src/libsyntax_ext/test_harness.rs

// Code that generates a test runner to run all the tests in a crate

use log::debug;
use smallvec::{smallvec, SmallVec};
use rustc_feature::Features;
use rustc_target::spec::PanicStrategy;
use syntax::ast::{self, Ident};
use syntax::attr;
use syntax::entry::{self, EntryPointType};
use syntax_expand::base::{ExtCtxt, Resolver};
use syntax_expand::expand::{AstFragment, ExpansionConfig};
use syntax::mut_visit::{*, ExpectOne};
use syntax::ptr::P;
use syntax::sess::ParseSess;
use syntax::source_map::respan;
use syntax::symbol::{sym, Symbol};
use syntax_pos::{Span, DUMMY_SP};
use syntax_pos::hygiene::{AstPass, SyntaxContext, Transparency};

use std::{iter, mem};

struct Test {
    span: Span,
    ident: Ident,
}

struct TestCtxt<'a> {
    ext_cx: ExtCtxt<'a>,
    panic_strategy: PanicStrategy,
    def_site: Span,
    test_cases: Vec<Test>,
    reexport_test_harness_main: Option<Symbol>,
    test_runner: Option<ast::Path>,
}

// Traverse the crate, collecting all the test functions, eliding any
// existing main functions, and synthesizing a main test harness
pub fn inject(
    sess: &ParseSess,
    resolver: &mut dyn Resolver,
    should_test: bool,
    krate: &mut ast::Crate,
    span_diagnostic: &errors::Handler,
    features: &Features,
    panic_strategy: PanicStrategy,
    platform_panic_strategy: PanicStrategy,
    enable_panic_abort_tests: bool,
) {
    // Check for #![reexport_test_harness_main = "some_name"] which gives the
    // main test function the name `some_name` without hygiene. This needs to be
    // unconditional, so that the attribute is still marked as used in
    // non-test builds.
    let reexport_test_harness_main =
        attr::first_attr_value_str_by_name(&krate.attrs, sym::reexport_test_harness_main);

    // Do this here so that the test_runner crate attribute gets marked as used
    // even in non-test builds
    let test_runner = get_test_runner(span_diagnostic, &krate);

    if should_test {
        let panic_strategy = match (panic_strategy, enable_panic_abort_tests) {
            (PanicStrategy::Abort, true) =>
                PanicStrategy::Abort,
            (PanicStrategy::Abort, false) if panic_strategy == platform_panic_strategy => {
                // Silently allow compiling with panic=abort on these platforms,
                // but with old behavior (abort if a test fails).
                PanicStrategy::Unwind
            }
            (PanicStrategy::Abort, false) => {
                span_diagnostic.err("building tests with panic=abort is not supported \
                                     without `-Zpanic_abort_tests`");
                PanicStrategy::Unwind
            }
            (PanicStrategy::Unwind, _) => PanicStrategy::Unwind,
        };
        generate_test_harness(sess, resolver, reexport_test_harness_main,
                              krate, features, panic_strategy, test_runner)
    }
}

struct TestHarnessGenerator<'a> {
    cx: TestCtxt<'a>,
    tests: Vec<Test>,
}

impl<'a> MutVisitor for TestHarnessGenerator<'a> {
    fn visit_crate(&mut self, c: &mut ast::Crate) {
        noop_visit_crate(c, self);

        // Create a main function to run our tests
        c.module.items.push(mk_main(&mut self.cx));
    }

    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
        let mut item = i.into_inner();
        if is_test_case(&item) {
            debug!("this is a test item");

            let test = Test {
                span: item.span,
                ident: item.ident,
            };
            self.tests.push(test);
        }

        // We don't want to recurse into anything other than mods, since
        // mods or tests inside of functions will break things
        if let ast::ItemKind::Mod(mut module) = item.kind {
            let tests = mem::take(&mut self.tests);
            noop_visit_mod(&mut module, self);
            let mut tests = mem::replace(&mut self.tests, tests);

            if !tests.is_empty() {
                let parent = if item.id == ast::DUMMY_NODE_ID {
                    ast::CRATE_NODE_ID
                } else {
                    item.id
                };
                // Create an identifier that will hygienically resolve the test
                // case name, even in another module.
                let expn_id = self.cx.ext_cx.resolver.expansion_for_ast_pass(
                    module.inner,
                    AstPass::TestHarness,
                    &[],
                    Some(parent),
                );
                for test in &mut tests {
                    // See the comment on `mk_main` for why we're using
                    // `apply_mark` directly.
                    test.ident.span = test.ident.span.apply_mark(expn_id, Transparency::Opaque);
                }
                self.cx.test_cases.extend(tests);
            }
            item.kind = ast::ItemKind::Mod(module);
        }
        smallvec![P(item)]
    }

    fn visit_mac(&mut self, _mac: &mut ast::Mac) {
        // Do nothing.
    }
}

/// A folder used to remove any entry points (like fn main) because the harness
/// generator will provide its own
struct EntryPointCleaner {
    // Current depth in the ast
    depth: usize,
    def_site: Span,
}

impl MutVisitor for EntryPointCleaner {
    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
        self.depth += 1;
        let item = noop_flat_map_item(i, self).expect_one("noop did something");
        self.depth -= 1;

        // Remove any #[main] or #[start] from the AST so it doesn't
        // clash with the one we're going to add, but mark it as
        // #[allow(dead_code)] to avoid printing warnings.
        let item = match entry::entry_point_type(&item, self.depth) {
            EntryPointType::MainNamed |
            EntryPointType::MainAttr |
            EntryPointType::Start =>
                item.map(|ast::Item {id, ident, attrs, kind, vis, span, tokens}| {
                    let allow_ident = Ident::new(sym::allow, self.def_site);
                    let dc_nested = attr::mk_nested_word_item(
                        Ident::from_str_and_span("dead_code", self.def_site),
                    );
                    let allow_dead_code_item = attr::mk_list_item(allow_ident, vec![dc_nested]);
                    let allow_dead_code = attr::mk_attr_outer(allow_dead_code_item);

                    ast::Item {
                        id,
                        ident,
                        attrs: attrs.into_iter()
                            .filter(|attr| {
                                !attr.check_name(sym::main) && !attr.check_name(sym::start)
                            })
                            .chain(iter::once(allow_dead_code))
                            .collect(),
                        kind,
                        vis,
                        span,
                        tokens,
                    }
                }),
            EntryPointType::None |
            EntryPointType::OtherMain => item,
        };

        smallvec![item]
    }

    fn visit_mac(&mut self, _mac: &mut ast::Mac) {
        // Do nothing.
    }
}

/// Crawl over the crate, inserting test reexports and the test main function
fn generate_test_harness(sess: &ParseSess,
                         resolver: &mut dyn Resolver,
                         reexport_test_harness_main: Option<Symbol>,
                         krate: &mut ast::Crate,
                         features: &Features,
                         panic_strategy: PanicStrategy,
                         test_runner: Option<ast::Path>) {
    let mut econfig = ExpansionConfig::default("test".to_string());
    econfig.features = Some(features);

    let ext_cx = ExtCtxt::new(sess, econfig, resolver);

    let expn_id = ext_cx.resolver.expansion_for_ast_pass(
        DUMMY_SP,
        AstPass::TestHarness,
        &[sym::main, sym::test, sym::rustc_attrs],
        None,
    );
    let def_site = DUMMY_SP.with_def_site_ctxt(expn_id);

    // Remove the entry points
    let mut cleaner = EntryPointCleaner { depth: 0, def_site };
    cleaner.visit_crate(krate);

    let cx = TestCtxt {
        ext_cx,
        panic_strategy,
        def_site,
        test_cases: Vec::new(),
        reexport_test_harness_main,
        test_runner
    };

    TestHarnessGenerator {
        cx,
        tests: Vec::new(),
    }.visit_crate(krate);
}

/// Creates a function item for use as the main function of a test build.
/// This function will call the `test_runner` as specified by the crate attribute
///
/// By default this expands to
///
/// #[main]
/// pub fn main() {
///     extern crate test;
///     test::test_main_static(&[
///         &test_const1,
///         &test_const2,
///         &test_const3,
///     ]);
/// }
///
/// Most of the Ident have the usual def-site hygiene for the AST pass. The
/// exception is the `test_const`s. These have a syntax context that has two
/// opaque marks: one from the expansion of `test` or `test_case`, and one
/// generated  in `TestHarnessGenerator::flat_map_item`. When resolving this
/// identifier after failing to find a matching identifier in the root module
/// we remove the outer mark, and try resolving at its def-site, which will
/// then resolve to `test_const`.
///
/// The expansion here can be controlled by two attributes:
///
/// `reexport_test_harness_main` provides a different name for the `main`
/// function and `test_runner` provides a path that replaces
/// `test::test_main_static`.
fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
    let sp = cx.def_site;
    let ecx = &cx.ext_cx;
    let test_id = Ident::new(sym::test, sp);

    let runner_name = match cx.panic_strategy {
        PanicStrategy::Unwind => "test_main_static",
        PanicStrategy::Abort => "test_main_static_abort",
    };

    // test::test_main_static(...)
    let mut test_runner = cx.test_runner.clone().unwrap_or(
        ecx.path(sp, vec![test_id, ecx.ident_of(runner_name, sp)]));

    test_runner.span = sp;

    let test_main_path_expr = ecx.expr_path(test_runner);
    let call_test_main = ecx.expr_call(sp, test_main_path_expr,
                                       vec![mk_tests_slice(cx, sp)]);
    let call_test_main = ecx.stmt_expr(call_test_main);

    // extern crate test
    let test_extern_stmt = ecx.stmt_item(sp, ecx.item(sp,
        test_id,
        vec![],
        ast::ItemKind::ExternCrate(None)
    ));

    // #[main]
    let main_meta = ecx.meta_word(sp, sym::main);
    let main_attr = ecx.attribute(main_meta);

    // pub fn main() { ... }
    let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(vec![]));

    // If no test runner is provided we need to import the test crate
    let main_body = if cx.test_runner.is_none() {
        ecx.block(sp, vec![test_extern_stmt, call_test_main])
    } else {
        ecx.block(sp, vec![call_test_main])
    };

    let decl = ecx.fn_decl(vec![], ast::FunctionRetTy::Ty(main_ret_ty));
    let sig = ast::FnSig { decl, header: ast::FnHeader::default() };
    let main = ast::ItemKind::Fn(sig, ast::Generics::default(), main_body);

    // Honor the reexport_test_harness_main attribute
    let main_id = match cx.reexport_test_harness_main {
        Some(sym) => Ident::new(sym, sp.with_ctxt(SyntaxContext::root())),
        None => Ident::new(sym::main, sp),
    };

    let main = P(ast::Item {
        ident: main_id,
        attrs: vec![main_attr],
        id: ast::DUMMY_NODE_ID,
        kind: main,
        vis: respan(sp, ast::VisibilityKind::Public),
        span: sp,
        tokens: None,
    });

    // Integrate the new item into existing module structures.
    let main = AstFragment::Items(smallvec![main]);
    cx.ext_cx.monotonic_expander().fully_expand_fragment(main).make_items().pop().unwrap()
}

/// Creates a slice containing every test like so:
/// &[&test1, &test2]
fn mk_tests_slice(cx: &TestCtxt<'_>, sp: Span) -> P<ast::Expr> {
    debug!("building test vector from {} tests", cx.test_cases.len());
    let ref ecx = cx.ext_cx;


    ecx.expr_vec_slice(sp,
        cx.test_cases.iter().map(|test| {
            ecx.expr_addr_of(test.span,
                ecx.expr_path(ecx.path(test.span, vec![test.ident])))
        }).collect())
}

fn is_test_case(i: &ast::Item) -> bool {
    attr::contains_name(&i.attrs, sym::rustc_test_marker)
}

fn get_test_runner(sd: &errors::Handler, krate: &ast::Crate) -> Option<ast::Path> {
    let test_attr = attr::find_by_name(&krate.attrs, sym::test_runner)?;
    test_attr.meta_item_list().map(|meta_list| {
        if meta_list.len() != 1 {
            sd.span_fatal(test_attr.span,
                "`#![test_runner(..)]` accepts exactly 1 argument").raise()
        }
        match meta_list[0].meta_item() {
            Some(meta_item) if meta_item.is_word() => meta_item.path.clone(),
            _ => sd.span_fatal(test_attr.span, "`test_runner` argument must be a path").raise()
        }
    })
}