libexpr: diagnostics framework & error recovery basics

src/libexpr/diagnostic.hh

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+/**
+ * diagnostic.hh - This file declares records that related to nix diagnostic
+ *
+ * Diagnostics are structures with a main message,
+ * and optionally some additional information (body).
+ *
+ * For diagnostics with a body,
+ * they may need a special overrided function to format the message.
+ *
+ */
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "error.hh"
+#include "nixexpr.hh"
+
+namespace nix {
+
+/**
+ * The base class for all diagnostics.
+ * concret diagnostic types are defined in Diagnostic*.inc
+ */
+struct Diag
+{
+    /**
+     * The location of some diagnostic, currently it is at the beginning of tokens
+     */
+    PosIdx loc;
+
+    /**
+     * Unique identifier for internal use.
+     */
+    enum Kind {
+#define DIAG_MERGE(SNAME, CNAME, SEVERITY) DK_##CNAME,
+#include "diagnostics/merge.inc"
+    };
+
+    Diag() = default;
+    Diag(PosIdx loc)
+        : loc(loc){};
+
+    /**
+     * Each diagnostic contains a severity field,
+     * should be "Fatal", "Error" or "Warning"
+     * this will affect the eval process.
+     *
+     * "Fatal"   -- non-recoverable while parsing.
+     * "Error"   -- recoverable while parsing, but should not eval
+     * "Warning" -- recoverable while parsing, and we can eval the AST
+     * "Note"    -- some additional information about the error.
+     */
+    enum Severity { DS_Fatal, DS_Error, DS_Warning, DS_Note };
+
+    [[nodiscard]] virtual Kind kind() const = 0;
+
+    /**
+     * \brief short name.
+     * There might be a human readable short name that controls the diagnostic
+     * For example, one may pass -Wno-dup-formal to suppress duplicated formals.
+     * A special case for parsing errors, generated from bison
+     * have the sname "bison"
+     */
+    [[nodiscard]] virtual std::string_view sname() const = 0;
+
+    /** Get severity */
+    [[nodiscard]] virtual Severity severity() const = 0;
+
+    /**
+     * Format printable diagnostic, with string interpolated
+     * e.g. "invalid integer %1%" -> "invalid integer 'bar'"
+     */
+    [[nodiscard]] virtual std::string_view format() const = 0;
+
+    virtual ~Diag() = default;
+
+    static Verbosity getVerb(Severity s)
+    {
+        switch (s) {
+        case DS_Error:
+        case DS_Fatal:
+            return lvlError;
+        case DS_Warning:
+            return lvlWarn;
+        case DS_Note:
+            return lvlNotice;
+        }
+    }
+
+    [[nodiscard]] ErrorInfo getErrorInfo(const PosTable & positions) const
+    {
+        return ErrorInfo{.msg = std::string(format()), .errPos = positions[loc]};
+    }
+
+    using Notes = std::vector<std::shared_ptr<Diag>>;
+
+    [[nodiscard]] virtual Notes getNotes() const
+    {
+        return {};
+    }
+};
+
+struct DiagWithNotes : Diag
+{
+    Diag::Notes notes;
+    [[nodiscard]] Diag::Notes getNotes() const override
+    {
+        return notes;
+    }
+};
+
+#define DIAG_SIMPLE(SNAME, CNAME, SEVERITY, MESSAGE) \
+    struct Diag##CNAME : Diag \
+    { \
+        std::string_view format() const override \
+        { \
+            return MESSAGE; \
+        } \
+        std::string_view sname() const override \
+        { \
+            return SNAME; \
+        } \
+        Severity severity() const override \
+        { \
+            return DS_##SEVERITY; \
+        } \
+        Kind kind() const override \
+        { \
+            return DK_##CNAME; \
+        } \
+        Diag##CNAME() = default; \
+        Diag##CNAME(PosIdx pos) \
+            : Diag(pos) \
+        { \
+        } \
+    };
+#include "diagnostics/kinds.inc"
+#undef DIAG_SIMPLE
+
+#define DIAG_BODY(SNAME, CNAME, SEVERITY, BODY) struct Diag##CNAME : Diag BODY;
+#include "diagnostics/kinds.inc"
+#undef DIAG_BODY
+
+// Implement trivial functions except ::format
+#define DIAG_BODY(SNAME, CNAME, SEVERITY, BODY) \
+    inline std::string_view Diag##CNAME::sname() const \
+    { \
+        return SNAME; \
+    } \
+    inline Diag::Severity Diag##CNAME::severity() const \
+    { \
+        return DS_##SEVERITY; \
+    } \
+    inline Diag::Kind Diag##CNAME::kind() const \
+    { \
+        return DK_##CNAME; \
+    }
+#include "diagnostics/kinds.inc"
+#undef DIAG_BODY
+
+inline DiagInvalidInteger::DiagInvalidInteger(PosIdx loc, std::string text)
+    : Diag(loc)
+    , text(std::move(text))
+{
+    text = hintfmt("invalid integer '%1%'", text).str();
+}
+
+inline DiagInvalidFloat::DiagInvalidFloat(PosIdx loc, std::string text)
+    : Diag(loc)
+    , text(std::move(text))
+{
+    text = hintfmt("invalid float '%1%'", text).str();
+}
+
+inline std::string_view DiagInvalidInteger::format() const
+{
+    return text;
+}
+
+inline std::string_view DiagInvalidFloat::format() const
+{
+    return text;
+}
+
+inline std::string_view DiagBisonParse::format() const
+{
+    return err;
+}
+struct DiagnosticEngine
+{
+    std::vector<std::unique_ptr<Diag>> errors;
+    std::vector<std::unique_ptr<Diag>> warnings;
+
+    void add(std::unique_ptr<Diag> D)
+    {
+        switch (D->severity()) {
+        case Diag::DS_Fatal:
+        case Diag::DS_Error: {
+            errors.emplace_back(std::move(D));
+            break;
+        }
+        case Diag::DS_Warning: {
+            warnings.emplace_back(std::move(D));
+            break;
+        }
+        case Diag::DS_Note: {
+            // todo: unreachble
+            assert(0);
+        }
+        }
+    }
+
+    void checkRaise(const PosTable & positions) const
+    {
+        if (!errors.empty()) {
+            const Diag * back = errors[0].get();
+            throw ParseError(back->getErrorInfo(positions));
+        }
+    }
+};
+
+} // namespace nix

src/libexpr/diagnostics/kinds.inc

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+/// diagnostics/kinds.inc, provides declarations for diagnostics.
+
+// provides: DIAG_SIMPLE(SNAME, CNAME, SEVERITY, MESSAGE)
+// provides: DIAG_BODY(SNAME, CNAME, SEVERITY, BODY)
+// provides: DIAG_NOTE_SIMPLE(SNAME, CNAME, SEVERITY, MESSAGE)
+// provides: DIAG_NOTE_BODY(SNAME, CNAME, SEVERITY, BODY)
+
+//=============================================================================/
+// DIAG_SIMPLE(SName, ClassName, Severity, Message)
+// "simple" means they have no additional body
+//=============================================================================/
+
+#ifdef DIAG_SIMPLE
+DIAG_SIMPLE("path-trailing-slash", PathTrailingSlash, Error, "path has a trailing slash")
+DIAG_SIMPLE("dynamic-in-let", DynamicInLet, Error, "dynamic attributes not allowed in let")
+DIAG_SIMPLE("dynamic-in-inherit", InheritDynamic, Error, "dynamic attributes not allowed in inherit")
+DIAG_SIMPLE("url-literal", URLLiteral, Warning, "url literals are disabled")
+DIAG_SIMPLE("hpath-impure", HPath, Error, "hpath cannot be resolved in pure mode")
+#endif
+
+#define COMMON_BODY \
+    Severity severity() const override; \
+    Kind kind() const override; \
+    std::string_view format() const override; \
+    std::string_view sname() const override;
+
+//=============================================================================/
+// DIAG_BODY(SName, ClassName, Severity, Body)
+// diagnostics with special body
+//=============================================================================/
+#ifdef DIAG_BODY
+DIAG_BODY("bison", BisonParse, Fatal, {
+    std::string err;
+    COMMON_BODY
+})
+DIAG_BODY("invalid-integer", InvalidInteger, Fatal, {
+    std::string text;
+    COMMON_BODY
+    DiagInvalidInteger(PosIdx loc, std::string text);
+})
+
+DIAG_BODY("invalid-float", InvalidFloat, Fatal, {
+    std::string text;
+    COMMON_BODY
+    DiagInvalidFloat(PosIdx loc, std::string text);
+})
+
+#undef COMMON_BODY
+#endif // DIAG_BODY

src/libexpr/diagnostics/merge.inc

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+// diagnostics/merge.inc, merge all declarations
+
+// provides: DIAG_MERGE(SNAME, CNAME, SEVERITY)
+
+#ifdef DIAG_MERGE
+
+#define DIAG_SIMPLE(SNAME, CNAME, SEVERITY, MESSAGE) DIAG_MERGE(SNAME, CNAME, SEVERITY)
+#define DIAG_BODY(SNAME, CNAME, SEVERITY, BODY) DIAG_MERGE(SNAME, CNAME, SEVERITY)
+#define DIAG_NOTE_SIMPLE(SNAME, CNAME, SEVERITY, MESSAGE) DIAG_MERGE(SNAME, CNAME, SEVERITY)
+
+#include "kinds.inc"
+
+#undef DIAG_NOTE_SIMPLE
+#undef DIAG_BODY
+#undef DIAG_SIMPLE
+
+#endif