[lex.phases] - C++20 → C++23

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 ## Phases of translation <a id="lex.phases">[[lex.phases]]</a>
 The precedence among the syntax rules of translation is specified by the
 following phases.[^1]
-1.  Physical source file characters are mapped, in an
- *implementation-defined* manner, to the basic source character set
- (introducing new-line characters for end-of-line indicators) if
- necessary. The set of physical source file characters accepted is
-    *implementation-defined*. Any source file character not in the basic
- source character set [[lex.charset]] is replaced by the
-    *universal-character-name* that designates that character. An
- implementation may use any internal encoding, so long as an actual
- extended character encountered in the source file, and the same
- extended character expressed in the source file as a
- *universal-character-name* (e.g., using the `\uXXXX` notation), are
- handled equivalently except where this replacement is reverted
- [[lex.pptoken]] in a raw string literal.
-2.  Each instance of a backslash character (\\ immediately followed by a
- new-line character is deleted, splicing physical source lines to
- form logical source lines. Only the last backslash on any physical
- source line shall be eligible for being part of such a splice.
- Except for splices reverted in a raw string literal, if a splice
- results in a character sequence that matches the syntax of a
     *universal-character-name*, the behavior is undefined. A source file
     that is not empty and that does not end in a new-line character, or
-    that ends in a new-line character immediately preceded by a
- backslash character before any such splicing takes place, shall be
-    processed as if an additional new-line character were appended to
-    the file.
 3.  The source file is decomposed into preprocessing tokens
-    [[lex.pptoken]] and sequences of white-space characters (including
     comments). A source file shall not end in a partial preprocessing
     token or in a partial comment.[^2] Each comment is replaced by one
     space character. New-line characters are retained. Whether each
-    nonempty sequence of white-space characters other than new-line is
-    retained or replaced by one space character is unspecified. The
- process of dividing a source file’s characters into preprocessing
- tokens is context-dependent. \[*Example 1*: See the handling of `<`
- within a `#include` preprocessing directive. — *end example*]
 4.  Preprocessing directives are executed, macro invocations are
-    expanded, and `_Pragma` unary operator expressions are executed. If
- a character sequence that matches the syntax of a
- *universal-character-name* is produced by token concatenation
-    [[cpp.concat]], the behavior is undefined. A `#include`
-    preprocessing directive causes the named header or source file to be
-    processed from phase 1 through phase 4, recursively. All
     preprocessing directives are then deleted.
-5.  Each basic source character set member in a *character-literal* or a
-    *string-literal*, as well as each escape sequence and
- *universal-character-name* in a *character-literal* or a non-raw
- string literal, is converted to the corresponding member of the
-    execution character set ([[lex.ccon]], [[lex.string]]); if there is
-    no corresponding member, it is converted to an
-    *implementation-defined* member other than the null (wide)
-    character.[^3]
-6.  Adjacent string literal tokens are concatenated.
-7.  White-space characters separating tokens are no longer significant.
     Each preprocessing token is converted into a token [[lex.token]].
-    The resulting tokens are syntactically and semantically analyzed and
- translated as a translation unit. \[*Note 1*: The process of
-    analyzing and translating the tokens may occasionally result in one
-    token being replaced by a sequence of other tokens
-    [[temp.names]]. — *end note*] It is *implementation-defined*
-    whether the sources for module units and header units on which the
-    current translation unit has an interface dependency (
-    [[module.unit]], [[module.import]]) are required to be available.
-    \[*Note 2*: Source files, translation units and translated
-    translation units need not necessarily be stored as files, nor need
-    there be any one-to-one correspondence between these entities and
-    any external representation. The description is conceptual only, and
-    does not specify any particular implementation. — *end note*]
 8.  Translated translation units and instantiation units are combined as
-    follows: \[*Note 3*: Some or all of these may be supplied from a
     library. — *end note*] Each translated translation unit is examined
-    to produce a list of required instantiations. \[*Note 4*: This may
     include instantiations which have been explicitly requested
     [[temp.explicit]]. — *end note*] The definitions of the required
     templates are located. It is *implementation-defined* whether the
     source of the translation units containing these definitions is
-    required to be available. \[*Note 5*: An implementation could encode
-    sufficient information into the translated translation unit so as to
-    ensure the source is not required here. — *end note*] All the
-    required instantiations are performed to produce *instantiation
-    units*. \[*Note 6*: These are similar to translated translation
-    units, but contain no references to uninstantiated templates and no
-    template definitions. — *end note*] The program is ill-formed if
-    any instantiation fails.
 9.  All external entity references are resolved. Library components are
     linked to satisfy external references to entities not defined in the
     current translation. All such translator output is collected into a
     program image which contains information needed for execution in its
     execution environment.

 ## Phases of translation <a id="lex.phases">[[lex.phases]]</a>
 The precedence among the syntax rules of translation is specified by the
 following phases.[^1]
+1.  An implementation shall support input files that are a sequence of
+ UTF-8 code units (UTF-8 files). It may also support an
+ *implementation-defined* set of other kinds of input files, and, if
+ so, the kind of an input file is determined in an
+    *implementation-defined* manner that includes a means of designating
+ input files as UTF-8 files, independent of their content.
+ \[*Note 1*: In other words, recognizing the U+feff (byte order mark)
+ is not sufficient. — *end note*] If an input file is determined to
+ be a UTF-8 file, then it shall be a well-formed UTF-8 code unit
+ sequence and it is decoded to produce a sequence of Unicode scalar
+ values. A sequence of translation character set elements is then
+ formed by mapping each Unicode scalar value to the corresponding
+ translation character set element. In the resulting sequence, each
+    pair of characters in the input sequence consisting of
+ U+000d (carriage return) followed by U+000a (line feed), as well as
+ each U+000d (carriage return) not immediately followed by a
+ U+000a (line feed), is replaced by a single new-line character. For
+ any other kind of input file supported by the implementation,
+ characters are mapped, in an *implementation-defined* manner, to a
+    sequence of translation character set elements [[lex.charset]],
+    representing end-of-line indicators as new-line characters.
+2.  If the first translation character is U+feff (byte order mark), it
+    is deleted. Each sequence of a backslash character (\\ immediately
+    followed by zero or more whitespace characters other than new-line
+    followed by a new-line character is deleted, splicing physical
+    source lines to form logical source lines. Only the last backslash
+    on any physical source line shall be eligible for being part of such
+    a splice. Except for splices reverted in a raw string literal, if a
+    splice results in a character sequence that matches the syntax of a
     *universal-character-name*, the behavior is undefined. A source file
     that is not empty and that does not end in a new-line character, or
+    that ends in a splice, shall be processed as if an additional
+ new-line character were appended to the file.
 3.  The source file is decomposed into preprocessing tokens
+    [[lex.pptoken]] and sequences of whitespace characters (including
     comments). A source file shall not end in a partial preprocessing
     token or in a partial comment.[^2] Each comment is replaced by one
     space character. New-line characters are retained. Whether each
+    nonempty sequence of whitespace characters other than new-line is
+    retained or replaced by one space character is unspecified. As
+ characters from the source file are consumed to form the next
+ preprocessing token (i.e., not being consumed as part of a comment
+ or other forms of whitespace), except when matching a
+    *c-char-sequence*, *s-char-sequence*, *r-char-sequence*,
+    *h-char-sequence*, or *q-char-sequence*, *universal-character-name*s
+    are recognized and replaced by the designated element of the
+    translation character set. The process of dividing a source file’s
+    characters into preprocessing tokens is context-dependent.
+    \[*Example 1*: See the handling of `<` within a `#include`
+    preprocessing directive. — *end example*]
 4.  Preprocessing directives are executed, macro invocations are
+    expanded, and `_Pragma` unary operator expressions are executed. A
+ `#include` preprocessing directive causes the named header or source
+ file to be processed from phase 1 through phase 4, recursively. All
     preprocessing directives are then deleted.
+5.  For a sequence of two or more adjacent *string-literal* tokens, a
+ common *encoding-prefix* is determined as specified in
+ [[lex.string]]. Each such *string-literal* token is then considered
+    to have that common *encoding-prefix*.
+6.  Adjacent *string-literal* tokens are concatenated [[lex.string]].
+7.  Whitespace characters separating tokens are no longer significant.
     Each preprocessing token is converted into a token [[lex.token]].
+    The resulting tokens constitute a *translation unit* and are
+ syntactically and semantically analyzed and translated.
+ \[*Note 2*: The process of analyzing and translating the tokens can
+ occasionally result in one token being replaced by a sequence of
+ other tokens [[temp.names]]. — *end note*] It is
+ *implementation-defined* whether the sources for module units and
+ header units on which the current translation unit has an interface
+ dependency [[module.unit]], [[module.import]] are required to be
+ available. \[*Note 3*: Source files, translation units and
+ translated translation units need not necessarily be stored as
+ files, nor need there be any one-to-one correspondence between these
+ entities and any external representation. The description is
+ conceptual only, and does not specify any particular
+    implementation. — *end note*]
 8.  Translated translation units and instantiation units are combined as
+    follows: \[*Note 4*: Some or all of these can be supplied from a
     library. — *end note*] Each translated translation unit is examined
+    to produce a list of required instantiations. \[*Note 5*: This can
     include instantiations which have been explicitly requested
     [[temp.explicit]]. — *end note*] The definitions of the required
     templates are located. It is *implementation-defined* whether the
     source of the translation units containing these definitions is
+    required to be available. \[*Note 6*: An implementation can choose
+ to encode sufficient information into the translated translation
+ unit so as to ensure the source is not required here. — *end note*]
+ All the required instantiations are performed to produce
+ *instantiation units*. \[*Note 7*: These are similar to translated
+ translation units, but contain no references to uninstantiated
+ templates and no template definitions. — *end note*] The program is
+ ill-formed if any instantiation fails.
 9.  All external entity references are resolved. Library components are
     linked to satisfy external references to entities not defined in the
     current translation. All such translator output is collected into a
     program image which contains information needed for execution in its
     execution environment.

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