Create export file before first benchmark (#340)

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ## Changes
 
+- When `--export-*` commands are used, result files are created before benchmark execution
+  to fail early in case of, e.g., wrong permissions. See #306 (@s1ck). 
 - When `--export-*` options are used, result files are written after each individual 
   benchmark command instead of writing after all benchmarks have finished. See #306 (@s1ck).
 

src/hyperfine/export/mod.rs

@@ -8,7 +8,7 @@ use self::csv::CsvExporter;
 use self::json::JsonExporter;
 use self::markdown::MarkdownExporter;
 
-use std::fs::File;
+use std::fs::{File, OpenOptions};
 use std::io::{Result, Write};
 
 use crate::hyperfine::types::BenchmarkResult;
@@ -55,7 +55,9 @@ impl ExportManager {
     }
 
     /// Add an additional exporter to the ExportManager
-    pub fn add_exporter(&mut self, export_type: ExportType, filename: &str) {
+    pub fn add_exporter(&mut self, export_type: ExportType, filename: &str) -> Result<()> {
+        let _ = File::create(filename)?;
+
         let exporter: Box<dyn Exporter> = match export_type {
             ExportType::Asciidoc => Box::new(AsciidocExporter::default()),
             ExportType::Csv => Box::new(CsvExporter::default()),
@@ -66,6 +68,8 @@ impl ExportManager {
             exporter,
             filename: filename.to_string(),
         });
+
+        Ok(())
     }
 
     /// Write the given results to all Exporters contained within this manager
@@ -80,6 +84,6 @@ impl ExportManager {
 
 /// Write the given content to a file with the specified name
 fn write_to_file(filename: &str, content: &[u8]) -> Result<()> {
-    let mut file = File::create(filename)?;
+    let mut file = OpenOptions::new().write(true).open(filename)?;
     file.write_all(content)
 }

src/main.rs

@@ -71,8 +71,11 @@ fn run(
 fn main() {
     let matches = get_arg_matches(env::args_os());
     let options = build_hyperfine_options(&matches);
-    let export_manager = build_export_manager(&matches);
     let commands = build_commands(&matches);
+    let export_manager = match build_export_manager(&matches) {
+        Ok(export_manager) => export_manager,
+        Err(ref e) => error(&e.to_string())
+    };
 
     let res = match options {
         Ok(ref opts) => run(&commands, &opts, &export_manager),
@@ -202,20 +205,21 @@ fn build_hyperfine_options<'a>(
 
 /// Build the ExportManager that will export the results specified
 /// in the given ArgMatches
-fn build_export_manager(matches: &ArgMatches<'_>) -> ExportManager {
+fn build_export_manager(matches: &ArgMatches<'_>) -> io::Result<ExportManager> {
     let mut export_manager = ExportManager::new();
     {
-        let mut add_exporter = |flag, exporttype| {
+        let mut add_exporter = |flag, exporttype| -> io::Result<()> {
             if let Some(filename) = matches.value_of(flag) {
-                export_manager.add_exporter(exporttype, filename);
+                export_manager.add_exporter(exporttype, filename)?;
             }
+            Ok(())
         };
-        add_exporter("export-asciidoc", ExportType::Asciidoc);
-        add_exporter("export-json", ExportType::Json);
-        add_exporter("export-csv", ExportType::Csv);
-        add_exporter("export-markdown", ExportType::Markdown);
+        add_exporter("export-asciidoc", ExportType::Asciidoc)?;
+        add_exporter("export-json", ExportType::Json)?;
+        add_exporter("export-csv", ExportType::Csv)?;
+        add_exporter("export-markdown", ExportType::Markdown)?;
     }
-    export_manager
+    Ok(export_manager)
 }
 
 /// Build the commands to benchmark