Auto merge of rust-lang#11505 - Alexendoo:metadata-collector-truncate, r=Manishearth

Truncate files when opening in metadata-collector

Fixes the issue seen here rust-lang/rust-clippy#11483 (comment) and in a couple other PRs

The changelog file was opened without truncating it, so if the new version is shorter than the old one stray contents would remain at the end of the file

The other two files first removed the file so didn't have this problem, but in all cases we now use `fs::write`/`File::create` which is write + create + truncate

changelog: none

Author: bors

clippy_lints/src/utils/internal_lints/metadata_collector.rs

@@ -31,7 +31,7 @@ use serde::{Serialize, Serializer};
 use std::collections::{BTreeSet, BinaryHeap};
 use std::fmt;
 use std::fmt::Write as _;
-use std::fs::{self, OpenOptions};
+use std::fs::{self, File};
 use std::io::prelude::*;
 use std::path::{Path, PathBuf};
 use std::process::Command;
@@ -229,25 +229,10 @@ impl Drop for MetadataCollector {
         collect_renames(&mut lints);
 
         // Outputting json
-        if Path::new(JSON_OUTPUT_FILE).exists() {
-            fs::remove_file(JSON_OUTPUT_FILE).unwrap();
-        }
-        let mut file = OpenOptions::new()
-            .write(true)
-            .create(true)
-            .open(JSON_OUTPUT_FILE)
-            .unwrap();
-        writeln!(file, "{}", serde_json::to_string_pretty(&lints).unwrap()).unwrap();
+        fs::write(JSON_OUTPUT_FILE, serde_json::to_string_pretty(&lints).unwrap()).unwrap();
 
         // Outputting markdown
-        if Path::new(MARKDOWN_OUTPUT_FILE).exists() {
-            fs::remove_file(MARKDOWN_OUTPUT_FILE).unwrap();
-        }
-        let mut file = OpenOptions::new()
-            .write(true)
-            .create(true)
-            .open(MARKDOWN_OUTPUT_FILE)
-            .unwrap();
+        let mut file = File::create(MARKDOWN_OUTPUT_FILE).unwrap();
         writeln!(
             file,
             "<!--
@@ -261,17 +246,15 @@ Please use that command to update the file and do not edit it by hand.
         .unwrap();
 
         // Write configuration links to CHANGELOG.md
-        let mut changelog = std::fs::read_to_string(CHANGELOG_PATH).unwrap();
-        let mut changelog_file = OpenOptions::new().read(true).write(true).open(CHANGELOG_PATH).unwrap();
-
-        if let Some(position) = changelog.find("<!-- begin autogenerated links to configuration documentation -->") {
-            // I know this is kinda wasteful, we just don't have regex on `clippy_lints` so... this is the best
-            // we can do AFAIK.
-            changelog = changelog[..position].to_string();
-        }
+        let changelog = std::fs::read_to_string(CHANGELOG_PATH).unwrap();
+        let mut changelog_file = File::create(CHANGELOG_PATH).unwrap();
+        let position = changelog
+            .find("<!-- begin autogenerated links to configuration documentation -->")
+            .unwrap();
         writeln!(
             changelog_file,
-            "{changelog}<!-- begin autogenerated links to configuration documentation -->\n{}\n<!-- end autogenerated links to configuration documentation -->",
+            "{}<!-- begin autogenerated links to configuration documentation -->\n{}\n<!-- end autogenerated links to configuration documentation -->",
+            &changelog[..position],
             self.configs_to_markdown(ClippyConfiguration::to_markdown_link)
         )
         .unwrap();