From c60e63e2b763f7e59adc77fd97bfa6c9378b540a Mon Sep 17 00:00:00 2001 From: Rebecca Turner Date: Wed, 6 Dec 2023 12:42:53 -0800 Subject: [PATCH] Print the value in `error: cannot coerce` messages This extends the `error: cannot coerce a TYPE to a string` message to print the value that could not be coerced. This helps with debugging by making it easier to track down where the value is being produced from, especially in errors with deep or unhelpful stack traces. --- .../print-value-in-error-cannot-coerce.md | 38 +++++++++++++++++++ .../src/language/string-interpolation.md | 2 +- src/libexpr/eval.cc | 10 +++-- ...al-fail-bad-string-interpolation-1.err.exp | 2 +- ...al-fail-bad-string-interpolation-3.err.exp | 2 +- tests/unit/libexpr/error_traces.cc | 28 +++++++------- 6 files changed, 61 insertions(+), 21 deletions(-) create mode 100644 doc/manual/rl-next/print-value-in-error-cannot-coerce.md diff --git a/doc/manual/rl-next/print-value-in-error-cannot-coerce.md b/doc/manual/rl-next/print-value-in-error-cannot-coerce.md new file mode 100644 index 000000000000..f8873f0dd03c --- /dev/null +++ b/doc/manual/rl-next/print-value-in-error-cannot-coerce.md @@ -0,0 +1,38 @@ +synopsis: Prints the failing value in `error: cannot coerce` messages +issues: #561 +prs: #9553 +description: { + +The `error: cannot coerce a to a string` message now includes the value +which caused the error. This makes debugging much easier: + +``` +$ nix repl nixpkgs +nix-repl> nixpkgs = legacyPackages.x86_64-linux.path +nix-repl> system = { system = "x86_64-linux"; } +nix-repl> import nixpkgs { inherit system; } +error: + … while evaluating a branch condition + + at /nix/store/7g8wbm1z6948x0qma4hzkkb9a3xys76w-source/pkgs/stdenv/booter.nix:64:9: + + 63| go = pred: n: + 64| if n == len + | ^ + 65| then rnul pred + + … while calling the 'length' builtin + + at /nix/store/7g8wbm1z6948x0qma4hzkkb9a3xys76w-source/pkgs/stdenv/booter.nix:62:13: + + 61| let + 62| len = builtins.length list; + | ^ + 63| go = pred: n: + + (stack trace truncated; use '--show-trace' to show the full trace) + + error: cannot coerce a set to a string: { system = "x86_64-linux"; } +``` + +} diff --git a/doc/manual/src/language/string-interpolation.md b/doc/manual/src/language/string-interpolation.md index e999b287b9c6..6e28d26646bc 100644 --- a/doc/manual/src/language/string-interpolation.md +++ b/doc/manual/src/language/string-interpolation.md @@ -189,7 +189,7 @@ If neither is present, an error is thrown. > "${a}" > ``` > -> error: cannot coerce a set to a string +> error: cannot coerce a set to a string: { } > > at «string»:4:2: > diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index 7e68e6f9b742..b52274b64e1e 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -26,9 +26,9 @@ #include #include #include -#include #include #include +#include #include #include @@ -2286,7 +2286,7 @@ BackedStringView EvalState::coerceToString( return std::move(*maybeString); auto i = v.attrs->find(sOutPath); if (i == v.attrs->end()) { - error("cannot coerce %1% to a string", showType(v)) + error("cannot coerce %1% to a string: %2%", showType(v), printValue(*this, v)) .withTrace(pos, errorCtx) .debugThrow(); } @@ -2332,7 +2332,7 @@ BackedStringView EvalState::coerceToString( } } - error("cannot coerce %1% to a string", showType(v)) + error("cannot coerce %1% to a string: %2%", showType(v), printValue(*this, v)) .withTrace(pos, errorCtx) .debugThrow(); } @@ -2691,8 +2691,10 @@ void EvalState::printStatistics() std::string ExternalValueBase::coerceToString(const Pos & pos, NixStringContext & context, bool copyMore, bool copyToStore) const { + std::strstream printed; + print(printed); throw TypeError({ - .msg = hintfmt("cannot coerce %1% to a string", showType()) + .msg = hintfmt("cannot coerce %1% to a string: %2%", showType(), printed.str()) }); } diff --git a/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp b/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp index eb73e9a52986..e54ecc6d1a73 100644 --- a/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp +++ b/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp @@ -7,4 +7,4 @@ error: | ^ 2| - error: cannot coerce a function to a string + error: cannot coerce a function to a string: diff --git a/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp b/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp index ac14f329b787..6f0a96f78dd3 100644 --- a/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp +++ b/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp @@ -7,4 +7,4 @@ error: | ^ 2| - error: cannot coerce a function to a string + error: cannot coerce a function to a string: diff --git a/tests/unit/libexpr/error_traces.cc b/tests/unit/libexpr/error_traces.cc index 81498f65a3f8..c2403bee938f 100644 --- a/tests/unit/libexpr/error_traces.cc +++ b/tests/unit/libexpr/error_traces.cc @@ -295,7 +295,7 @@ namespace nix { TEST_F(ErrorTraceTest, toPath) { ASSERT_TRACE2("toPath []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the first argument passed to builtins.toPath")); ASSERT_TRACE2("toPath \"foo\"", @@ -309,7 +309,7 @@ namespace nix { TEST_F(ErrorTraceTest, storePath) { ASSERT_TRACE2("storePath true", TypeError, - hintfmt("cannot coerce %s to a string", "a Boolean"), + hintfmt("cannot coerce %s to a string: %s", "a Boolean", "true"), hintfmt("while evaluating the first argument passed to 'builtins.storePath'")); } @@ -318,7 +318,7 @@ namespace nix { TEST_F(ErrorTraceTest, pathExists) { ASSERT_TRACE2("pathExists []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while realising the context of a path")); ASSERT_TRACE2("pathExists \"zorglub\"", @@ -332,7 +332,7 @@ namespace nix { TEST_F(ErrorTraceTest, baseNameOf) { ASSERT_TRACE2("baseNameOf []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the first argument passed to builtins.baseNameOf")); } @@ -377,7 +377,7 @@ namespace nix { TEST_F(ErrorTraceTest, filterSource) { ASSERT_TRACE2("filterSource [] []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the second argument (the path to filter) passed to 'builtins.filterSource'")); ASSERT_TRACE2("filterSource [] \"foo\"", @@ -1038,7 +1038,7 @@ namespace nix { TEST_F(ErrorTraceTest, toString) { ASSERT_TRACE2("toString { a = 1; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ a = 1; }"), hintfmt("while evaluating the first argument passed to builtins.toString")); } @@ -1057,7 +1057,7 @@ namespace nix { ASSERT_TRACE2("substring 0 3 {}", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the third argument (the string) passed to builtins.substring")); ASSERT_TRACE1("substring (-3) 3 \"sometext\"", @@ -1070,7 +1070,7 @@ namespace nix { TEST_F(ErrorTraceTest, stringLength) { ASSERT_TRACE2("stringLength {} # TODO: context is missing ???", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the argument passed to builtins.stringLength")); } @@ -1143,7 +1143,7 @@ namespace nix { ASSERT_TRACE2("concatStringsSep \"foo\" [ 1 2 {} ] # TODO: coerce to string is buggy", TypeError, - hintfmt("cannot coerce %s to a string", "an integer"), + hintfmt("cannot coerce %s to a string: %s", "an integer", "1"), hintfmt("while evaluating one element of the list of strings to concat passed to builtins.concatStringsSep")); } @@ -1229,12 +1229,12 @@ namespace nix { ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'system' of derivation 'foo'")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'outputs' of derivation 'foo'")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"drv\"; }", @@ -1279,17 +1279,17 @@ namespace nix { ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; args = [ {} ]; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating an element of the argument list")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; args = [ \"a\" {} ]; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating an element of the argument list")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; FOO = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'FOO' of derivation 'foo'")); }