Let clap handle all CLI parsing errors (rust-lang#2656)

This PR removes some ad-hoc error propagation that the CLI parser had for more sophisticated arguments and just uses `clap::Error` for everything.

bindgen-cli/options.rs

@@ -1,13 +1,14 @@
 use bindgen::callbacks::TypeKind;
 use bindgen::{
-    builder, AliasVariation, Builder, CodegenConfig, EnumVariation,
+    builder, Abi, AliasVariation, Builder, CodegenConfig, EnumVariation,
     FieldVisibilityKind, Formatter, MacroTypeVariation, NonCopyUnionStyle,
     RegexSet, RustTarget, DEFAULT_ANON_FIELDS_PREFIX, RUST_TARGET_STRINGS,
 };
+use clap::error::{Error, ErrorKind};
 use clap::{CommandFactory, Parser};
 use std::fs::File;
-use std::io::{self, Error, ErrorKind};
-use std::path::PathBuf;
+use std::io;
+use std::path::{Path, PathBuf};
 use std::process::exit;
 
 fn rust_target_help() -> String {
@@ -18,7 +19,9 @@ fn rust_target_help() -> String {
     )
 }
 
-fn parse_codegen_config(what_to_generate: &str) -> io::Result<CodegenConfig> {
+fn parse_codegen_config(
+    what_to_generate: &str,
+) -> Result<CodegenConfig, Error> {
     let mut config = CodegenConfig::empty();
     for what in what_to_generate.split(',') {
         match what {
@@ -29,9 +32,9 @@ fn parse_codegen_config(what_to_generate: &str) -> io::Result<CodegenConfig> {
             "constructors" => config.insert(CodegenConfig::CONSTRUCTORS),
             "destructors" => config.insert(CodegenConfig::DESTRUCTORS),
             otherwise => {
-                return Err(Error::new(
-                    ErrorKind::Other,
-                    format!("Unknown generate item: {}", otherwise),
+                return Err(Error::raw(
+                    ErrorKind::InvalidValue,
+                    format!("Unknown codegen item kind: {}", otherwise),
                 ));
             }
         }
@@ -40,20 +43,64 @@ fn parse_codegen_config(what_to_generate: &str) -> io::Result<CodegenConfig> {
     Ok(config)
 }
 
+fn parse_rustfmt_config_path(path_str: &str) -> Result<PathBuf, Error> {
+    let path = Path::new(path_str);
+
+    if !path.is_absolute() {
+        return Err(Error::raw(
+            ErrorKind::InvalidValue,
+            "--rustfmt-configuration-file needs to be an absolute path!",
+        ));
+    }
+
+    if path.to_str().is_none() {
+        return Err(Error::raw(
+            ErrorKind::InvalidUtf8,
+            "--rustfmt-configuration-file contains non-valid UTF8 characters.",
+        ));
+    }
+
+    Ok(path.to_path_buf())
+}
+
+fn parse_abi_override(abi_override: &str) -> Result<(Abi, String), Error> {
+    let (regex, abi_str) = abi_override
+        .rsplit_once('=')
+        .ok_or_else(|| Error::raw(ErrorKind::InvalidValue, "Missing `=`"))?;
+
+    let abi = abi_str
+        .parse()
+        .map_err(|err| Error::raw(ErrorKind::InvalidValue, err))?;
+
+    Ok((abi, regex.to_owned()))
+}
+
+fn parse_custom_derive(
+    custom_derive: &str,
+) -> Result<(Vec<String>, String), Error> {
+    let (regex, derives) = custom_derive
+        .rsplit_once('=')
+        .ok_or_else(|| Error::raw(ErrorKind::InvalidValue, "Missing `=`"))?;
+
+    let derives = derives.split(',').map(|s| s.to_owned()).collect();
+
+    Ok((derives, regex.to_owned()))
+}
+
 #[derive(Parser, Debug)]
 #[clap(
     about = "Generates Rust bindings from C/C++ headers.",
-    override_usage = "bindgen [FLAGS] [OPTIONS] [HEADER] -- [CLANG_ARGS]...",
+    override_usage = "bindgen <FLAGS> <OPTIONS> <HEADER> -- <CLANG_ARGS>...",
     trailing_var_arg = true
 )]
 struct BindgenCommand {
     /// C or C++ header file.
-    header: Option<String>,
+    header: String,
     /// Path to write depfile to.
     #[arg(long)]
     depfile: Option<String>,
-    /// The default style of code used to generate enums.
-    #[arg(long, value_name = "VARIANT")]
+    /// The default STYLE of code used to generate enums.
+    #[arg(long, value_name = "STYLE")]
     default_enum_style: Option<EnumVariation>,
     /// Mark any enum whose name matches REGEX as a set of bitfield flags.
     #[arg(long, value_name = "REGEX")]
@@ -73,11 +120,11 @@ struct BindgenCommand {
     /// Mark any enum whose name matches REGEX as a module of constants.
     #[arg(long, value_name = "REGEX")]
     constified_enum_module: Vec<String>,
-    /// The default signed/unsigned type for C macro constants.
-    #[arg(long, value_name = "VARIANT")]
+    /// The default signed/unsigned TYPE for C macro constants.
+    #[arg(long, value_name = "TYPE")]
     default_macro_constant_type: Option<MacroTypeVariation>,
-    /// The default style of code used to generate typedefs.
-    #[arg(long, value_name = "VARIANT")]
+    /// The default STYLE of code used to generate typedefs.
+    #[arg(long, value_name = "STYLE")]
     default_alias_style: Option<AliasVariation>,
     /// Mark any typedef alias whose name matches REGEX to use normal type aliasing.
     #[arg(long, value_name = "REGEX")]
@@ -88,7 +135,7 @@ struct BindgenCommand {
     /// Mark any typedef alias whose name matches REGEX to have a new type with Deref and DerefMut to the inner type.
     #[arg(long, value_name = "REGEX")]
     new_type_alias_deref: Vec<String>,
-    /// The default style of code used to generate unions with non-Copy members. Note that ManuallyDrop was first stabilized in Rust 1.20.0.
+    /// The default STYLE of code used to generate unions with non-Copy members. Note that ManuallyDrop was first stabilized in Rust 1.20.0.
     #[arg(long, value_name = "STYLE")]
     default_non_copy_union_style: Option<NonCopyUnionStyle>,
     /// Mark any union whose name matches REGEX and who has a non-Copy member to use a bindgen-generated wrapper for fields.
@@ -169,10 +216,10 @@ struct BindgenCommand {
     /// Output bindings for builtin definitions, e.g. __builtin_va_list.
     #[arg(long)]
     builtins: bool,
-    /// Use the given prefix before raw types instead of ::std::os::raw.
+    /// Use the given PREFIX before raw types instead of ::std::os::raw.
     #[arg(long, value_name = "PREFIX")]
     ctypes_prefix: Option<String>,
-    /// Use the given prefix for anonymous fields.
+    /// Use the given PREFIX for anonymous fields.
     #[arg(long, default_value = DEFAULT_ANON_FIELDS_PREFIX, value_name = "PREFIX")]
     anon_fields_prefix: String,
     /// Time the different bindgen phases and print to stderr
@@ -184,7 +231,7 @@ struct BindgenCommand {
     /// Output our internal IR for debugging purposes.
     #[arg(long)]
     emit_ir: bool,
-    /// Dump graphviz dot file.
+    /// Dump a graphviz dot file to PATH.
     #[arg(long, value_name = "PATH")]
     emit_ir_graphviz: Option<String>,
     /// Enable support for C++ namespaces.
@@ -232,8 +279,8 @@ struct BindgenCommand {
     /// Add a raw line of Rust code at the beginning of output.
     #[arg(long)]
     raw_line: Vec<String>,
-    /// Add a raw line of Rust code to a given module.
-    #[arg(long, number_of_values = 2, value_names = ["MODULE-NAME", "RAW-LINE"])]
+    /// Add a RAW_LINE of Rust code to a given module with name MODULE_NAME.
+    #[arg(long, number_of_values = 2, value_names = ["MODULE_NAME", "RAW_LINE"])]
     module_raw_line: Vec<String>,
     #[arg(long, help = rust_target_help())]
     rust_target: Option<RustTarget>,
@@ -277,16 +324,16 @@ struct BindgenCommand {
     /// `--formatter=none` instead.
     #[arg(long)]
     no_rustfmt_bindings: bool,
-    /// Which tool should be used to format the bindings
+    /// Which FORMATTER should be used for the bindings
     #[arg(
         long,
         value_name = "FORMATTER",
         conflicts_with = "no_rustfmt_bindings"
     )]
     formatter: Option<Formatter>,
-    /// The absolute path to the rustfmt configuration file. The configuration file will be used for formatting the bindings. This parameter sets `formatter` to `rustfmt`.
-    #[arg(long, value_name = "PATH", conflicts_with = "no_rustfmt_bindings")]
-    rustfmt_configuration_file: Option<String>,
+    /// The absolute PATH to the rustfmt configuration file. The configuration file will be used for formatting the bindings. This parameter sets `formatter` to `rustfmt`.
+    #[arg(long, value_name = "PATH", conflicts_with = "no_rustfmt_bindings", value_parser=parse_rustfmt_config_path)]
+    rustfmt_configuration_file: Option<PathBuf>,
     /// Avoid deriving PartialEq for types matching REGEX.
     #[arg(long, value_name = "REGEX")]
     no_partialeq: Vec<String>,
@@ -311,10 +358,10 @@ struct BindgenCommand {
     /// Use `*const [T; size]` instead of `*const T` for C arrays
     #[arg(long)]
     use_array_pointers_in_arguments: bool,
-    /// The name to be used in a #[link(wasm_import_module = ...)] statement
+    /// The NAME to be used in a #[link(wasm_import_module = ...)] statement
     #[arg(long, value_name = "NAME")]
     wasm_import_module_name: Option<String>,
-    /// Use dynamic loading mode with the given library name.
+    /// Use dynamic loading mode with the given library NAME.
     #[arg(long, value_name = "NAME")]
     dynamic_loading: Option<String>,
     /// Require successful linkage to all functions in the library.
@@ -344,36 +391,36 @@ struct BindgenCommand {
     /// Deduplicates extern blocks.
     #[arg(long)]
     merge_extern_blocks: bool,
-    /// Overrides the ABI of functions matching REGEX. The OVERRIDE value must be of the shape REGEX=ABI where ABI can be one of C, stdcall, efiapi, fastcall, thiscall, aapcs, win64 or C-unwind.
-    #[arg(long, value_name = "OVERRIDE")]
-    override_abi: Vec<String>,
+    /// Overrides the ABI of functions matching REGEX. The OVERRIDE value must be of the shape REGEX=ABI where ABI can be one of C, stdcall, efiapi, fastcall, thiscall, aapcs, win64 or C-unwind<.>
+    #[arg(long, value_name = "OVERRIDE", value_parser = parse_abi_override)]
+    override_abi: Vec<(Abi, String)>,
     /// Wrap unsafe operations in unsafe blocks.
     #[arg(long)]
     wrap_unsafe_ops: bool,
     /// Derive custom traits on any kind of type. The CUSTOM value must be of the shape REGEX=DERIVE where DERIVE is a coma-separated list of derive macros.
-    #[arg(long, value_name = "CUSTOM")]
-    with_derive_custom: Vec<String>,
+    #[arg(long, value_name = "CUSTOM", value_parser = parse_custom_derive)]
+    with_derive_custom: Vec<(Vec<String>, String)>,
     /// Derive custom traits on a `struct`. The CUSTOM value must be of the shape REGEX=DERIVE where DERIVE is a coma-separated list of derive macros.
-    #[arg(long, value_name = "CUSTOM")]
-    with_derive_custom_struct: Vec<String>,
+    #[arg(long, value_name = "CUSTOM", value_parser = parse_custom_derive)]
+    with_derive_custom_struct: Vec<(Vec<String>, String)>,
     /// Derive custom traits on an `enum. The CUSTOM value must be of the shape REGEX=DERIVE where DERIVE is a coma-separated list of derive macros.
-    #[arg(long, value_name = "CUSTOM")]
-    with_derive_custom_enum: Vec<String>,
+    #[arg(long, value_name = "CUSTOM", value_parser = parse_custom_derive)]
+    with_derive_custom_enum: Vec<(Vec<String>, String)>,
     /// Derive custom traits on a `union`. The CUSTOM value must be of the shape REGEX=DERIVE where DERIVE is a coma-separated list of derive macros.
-    #[arg(long, value_name = "CUSTOM")]
-    with_derive_custom_union: Vec<String>,
+    #[arg(long, value_name = "CUSTOM", value_parser = parse_custom_derive)]
+    with_derive_custom_union: Vec<(Vec<String>, String)>,
     /// Generate wrappers for `static` and `static inline` functions.
     #[arg(long, requires = "experimental")]
     wrap_static_fns: bool,
-    /// Sets the path for the source file that must be created due to the presence of `static` and
+    /// Sets the PATH for the source file that must be created due to the presence of `static` and
     /// `static inline` functions.
     #[arg(long, requires = "experimental", value_name = "PATH")]
     wrap_static_fns_path: Option<PathBuf>,
-    /// Sets the suffix added to the extern wrapper functions generated for `static` and `static
+    /// Sets the SUFFIX added to the extern wrapper functions generated for `static` and `static
     /// inline` functions.
     #[arg(long, requires = "experimental", value_name = "SUFFIX")]
     wrap_static_fns_suffix: Option<String>,
-    /// Set the default visibility of fields, including bitfields and accessor methods for
+    /// Set the default VISIBILITY of fields, including bitfields and accessor methods for
     /// bitfields. This flag is ignored if the `--respect-cxx-access-specs` flag is used.
     #[arg(long, value_name = "VISIBILITY")]
     default_visibility: Option<FieldVisibilityKind>,
@@ -542,11 +589,7 @@ where
 
     let mut builder = builder();
 
-    if let Some(header) = header {
-        builder = builder.header(header);
-    } else {
-        return Err(Error::new(ErrorKind::Other, "Header not found"));
-    }
+    builder = builder.header(header);
 
     if let Some(rust_target) = rust_target {
         builder = builder.rust_target(rust_target);
@@ -874,23 +917,7 @@ where
         builder = builder.formatter(formatter);
     }
 
-    if let Some(path_str) = rustfmt_configuration_file {
-        let path = PathBuf::from(path_str);
-
-        if !path.is_absolute() {
-            return Err(Error::new(
-                ErrorKind::Other,
-                "--rustfmt-configuration-file needs to be an absolute path!",
-            ));
-        }
-
-        if path.to_str().is_none() {
-            return Err(Error::new(
-                ErrorKind::Other,
-                "--rustfmt-configuration-file contains non-valid UTF8 characters.",
-            ));
-        }
-
+    if let Some(path) = rustfmt_configuration_file {
         builder = builder.rustfmt_configuration_file(Some(path));
     }
 
@@ -976,13 +1003,7 @@ where
         builder = builder.merge_extern_blocks(true);
     }
 
-    for abi_override in override_abi {
-        let (regex, abi_str) = abi_override
-            .rsplit_once('=')
-            .expect("Invalid ABI override: Missing `=`");
-        let abi = abi_str
-            .parse()
-            .unwrap_or_else(|err| panic!("Invalid ABI override: {}", err));
+    for (abi, regex) in override_abi {
         builder = builder.override_abi(abi, regex);
     }
 
@@ -1052,12 +1073,7 @@ where
         ),
     ] {
         let name = emit_diagnostics.then_some(name);
-        for custom_derive in custom_derives {
-            let (regex, derives) = custom_derive
-                .rsplit_once('=')
-                .expect("Invalid custom derive argument: Missing `=`");
-            let derives = derives.split(',').map(|s| s.to_owned()).collect();
-
+        for (derives, regex) in custom_derives {
             let mut regex_set = RegexSet::new();
             regex_set.insert(regex);
             regex_set.build_with_diagnostics(false, name);