdout / stderr output
+mod ui;
+
 use std::env;
 use std::fs::remove_file;
 use std::path::Path;

tests/rustfmt/ui.rs

@@ -0,0 +1,122 @@
+use super::rustfmt;
+use rustfmt_nightly::test_helpers::{get_test_files, read_significant_comments};
+use std::path::{Path, PathBuf};
+
+/// Transforms the `// rustfmt-{config}: {value}` comments in each test file into a String
+/// that can be passed to rustfmt on the command line like
+/// `--config={config1}={value1},{config2}={value2}
+fn command_line_args_from_significant_comments(path: &Path) -> String {
+    let config_comments = read_significant_comments(path);
+
+    if config_comments.is_empty() {
+        return String::new();
+    }
+
+    let mut config = String::with_capacity(256);
+    config.push_str("--config=");
+
+    let mut iter = config_comments.into_iter().peekable();
+
+    while let Some((key, value)) = iter.next() {
+        let is_last = iter.peek().is_none();
+
+        config.push_str(&key);
+        config.push('=');
+        config.push_str(&value);
+
+        if !is_last {
+            config.push(',')
+        }
+    }
+    config
+}
+
+enum CheckOutputResult {
+    /// The output matches what's in the expected file
+    Okay,
+    /// The expected file doesn't exist and there was no output generated by rustfmt
+    NothingToCheck,
+    /// The output generated by rustfmt doesn't match what's in the expected file
+    MismatchedContent,
+    /// rustfmt generated output but the expected output file does not exist
+    MissingExpectedFile,
+}
+
+/// Compares the input against the output read from a file.
+/// returns `true` if the check was successfull, and `false` otherwise.
+fn check_output_file(output: &str, expected: &Path) -> CheckOutputResult {
+    match (expected.exists(), !output.is_empty()) {
+        (true, _) => {
+            // The file exists so compare it's content with the output.
+            let expected_output =
+                std::fs::read_to_string(expected).expect("to read the file successfully");
+            if expected_output.trim() == output.trim() {
+                CheckOutputResult::Okay
+            } else {
+                CheckOutputResult::MismatchedContent
+            }
+        }
+        (false, true) => {
+            // The file does not exist and the output is not empty.
+            CheckOutputResult::MissingExpectedFile
+        }
+        (false, false) => {
+            // The file doesn't exist, and the output isn't empty
+            CheckOutputResult::NothingToCheck
+        }
+    }
+}
+
+fn ui_test_inenr(files: Vec<PathBuf>, check_stdout: bool, check_stderr: bool) -> usize {
+    if !check_stderr && !check_stdout {
+        panic!("We need to check stdout, stderr, or both");
+    }
+
+    let mut errors = 0;
+
+    let has_errors = |rustfmt_output: &str, output_file: &Path| -> bool {
+        match check_output_file(&rustfmt_output, &output_file) {
+            CheckOutputResult::Okay | CheckOutputResult::NothingToCheck => false,
+            CheckOutputResult::MissingExpectedFile => {
+                eprintln!("Missing {}", output_file.display());
+                eprintln!("Expected content: {}", rustfmt_output);
+                true
+            }
+            CheckOutputResult::MismatchedContent => {
+                eprintln!(
+                    "Expected {} to contain\n{}",
+                    output_file.display(),
+                    rustfmt_output
+                );
+                true
+            }
+        }
+    };
+
+    for file in files {
+        let config = command_line_args_from_significant_comments(&file);
+
+        // deprecation warnings are only emitted on stderr
+        let (stdout, stderr) = rustfmt(&[config.as_str()]);
+
+        if check_stdout {
+            let stdout_file = file.with_extension("stdout");
+            errors += has_errors(&stdout, &stdout_file) as usize;
+        }
+
+        if check_stderr {
+            let stderr_file = file.with_extension("stderr");
+            errors += has_errors(&stderr, &stderr_file) as usize;
+        }
+    }
+
+    errors
+}
+
+/// Check the output for deprecated warnings
+#[test]
+fn deprecated() {
+    let files = get_test_files(&PathBuf::from("tests/ui/deprecated"), true, &[]);
+    let errors = ui_test_inenr(files, false, true);
+    assert!(errors == 0, "All deprecation UI tests should pass")
+}

tests/ui/deprecated/fn_args_layout.rs

@@ -0,0 +1 @@
+// rustfmt-fn_args_layout: Tall

tests/ui/deprecated/fn_args_layout.stderr

@@ -0,0 +1 @@
+Warning: the `fn_args_layout` option is deprecated. Use `fn_params_layout`. instead

tests/ui/deprecated/hide_parse_errors.rs

@@ -0,0 +1 @@
+// rustfmt-hide_parse_errors: true

tests/ui/deprecated/hide_parse_errors.stderr

@@ -0,0 +1 @@
+Warning: the `hide_parse_errors` option is deprecated. Use `show_parse_errors` instead

tests/ui/deprecated/merge_imports.rs

@@ -0,0 +1 @@
+// rustfmt-merge_imports: true

tests/ui/deprecated/merge_imports.stderr

@@ -0,0 +1 @@
+Warning: the `merge_imports` option is deprecated. Use `imports_granularity="Crate"` instead